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Eingeladener Vortrag
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Implementation and current situation of introducing the Directives 97/23/EC in the German legislaton
(2001)
HYDROGEN ONBOARD STORAGE - AN INSERTION OF THE PROBABILISTIC APPROACH INTO STANDARDS & REGULATIONS?
(2005)
Hydrogen onboard storage - an insertion of the probalistic approach into standards & regulations?
(2005)
Hydraulic pressure testing of composite gas cylinders damages the cylinders, but provides very limited information. For this reason, the Federal Institute of Materials Research and Testing (BAM) demands the assessment of the safety of design types for retest periods of more than three years by employing destructive testing of small samples.
This gives insight in properties not quantified by current standards.
Depending on the cycle fatigue behaviour of the individual design type either cycle tests or slow burst tests are employed. In this paper methods are introduced for a statistical assessment of sample results of both test methods. This includes gathering the average and load cycle burst strength, and the scatter of a sample as well as analysing and plotting them as a pair of values. Each pair of values representing a sample can be assessed approximately regarding its survival rate in service, if the introduced performance charts are employed.
The slow burst testing of composite cylinders - Part II: Statistic evaluation of sample test results
(2013)
The strength of unidirectional elastic fibre composites is shown to depend on the loading rate as the viscoelastic nature of the matrix results in a fall in breaking load as the rate is reduced. The simulation of the accumulation of fibre breaks leading to failure, takes into account all physical phenomena involved fibre failure, including the stochastic nature of fibre strength, stress transfer through the matrix between reinforcements, interfacial debonding and the viscoelastic nature of the matrix. The kinetics of composite failure are seen to involve the initial formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The rate at which this occurs depends on the viscoelastic properties of the matrix. These results have been shown to closely mirror the behaviour of carbon fibre composite pressure vessels.
The current practise of focusing the periodic retesting of composite cylinders primarily on the hydraulic pressure test has to be evaluated as critical - with regard to the damage of the specimen as well as in Terms of their significance. This is justified by micro damages caused to the specimen by the test itself and by a lack of informative values. Thus BAM Federal Institute of Materials Research and Testing (Germany) uses a new approach of validation of composite for the determination of re-test periods. It enables the description of the state of a population of composite cylinders based on destructive tests parallel to operation.
An essential aspect of this approach is the prediction of residual safe service life. In cases where it cannot be estimated by means of hydraulic load cycle tests, as a replacement the creep or burst test remains. As a combination of these two test procedures BAM suggests the 'slow burst test SBT'. On this a variety of about 150 burst test results on three design types of cylinders with plastic liners are presented. For this purpose both, the parameters of the test protocol as well as the nature and intensity of the pre-damage artificially aged test samples are analysed statistically. This leads first to an evaluation of the different types of artificial ageing but also to the clear recommendation that conventional burst tests be substituted
totally if indented for assessment of composite pressure receptacles.
The current practice of periodic retesting of composite pressure receptacles primarily based on the hydraulic pressure test has to be evaluated as critical.
This is justified by micro damages caused to the specimen by the test
itself and by a lack of informative values. Thus, BAM Federal Institute of Materials Research and Testing uses a new validation approach in the case of retest periods of more than 5 years. It enables the description of the condition of a specific design type series based on destructive tests parallel to operation. With respect to this approach it is explained how the statistical evaluation of sample tests and their extrapolation to end of life or at least to the time of next retesting can be achieved. In addition, it is explained how the reliability limits may be linked to the size and pressure level of the respective composite pressure receptacle. The frame of this safety Approach includes the influence of the maximum working pressure on the safety assessment.
One topic of this approach is the introduction of the working diagram
essential for safety assessments that allows graphical evaluation of load cycle strength by mean value, scatter and survival rate of samples as well as instruction how to use it. For this, it is explained how the number of filling cycles and the reduction of the respective hydraulic residual cycle strength interacts with the newly introduced value of specific filling sensitivity.
Faserverbundwerkstoffe (Komposite) zeigen außergewöhnliche Veränderungen ihrer Eigenschaften in Abhängigkeit von der Betriebsdauer. Daraus leitet sich auch die Notwendigkeit ab, eine Methode zu finden, die in der Lage ist, Festigkeiten und Restfestigkeiten von Komposit-Druckbehältern zu ermitteln. Dies kann mittels Lastwechselprüfung oder in anderen Fällen vorzugsweise mittels der langsamen Berstprüfung erfolgen. Für eine aussagekräftige Beschreibung der Festigkeit bedürfen die Ergebnisse beider Prüfverfahren einer statistischen Auswertung. Aber insbesondere die statistische Auswertung der berstbezogenen Festigkeitseigenschaften unterliegt neben der Frage der Stichprobengröße einer großen Unsicherheit mit enormen Folgen. Dies ist die Frage, welche Verteilungsfunktion der Streuung der Festigkeitseigenschaft konservativ zugrundegelegt werden darf. So ist zu untersuchen, ob die Gaußsche Normalverteilung (NV) die wahre Verteilung richtig beschreibt. Es könnten aber auch andere Funktionen, wie z. B. die Weibull-Verteilung notwendig sein, um eine Überschätzung der Überlebenswahrscheinlichkeit bzw. Zuverlässigkeit in dem interessanten Bereich von einem Ausfall pro 104 bis 108 Druckbehältern zu vermeiden.
Slow burst testing of samples as a method for quantification of composite cylinder degradation
(2014)
The current practise to focus periodic retesting of composite cylinders primarily on the hydraulic pressure test has to be evaluated as critical. The test itself always causes a certain amount of micro damage to the cylinders but does not necessarily deliver sufficient and evaluable information. Thus BAM Federal Institute of Materials Research and Testing (Germany) moves the focal point to a new approach for validation of composite cylinders, based on destructive sample tests parallel to operation. Statistical assessment of results of these destructive tests is employed for the estimation of remaining safe service life, based on reliability demands. The estimated service life is also used for the determination of re-test periods of the examined population of composite cylinders.
An essential aspect of this approach is the validation of current residual strength and its prediction at any point of service life. In cases of gas cylinders with very high cycle strength, residual strength cannot be quantified statistically by means of hydraulic load cycles. As a replacement, creep tests or burst tests may be employed. BAM suggests the 'slow burst test SBT' as a combination of these two test procedures. This is a compromise between the practicability of the (conventional) burst test and the practical relevance of sustained loads during service, to be tested in creep rupture tests. In this paper, a variety of 99 burst results of a cylinder design type used for breathing apparatus (CFRP with PE-liner) is evaluated. The influence of test procedure parameters and nature and intensity of artificial ageing on the test sample strength are analysed statistically. This leads to an evaluation of different procedures of artificial ageing and the recommendation to substitute conventional burst tests by slow burst tests for the assessment of composite pressure receptacles.
There is evidence that composite materials degrade under static loads. Consequently there is no way to design composite gas cylinders for unlimited service life. Yet this fact is not reflected by design standards for composite receptacles approved for the transport of dangerous goods or for stationary application. Unnecessary cost and weight result from this.
Due to the degradation aspects of composites it is necessary to provide appropriate retesting procedures, which allow rejection of used vessels as is common practice for metallic receptacles. The current procedure of hydraulic tests appears to be an expensive procedure with serious doubts regarding its usefulness for composite cylinders.
Consequently, an efficient method is needed, which allows limiting the life time to its safe maximum. It is thus recommended to combine retesting with the assessment of residual life time. Since relevant non-destructive methods are not yet sufficiently matured and standardized enough, a concept featuring destructive tests on composite cylinders parallel to operation should be considered. An alternative concept introduced here, proposes to substitute the hydraulic testing of 100% of a population by a probabilistic evaluation of destructive tests on samples parallel to operation. Intensified pre-fill inspections should be an additional component of such a concept.
Developers interested in high pressure storage of hydrogen for mobile use increasingly rely on composite cylinders for onboard storage or transport of dangerous goods. Thus, composite materials and systems deserve special consideration. History gives interesting background information important to the understanding of the current situation as to regulations, codes and standards.
Based on this review, origins of different regulations for the storage of hydrogen as dangerous good and as propellant for vehicles will be examined. Both categories started out using steel and sometimes aluminium as cylinder material. With composite materials becoming more common, a new problem emerged: vital input for regulations on composite pressure systems was initially derived from decades of experience with steel cylinders. As a result, both regulatory fields suffer somewhat from this common basis. Only recent developments regarding requirements for composite cylinders have begun to go more and more separate ways. Thus these differences lead to some shortcomings in regulation with respect to composite storage systems.
In principle, in spite of separate development, these deficits are in both applications very much the same: there are uncertainties in the prediction of safe service life, in retesting procedures of composite cylinders and in their intervals. Hence, different aspects of uncertainties and relevant approaches to solutions will be explained.
The explosion of hydrogen gas storage cylinders on May 25, 1894, represents one of the most spectacular failure cases during the late industrialization period in Germany. With respect to modern applications to hydrogen storage as energy carrier, it has several times been referred to as precedent failure case for the whole industrial sector. The detailed investigation reports by Martens have thus gained interest in the last years, but also, because the publications in 1896 about his expertise already provided in September 1894 document one of the first and most comprehensive investigations which can be regarded as a nucleus for modern failure analysis.
After summarizing the newspaper reports in the introduction, the present contribution provides a review of Martens' reports targeted at the development of failure analyses and materials testing procedures as well as potential failure origins.
Emergency response units increasingly use pressure cylinders made from fibre composites for breathing air as elements of personal protective equipment (PPE). Such applications expose the composite cylinders to harsh temperature and handling conditions. At least in Europe, standards have been used for certifying PPE, which are designed and mandatory for the approval of pressure receptacles for the transport of dangerous goods. Therefore, service conditions specific to PPEs are not accounted for in these standards. In this paper, BAM (Federal Institute for Materials Research and Testing) investigates the residual safety of a composite cylinder design at the end of their designated service life of 15 years. The cylinders (test pressure PH 450 bars; 6.8 Litres) are of one design type with aluminium liner and fully wrapped with carbon fibres, which is commonly considered a “Type III” cylinder. All cylinders were used as PPE by the Berlin fire department and randomly picked in three samples of 25 cylinders each before tested.
At BAM, the cylinder samples underwent hydraulic load cycle tests (LCT), conventional burst tests (BT) and so called slow burst tests (SBT). A concept for quantification of strength degradation already introduced by BAM was applied. This concept is based on a probabilistic assessment of the average strength and scatter of each sample of cylinders. The strength distributions of the used PPEcylinders is shown and analysed. Some unexpected effects are shown and a refinement of the statistical assessment is introduced.
Composite materials show a degradation of properties depending on service life. This creates the necessity to find tailored methods to determine strength and residual strength of composite cylinders. The determination can be done e.g. by load cycles tests. The result needs a statistical assessment for the precise description of strength. Especially the statistical assessment of load cycle strength properties has a high uncertainty. It is unclear if a Log-Normal distribution, a WEIBULL distribution or others, describe the scatter behaviour of residual strength properties correctly.
Distribution functions aim at approximating the frequency of occurrence of residual load cycle strength for high survival rates. An assumption has to be found and confirmed to prevent over-estimation of reliability.
Gas cylinders made from composite materials receive growing popularity in applications where light weight is of advantage. At the same time manufacturers are interested in cutting cost and weight through material reduction for better acceptance of a product, e.g. H2-vehicles. This requires a better understanding of safety relevant properties.
The safety determination of current standards is mainly based on the minimum burst pressure of a few specimens. Various research projects were conducted aiming at reducing minimum burst pressure requirements without compromising safety. No satisfying results were found. While looking at reliability aspects it could be concluded, that the minimum burst pressure of unused specimens is not a satisfying criterion for safety during service life.
This paper introduces first ideas for a method to determine one aspect of reliability of composite gas cylinders, employing probabilistic analysis of burst pressures of a sample of specimens. This can create potential for saving material cost while granting a higher safety level than the current method. Additionally, degradation over service time can be assessed.
Composite materials show a degradation of properties depending on Service life. This creates the necessity to find tailored methods to determine strength and residual strength of composite cylinders. The determination can be done e.g. by load cycles tests. The result needs a Statistical assessment for the precise description of strength. Especially the Statistical assessment of load cycle strength properties has a high uncertainty. It is unclear if a Log-Normal distribution, a WEIBULL distribution or others, describe the scatter behaviour of residual strength properties correctly. Distribution functions aim at approximating the frequency of occurrence of residual load cycle strength for high survival rates. An assumption has to be found and confirmed to prevent overestimation of reliability.
Applications by fire brigades expose the composite cylinders to harsh temperature and handling conditions. Standards have been used for certifying composite cylinders, which are designed for transport of dangerous goods and do not reflect service conditions specific to fire brigades. In this paper, the residual safety of a design type (fully wrapped with aluminum and carbon fiber composite) at the end of their service life of 15 yrs is analyzed. One sample underwent hydraulic load cycle (LC) tests, another conventional burst tests, and the third slow burst tests (SBTs). The statistical evaluation and the handling of an unexpected high amount of early failures are shown.
This slides explain the functionality and the procedure of the UN-service life checks as they are operated by BAM as German authority. These are based on the probabilistic approach including evaluation of current safety level and its comparison with assessments of different status of degrdation including extrapolation towards end of safe service life.
The similarity to the approach for determiantion of retest periods by BAM is explained.
Gas cylinders made of composite materials receive growing popularity in light-weight applications. Current standards are mostly based on safety determination relying on minimum amounts of endured load cycles and a minimum burst pressure of a small number of specimens. This paper investigates the possibilities of a probabilistic strength assessment for safety improvements as well as cost and weight savings. The probabilistic assessment is based on destructive testing of small sized samples. The influence of sample size on uncertainty of the assessment is analysed. Furthermore, methods for the assessment of in-service ageing (degradation) are discussed and displayed in performance charts.
The set of slides summarises the expectations of participants discussed during the opening session. Then the most important aspects of the presentations during the first two days are compiled. At the end the conclusions coming out of a joint discussion are presented. This show what participants expect BAM to do for implementation of the PA in near future.
Current standards governing the design, qualification and in-service inspection of carbon fibre composite cylinders do not facilitate to optimise cylinder design. The requirements have been adapted from standards for metallic cylinders and cannot easily quantify the degradation processes in composite materials. In this article, the results of hydraulic and hydrogen pressure cycle life tests performed on composite reinforced tanks with a metal liner (type 3) and with a high density polymer liner (type 4) are shown. Moreover, the degradation measured by means of residual strength of the tanks after the cycling tests have been compared. It has been found that the most critical aging for metal based composite cylinder is the gaseous cycling while type 4 designs seem to be more sensitive to hydraulic cycling at high temperature.
The presentation shows the basics on the graphic comparison of deterministic regulations and probabilistic safety requirements. In doing so, unsafe but approvable areas in the BAM-SPC (sample performance chart) becomes obvious; as the area of not approveable but safe strength properties does.
Finally the semi-porbabilistic approach of GTR#13 (global technical regulation for hydrogen vehicles) is analysed. Relevant figures show again potential of saving material and unsafe areas in case of high scatter at end of life.
There are several aspects that - dependent from the design of a pressure receptacle - cannot be checked by the currently mandatory inspection methods. Therefore, in some cases destructive tests are needed as alternatives. This requires the operation of statistical evaluation methods.
How it works and why it is necessary is shown for the examples of so called over-moulded cylinders and concerning composite cylinders.
This presentation provides the main issue of a probabilistic based safety assessment.
It shows the differences in terms of survival rate between some current deterministic standards and the probabilistic approach.
It deals with three test procedures: slow burst test, cycle test and fire engulfment test.
This presentation shows the most important steps for developing the probabilistic approach PA with a lot of detailed information on test results. It discusses the necessitiy of performing a slow burst test, to which amount degradation can be accepted and how these interacts with aspects of costs etc.
This presentation explains how an PA-based approval concept could work and would substitute the most of deterministic requirements based on a risk based quantification of accepted failure rates.
The concept of a probabilistic approval approach is based on 5 separate types of requirements:
1. Testing and evaluation of properties at Beginning of Life (BoL)
2. Artificial aging with residual strength assessment
3. Testing against dedicated accidental loads
4. Surveillance of production quality
5. Surveillance of degradation/ check of estimated end of life (EoL)
Each of these aspects is visualised by photos and diagrams.
This presentation provides an impression of the boundary condition of the work on composite cylinders on a competent authority. It shows the various kinds of usage, the different tasks and duties around this kind of storage units and the wide spread of technical competence necessary for the substantial research when addressing the legislation. Based on this it shows how we react on changes in the regulations by research and how this influences the regulations, again. As an example, our probabilistic approach is mentioned and drafted for getting mentioned several times during the ongoing set of presentations.
Referring to the inter-departmental project group "Pressure Equipment" and the section "Pressure Equipment-pressure receptacles; Fuel Gas Storage Systems" developed from, it is shown here how research on safety aspects, technical regulations and the activities of the Federal Institute BAM in its role as competent authority interact to the advantage of safety of composite pressure vessels.
Conventional approval requirements exclusively ask for minimum strength values, which have to be met. The probabilistic approach estimates how likely none of the comparatively manufactured units fails during operation.
Both questions are juxtaposed and compared here with respect to the load cycle tests. The influence of the sample sizes is discussed additionally.
Hydrogen is an attractive energy carrier that requires high effort for safe storage. For ensuring safety they have to undergo a challenging approval process. Relevant standards and regulations for composite cylinders used for the transport of for on-board storage of hydrogen are currently based on deterministic (e.g. ISO 11119-3) or semi-probabilistic (UN GTR No. 13) criteria. This paper analysis the properties of such methods in regards to the evaluation of load cycle strength. Their characteristics are compared with the probabilistic approach of the BAM. Based on Monte-Carlo simulations, the available design range (mean value and scatter of strength criteria) of current concepts were exemplarily estimated. The aspect of small sample sizes is analysed and discussed with respect to the evaluation procedures.
Featuring a detailed analysis of current approval requirements and the relevant safety assessment methods for gas cylinders in general and with main focus on composite cylinders for storing ompressed natural gas and hydrogen, this book demonstrates how current regulations and standards limit the ability to reduce cost and weight. Based on this data, it then highlights the potential offered by the proposed approval procedure based on probabilistic safety assessment.
After addressing the economic potential of probabilistic safety assessments, the book details working procedures and improving cycles and (slow) bursts as methods for assessing residual strength. It then discusses methods for statistically evaluating test data, as well as sample- size and distribution character considerations. A definition of sample strength is elaborated in terms of the performance sheets developed by the author. On this basis, it discusses safety as a property of service life and interpreted as an issue of degradation, and explores aspects of artificial aging for simulating the end-of-life reliability level. Lastly, the book considers control and inspection aspects: quality of production, degradation prediction using destructive sample tests parallel to operation, retesting periods and correcting for underand overestimates of safe lifetime.
Presented in schematic diagrams, illustrations and tables, this information enables manufacturers and operators to use this new approach in practice and supports the improvement of current regulations and standards.
Existing standards for the approval of composite cylinders for the transport of compressed hydrogen are currently based on deterministic (ISO 11119-3) and semi-probabilistic (UN GTR No. 13) criteria. This paper analysis the capabilities of these procedures with respect to the evaluation of burst strength. Their characteristics are compared with the probabilistic approach developed at BAM. Based on Monte-Carlo simulations the available design range (mean value and scatter of burst strength) of all concepts are assessed. In addition, the probability of acceptance for potentially unsafe design types is determined.
The results show large areas of burst properties with a sufficient reliability which cannot be used for the design of composite cylinders, due to current approval criteria. On the other hand, existing standards allow the approval of potentially unsafe designs in case of a very high scatter regarding their burst strength.
It is also shown that existing design types are already designed to the limits of the available design area. A further weight and cost reduction of composite cylinders is therefore closely related to the approval criteria. An example based on UN GTR No. 13 shows how an approval criterion can be optimized by using statistical methods. The example shows that a reduced minimum burst pressure can be combined with a lower probability of acceptance for potentially unsafe design types.
Existing regulations and standards for the approval of composite cylinders in hydrogen service are currently based on deterministic criteria (ISO 11119-3, UN GTR No. 13). This paper provides a systematic analysis of the load cycle properties resulting from these regulations and standards. Their characteristics are compared with the probabilistic approach of the BAM. Based on Monte-Carlo simulations the available design range of all concepts is compared. In addition, the probability of acceptance for potentially unsafe design types is determined.
Existing regulations and standards for the approval of composite cylinders in hydrogen service are currently based on deterministic criteria (ISO 11119-3, UN GTR No. 13). This paper provides a systematic analysis of the load cycle properties resulting from these regulations and standards. Their characteristics are compared with the probabilistic approach of the BAM. Based on Monte-Carlo simulations the available design range of all concepts is compared. In addition, the probability of acceptance for potentially unsafe design types is determined.
The increasing amount of composite transport systems for hydrogen leads to new and therefore unknown potential hazards for general public. Due to lack of experience, risks of new technologies tend to be rated higher than existing familiar applications. An approach for probabilistic safety assessment of technologies or products requires the definition of minimal acceptable reliability levels. This ensures that the probability of a critical failure with a certain consequence is limited to an acceptable risk. But what is the acceptable risk and which risk results from specific probabilities of occurrence and consequences? This is always a very complex question. The following example is based on a probabilistic approach for safety assessment of composite cylinders developed at the BAM (Federal Institute for Materials Research and Testing).
The application range of CPV (composite pressure vessels)
is multifaceted. But also the failure forms and the spectrum of measurement methods is manifold. On various, at BAM observed effects, it is shown why the micromechanical analysis of the composites is of such great interest for the prediction of aging effects of CPVs.
Due to high specific stiffness a nd strength properties, fibre reinforced plastics are used more and more often for the construction of pressure vessels. Within a recent research project run by the Federal Institute for Materials Research and Testing (BAM), aging process of composite pressure vessels is investigated in order to be able to give more accurate lifetime predictions in the future. Focus is set on type III pressure vessels consisting of an aluminium tank which is fully wrapped with carbon fibre reinforced plastics. In order to increase high-cycle fatigue, residual stresses are induced into the pressure vessel during manufacturing process. In particular, residual compressive stresses within the inner aluminium layer have been defined as a main parameter affecting fatigue strength. The aim is to identify and evaluate residual stresses of the pressure vessel by analysing its modal parameters. Through the set-up of a finite-element model potential capability and validity for the use of modal analysis is proven and evaluated, considering influences resulting from manufacturing deviations, too. In the following, a number of stress sensitive modes are defined. Based on these preliminary numerical investigations, a test bench is set up in order to measure pressure vessels via an experimental modal analysis. A final critical evaluation regarding the accuracy of the modal analysis is made by comparing experimental results with data obtained through simulations.
This presentation provides general data about BAM, the structure of department 3 and a short impression of the application of pressure vessels for hydrogen in stationary use, supply chain and onboard storage.
It guides to the actions of BAM as competent authority on this area and shows a lot different methods for testing operated at BAM. Based on this additional research has been detected as necessary for a competent tackling of the tasks as competent authority. After having mentioned several important research projects a figure is presented that compares the development of regulations with relevant re-actions of BAM. The outcome was a concept of a risk based definition of accepted failure rates in combination with probability-oriented safety assessment over entire service life.
The second aspect raised at INERIS is the issue of advising the BMVI concerning pressure vessels for hydrogen. Since the pressure is high for saving material consumption and weight there is still high interest in changing regulatory requirements. Therefor we developed an approach for the display of minimum requirements of regulations in diagrams (sample performance charts; SPC) and the probabilistic analysis for these deterministic requirements. This is done by Monte-Carlo simulation and the analysis of acceptance rate and survival rate of basic populations all over the SPC.
This finally provide same knowledge of non-approvable but safe ranges of parameters and even approvable but non-safe constellations. In addition, this analysis allows to optimise deterministic requirements in regulations to the intended level of safety for approved populations of pressure vessels, which is shown on the example of the GTR#13.
This presentation explains how the evaluation of technical requirements in regulations effects safety level. This shown by using the Monte-Carlo experiment consequently.
The first step is to explain how deterministic requirements and how probabilistic requirements work. Then the statistical behaviour of the generally unknown basic population can be described and that his behaviour is independent from the regulatory approach. Subsequently, the concept of evaluating sample test results with respect to deterministic requirements is explained. The item “acceptance rate” of the basic population that is behind each sample and behind each individuum in a sample is defined. On this collective understanding, the differences in evaluation between the probabilistic approach PA and the most important RC&S are discussed. Some areas are validated in contradictorily. Then the parameters for acceptance of burst strength in the UN-GTR#13 are varied and opens the door for an accurate improvement of acceptance criteria. Finally, the special aspects of degradation in load cycle testing are shown. There, two aspects must be differentiated, the current reliability and its degradation by ongoing load cycles. This is a convincing argument against the very common opinion, which means that the number of hydraulically tested load cycles pro-vides a figure for the number of acceptable filling cycles.
This presentation mentions the most important safety items that should be improved from the perspective of Germany.
These are the improvement of the understanding and definition of term "safety", the agreement on procedures for the measurement of safety and the issue of degradation in combination with the safety level to be ensured until end of life.
For using probabilistic experience for the whole production adequate measures for surveillance of the production should additionally become mandatory to be taken into account.
The essential aspects of these issues are shortly explained and highlighted by especially aspects of the slow burst testing with respect to non-cycle fatigue sensitive designs and the hint on the general scatter of properties (Monte-Carlo simulation).
This presentation explains how BAM operates the PA approach for the life-time surveillance based on the measurement of degradation.
The starting point is the sample performance chart (SPC) as developed by BAM. There it is possible to show minimum requirements, sample properties and lines of constant survival rates, these lines are called isoasfalia. The BAM provides a tool for the safety evaluation of results from sample testing. Then the interaction to the micro-mechanical approach of the FiBreMoD-project is linked with the idea of a degradation of strength and reliability. This leads to the methods of burst and cycle testing. For both methods examples are shown and degradation is explained by showing data of two design types. This visualise the determination of safe service life. Finally, statistical aspects of misinterpretation of test results and the reasons for the decision in favour of the slow burst tests are explained.
Small, mobile propane gas vessels are widely spread and comprise additional hazards in case of a surrounding, intensive fire. The aim of the presented work is to holistically investigate the potential consequences of failure of these off-the-shelf propane gas vessels in case of an absence or malfunction of safety devices. In order to generate a statistically valid dataset, a total of 15 identical propane gas bottles without pressure relief device, each containing m = 11 kg of liquid propane, were underfired in horizontal position. For each selected fire type (wood fire, petrol pool fire, propane gas fire), five vessels were tested under identical conditions. Next to extensive camera equipment including a high-speed camera, systems to record the internal pressure of the gas cylinder, the resulting shock wave overpressure (three positions) and the flame and vessel temperature (three + three positions) during the underfiring were used. Also the unsteady, highly dynamical thermal radiation caused by the explosion of the expanding gas cloud was logged. The fragments were georeferenced and weighed after each test. The experiments prove the failure of all the gas cylinders at a burst pressure of pb = [71 … 98 bar] with a fragmentation into up to seven parts (average: four objects) and a subsequent explosion of the expanding vapour after mixing with the surrounding air. The overpressure measured in the close-up range (distance to the cylinder d = 5 m) resulting from the shockwave caused by the cylinder burst was up to pmax = 0.27 bar, which can potentially lead to significant injuries to humans and damage to building structures and infrastructure, especially in connection with the explosion and the resultant thermal radiation. The distance covered by the fragments after the failure was up to r = 260 m; 47% of the fragments hit the ground more than r = 50 m away from the position of failure.
15 identical off-the-shelf propane cylinders (m = 11 kg liquid propane) were underfired. The infrared Radiation of the Explosion, that occurred in the aftermath of the vessel failure, was recorded using four bolometers. These measurements are compared with an estimation of the Maximum intensity gained by an Analysis of the Video data, an Extended Version of the Stefan-Boltzmann law and a BLEVE model.
The developed model has certain limitations of the element size to be used in the simulation to characterise the strength of composite materials. A reduced volume method is proposed in order to reduce the number of degree of freedom of the finite element simulation.This study has revealed certain configuration to be followed to speed up the computation time.
Fibre-reinforced plastics (FRP) especially carbon-fibre-reinforced polymer (CFRP) and glass-fibre-reinforced polymer (GFRP) are commonly used materials in high pressure vessels and storage units for automotive and aerospace purposes. Optical fibres are suitable to be integrated or directly applied to the surface of FRP components. Using optical fibres it is possible to monitor the distributed strain profiles and changes within the fatigue life of a pressure vessel to ensure the operational safety. Within artificial ageing experiments we used swept wavelength interferometry (SWI) based distributed strain sensing for the monitoring of commercial high-pressure composite cylinder. This artificial ageing was performed using test conditions of 503bar pressure load (service pressure 300 bar) and 89 °C for 100 h. The polyimide coated optical fibres were glued to the surface externally in circumferential and axial direction. Using distributed strain sensing (DSS) material expansion of over 0.5% were monitored with sub-centimetre spatial resolution. Within the circumferential direction we observed up to 10 % local fluctuation compared to the median strain caused by inhomogeneous material expansion, which could cause local material fatigue. In addition, we determined material degradation manifested itself as localized remaining material expansion and/or contraction. Results have been validated by other non-destructive methods like digital strip projection.
Defining a Reduced Volume Zone for the Simulation of Burst Test on a Composite Pressure Vessels
(2018)
The random nature of fibre break in composite materials has to be modelled in all part of the structure as it may contain millions of fibres. The reduced volume method was introduced to determine a smaller zone where we could characterise the strength based on the accumulation of fibre break, hence increasing the computation time
Within a current research project at the Federal Institute for Materials Testing and Research (BAM), the degradation process of composite pressure vessels is studied to be able to give more accurate lifetime predictions in future. The presented research is based on type III pressure vessels consisting of an aluminium tank which is fully wrapped with carbon fibre reinforced plastics. Focus is set on the analysis of residual stresses which are induced into the pressure vessel during manufacturing process in order to increase high cycle fatigue. However, with increasing lifetime residual stress conditions do change. To be able to measure and monitor stress conditions, the application of a non-destructive measurement method is aspired.
In this paper, potential of an experimental modal analysis is worked out to capture and monitor aging and degradation effects in pressure vessels. With the presented method, information about changes in residual stress can be obtained via an analysis of the modal parameters. To realize an application, first, a finite element simulation is used to prove and evaluate potential capability and validity. In the following, a test bench is set up and successively optimized in its accuracy and efficiency. Sensitivity of the applied measurement technique is experimentally ascertained trough the measurement of several prestress modified pressure vessels. Finally, experimental results are interpreted and evaluated with the help of numerically gained findings.
The presentation explains the intended way of BAM in tackling the safety issues in the project TAHYA.
The way how the term “safety” is used in TAHYA leads to the need for a more risk-based understanding of safety. Based on this, the Monte Carlo simulation is used to show where the weak points of current regulations are. Thus, a concept for optimization of relevant regulations, codes and standards will be elaborated during the project. For this purpose, it is helpful to improve the currently operated tool for Monte Carlo simulation, which will need additional data for monitoring the outcome. Strength data, that will be determined by BAM and the other partners during the already agreed test program can be used for this purpose without additional effort.
The presentation explains the term “safety” in a broader sense and leads to the need for a more risk-based understanding of safety. Based on this, the Monte Carlo simulation is used to show where the weak points of the ECE R 134 are and in which direction the GTR 13 could be optimized during the currently running phase 2. For this purpose, it is helpful to improve the currently operated tool for Monte Carlo simulation, for which BAM introduced the research idea “MoCaSiB”.
The presentation is divided in two parts, each evaluates a different aspect of safety.
It starts with the analysis of consequences resulting from worst case ruptures of gas cylinders. The number of harmed persons and fatalities dependent from the pressure-volume product and the kind of stored gas. In parallel, there is a national accepted rule for accepted failure rates depending from this pV-product created by BAM. When combining both aspects it become clear that the pressure-volume product can be used as a good indicator for consequences. At a level of about 120 MPa m3 the maximum consequence starts to become catastrophic character. This shows the reason why the representatives of DIN insisted in limiting relevant pV-limits for tubes and cylinders to 1 Mio. bar litres.
The second part gives a raff overview on the parameters influencing the acceptance rates of borderline basic populations. This is added by some slides giving an idea for the improvement of the minimum burst requirement and finally completed by a proposal for improved acceptance criteria for the burst test.
The basic idea is: an increased pV-product of tubes has the be reflected by an increased safety level.
Hydrogen is an attractive energy carrier that requires high effort for safe storage. For ensuring safety, they must undergo a challenging approval process. Relevant standards and regulations for composite cylinders used for the transport of hydrogen and for its onboard storage are currently based on deterministic (e.g. ISO 11119-3) or semi-probabilistic (UN GTR No. 13) criteria. This paper analysis the properties of such methods with respect to the evaluation of load cycle strength. Their characteristics are compared with the probabilistic approach of the BAM. Based on Monte-Carlo simulations, the available design range (mean value and scatter of strength criteria) of current concepts was exemplarily estimated. The aspect of small sample sizes is analysed and discussed with respect to the evaluation procedures.
Storage
(2018)
The whole conference focused on gaps in research concerning hydrogen and hydrogen safety. This presentation focus on storage aspects and shows the current gaps in research from the point of view of the authors. They have differences in background, from university via manufacturer and safety institute to hydrogen operating industry. The different purposes of storage are covered (onboard storage, stationary storage and transport of gases) as well as the different designs (steel to pure composite/plastic).
Hydrogen is an attractive energy carrier that requires high effort for safe storage. For ensuring safety, storage cylinders must undergo a challenging approval process. Relevant standards and regulations for composite cylinders used for the transport of hydrogen and for its onboard storage are currently based on deterministic (e.g. ISO 11119-3) or to some respect semi-probabilistic criteria (UN GTR No. 13; with respect to burst strength).
This paper provides a systematic analysis of the load cycle properties resulting from these regulations and standards. Their characteristics are compared with the probabilistic approach of the Federal Institute for Materials Research and Testing BAM. The most important aspect of comparing different concepts is the rate for accepting designs with potentially unsafe or critical safety properties. This acceptance rate is analysed by operating Monte-Carlo simulations over the available range of production properties.
The reduced volume method has found a particular zone to be used for evaluating the strength of unidirectional composite materials. To validate the method, modelling an experimental test where it has the same basic assumption of the model had been carried out. The result was favourable as the model can predict the average value from the experiment and also the time dependent effect.
Determination of Distribution Function used in MCS on Safety Analysis of Hydrogen Pressure Vessel
(2019)
The test data of static burst strength and load cycle strength of composite pressure vessels are often described by GAUSSian normal or WEIBULL distribution function to perform safety analyses. The goodness of assumed distribution function plays a significant role in the inferential statistics to predict the population properties by using limited test data. Often, GAUSSian and WEIBULL probability nets are empirical methods used to validate the distribution function; Anderson-Darling and Kolmogorov-Smirnov tests are the mostly favorable approaches for Goodness of Fit. However, the different approaches used to determine the parameters of distribution function lead mostly to different conclusions for safety assessments. In this study, six different methods are investigated to show the variations on the rates for accepting the composite pressure vessels according to GTR No. 13 life test procedure. The six methods are: a) Norm-Log based method, b) Least squares regression, c) Weighted least squares regression, d) A linear approach based on good linear unbiased estimators, e) Maximum likelihood estimation and f) The method of moments estimation. In addition, various approaches of ranking function are considered. In the study, Monte Carlo simulations are conducted to generate basic populations based on the distribution functions which are determined using different methods. Then the samples are extracted randomly from a population and evaluated to obtain acceptance rate. Here, the “populations” and “samples” are corresponding to the burst strength or load cycle strength of the pressure vessels made from composite material and a plastic liner (type 4) for the storage of hydrogen. To the end, the results are discussed, and the best reliable methods are proposed.
Safety aspects of the storage containments of hydrogen are independent from the kind of usage: The main criteria is the resistance against the pressure load. On the 2nd level there are aspects specific to the usage as e.g. crash loads etc.
Safety is achieved when the probability (frequency) of a failure during the service life is acceptable!
But an aspect common for all usages is the scatter of properties resulting from the material and the production. Therefore, it is worth to have a look on the current approach of minimum burst ratios from an unknown point of view: the basic populations of a product – based on exemplarily assessments.
According to this approach, several diagrams with Monte-Carlo generated basic populations in new and aged conditions have been shown. Thus, it has been demonstrated that not the conditions at the begin of life are the critical ones. No, the end of life properties are the critical ones.
This has been combined with the acceptance rate of borderline basic populations. The approach of minimum burst ratios leads to the acceptance rate of 40 % and higher for the approval of critical basic populations – critical due to their production scatter.
This problem becomes much more critical when taking into account the unknown effects of degradation and in-service ageing.
Therefore, we cannot support the proposed reduction of minimum burst ratio without having a stronger assessment of production scatter.
It is pertinent to have a correct description of fibre strength described by the twp parameter Weibull distribution when evaluating a type Iv pressure vessel using the fibre break multiscale model developed at Mines ParisTech. Earlier studies have shown a positive comparison result when T600S fibre strength were used. This study has discovered what would be the effect on the predicted strength when T700S strength is used.
Safety criteria for the transport of hydrogen in permanently mounted composite pressure vessels
(2019)
The recent growing of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by tube-trailers in composite pressure vessels. As transport regulation the ADR is applicable in Europe and adjoined regions and used for national transport in EU. This regulation provides requirements based on the burst pressure of each individual pressure vessel, regardless the capabilities of the transported hydrogen and relevant consequences resulting from worst case scenarios. In 2012, BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national requirements concerning the “UN service life checks” etc.) to consider the transported volume and pressure of gases. However, this results in a stringent requirement in case of using large pressure vessels (tubes) on tube-trailers. In the studies presented here, the key safety factors for using hydrogen trailers are identified and reviewed through some safety measures from some countries like Japan, USA and China. Subsequently, the risk, chance, failure consequences of using trailers are evaluated, in addition, the difficulties for approving huge pressure vessels (large tubes) are addressed. There, a maximum acceptable pressure-volume product is defined. Finally, a performance-based criterion for the balance of chance and risk of hydrogen trailers is suggested to add into regulations and consequently into standards for hydrogen trailers.
The presentation summarizes all the safety concerns that have led DIN to reject an ISO project about extremely large gas/hydrogen transport units.
The core point is the consequence potential, which has increased considerably with the scope of the standardization project in comparison with state of the art systems. At the same time, there is a lack of an approach to take into account the reliability requirements that depend on the consequences, at least up to the level of a catastrophe.
Safety criteria for the transport of hydrogen in permanently mounted composite pressure vessels
(2019)
The recent growing of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by batterie vehicles or tube-trailers, both in composite pressure vessels. As transport regulation the ADR is applicable in Europe and adjoined regions and used for national transport in EU. This regulation provides requirements based on the burst pressure of each individual pressure vessel, regardless the capabilities of the transported hydrogen and relevant consequences resulting from worst case scenarios. In 2012, BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national requirements concerning the “UN service life checks” etc. to consider the transported volume and pressure of gases. However, this results in a stringent requirement in case of using large pressure vessels (so called “tubes”) on vehicles. In the studies presented here, the safety measures for hydrogen road transport are identified and reviewed through some safety measures from some countries like Japan, USA and China. Subsequently, the failure consequences of using trailers, the related risks and chances are evaluated. Finally, a chance-related risk criterion is suggested to add into regulations and consequently to be defined as safety goal in standards for hydrogen transport vehicles and consequently for mounted pressure vessels.
The simulation of strength experiments by the Monte-Carlo method enables the numerical generation of data representing a complete populations of composite pressure vessels. In the case of composite pressure vessels used for hydrogen storage, properties like burst strength or fatigue cycle strength are of interest. This paper provides comprehensive information on how populations are generated and how samples can be taken and evaluated; it also explains how to determine the acceptance rate of random samples from simulated populations for passing the approval test "minimum burst pressure". A word of caution is also expressed regarding the evaluation of acceptance rates from a small sample.
The Reduced Volume Method (RVM) has been used to evaluate the multiscale fibre break model developed at Mines ParisTech. It allows the model to be assigned only at certain part of the structures without necessarily compromising the final prediction. An attempt to model a simple unidirectional composite structure has also been carried out and gave a satisfying result. This paper deals with the application of the RVM to real scale type IV composite cylinders, where its stacking sequence was evaluated through micro-CT scans conducted with the collaboration of the University of Southampton. Two modelling geometries were evaluated and compared with the corresponding experimental results.
The presentation reflects the questions that have been raised by member states and NGOs.
As background information details on the question how to choose a suitable salvage pressure receptacle (SPR) are provided. This leads to the need for deleting the volume limitation for SPRs and to the discussions in 2014 and 2016 on this issue.
As an adequate substitution for deleting the volume limit for SPRs it is proposed to limit the pressure receptacles to be stored in by a maximum pressure-volume-value of 1.5 Mio bar-litres.
After some explanations to standardisation projects currently also tackling this pV-limit, some risk-based safety criteria for a limitation are mentioned with the focus of the consequence level and the general avoidance of catastrophic worst case scenarios.
First the acceptance rates resulting from the analysis of different minimum burst ratios and standards are displayed and explained. Especially the problems resulting from a further reduction if the minimum burst ratio are shown.
For a better understanding of these results the process of analysing the acceptance rate is explained in detail. This contains the alleged contradiction between safety of samples due to its scatter while the rejected sample provides a higher mean strength.
Then the importance of batch testing is explained and leads to the recommendation to have a strong interaction between provided mean strength and requested maximum of production scatter.
Safety criteria for the transport of hydrogen in permanently mounted composite pressure vessels
(2020)
The recent growth of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by battery vehicles or tube-trailers, both in composite pressure vessels. As a transport regulation, the ADR is applicable in Europe and adjoined regions, and is used for national transport in the EU. This regulation provides requirements based on the behaviour of each individual pressure vessel, regardless of the pressure of the transported hydrogen and relevant consequences resulting from generally possible worst case scenarios such as sudden rupture. In 2012, the BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national transport requirements concerning the “UN service life checks” etc. to consider the transported volume and pressure of gases. This results in a requirement that becomes more restrictive as the product of pressure and volume increases. In the studies presented here, the safety measures for hydrogen road transport are identified and reviewed through a number of safety measures from countries including Japan, the USA and China. Subsequently, the failure consequences of using trailer vehicles, the related risk and the chance are evaluated. A benefit-related risk criterion is suggested to add to regulations and to be defined as a safety goal in standards for hydrogen transport vehicles and for mounted pressure vessels. Finally, an idea is given for generating probabilistic safety data and for highly efficient evaluation without a significant increase of effort.
We present the results of distributed fiber optic strain sensing for condition monitoring of a hybrid type IV composite fully wrapped pressure vessel using multilayer integrated optical fibers. Distributed strain sensing was performed for a total number of 252,000 load cycles until burst of the vessel. During this ageing test material fatigue could be monitored and spatially localized. Critical material changes were detected 17,000 cycles before material failure. Results have been validated by acoustic emission analysis.
Hydrogen is an attractive energy carrier that requires high effort for safe storage. Forensuring safety, they must undergo a challenging approval process. Relevant standardsand regulations for composite cylinders used for the transport of hydrogen and for its on-board storage are currently based on deterministic (e.g. ISO 11119-3) or semi-probabilistic(UN GTR No. 13) criteria. This paper analysis the properties of such methods withrespect to the evaluation of load cycle strength. Their characteristics are compared withthe probabilistic approach of the BAM. Based on Monte-Carlo simulations, the availabledesign range (mean value and scatter of strength criteria) of current concepts was exem-plarily estimated. The aspect of small sample sizes is analysed and discussed with respectto the evaluation procedures.
The presentation starts with some key figures about BAM. Then it introduces BAM's competence centre H2Safety@BAM and shows aspects of special competence of the centre. It closes with information about the engagement of BAM in European research projects on hydrogen and a reference to our bilingual paper about our hydrogen strategy.
The objective of this work is to find a method that describes the degree of damage from an impact experiment. This experiment was performed on Composite Pressure Vessels (CPV) in order to find the correlation of impact damage to the residual burst pressure. Computed Tomography (CT) approach was used to capture the before and after impact condition of the CPVs. The Wasserstein function was used to calculate how much the after impact image has differed from the original one. In the end, a good correlation was obtained to the residual burst pressure.
The test data for static burst strength and load cycle fatigue strength of pressure vessels can often be well described by Gaussian normal or Weibull distribution functions. There are various approaches which can be used to determine the parameters of the Weibull distribution function; however, the performance of these methods is uncertain. In this study, six methods are evaluated by using the criterion of OSL (observed significance level) from Anderson-Darling (AD) goodness of Fit (GoF), These are: a) the norm-log based method, b) least squares regression, c) weighted least squares regression, d) a linear approach based on good linear unbiased estimators, e) maximum likelihood estimation and f) method of moments estimation. In addition, various approaches of ranking function are considered. The results show that there are no outperforming methods which can be identified clearly, primarily due to the limitation of the small sample size of the test data used for Weibull analysis. This randomness resulting from the sampling is further investigated by using Monte Carlo simulations, concluding that the sample size of the experimental data is more crucial than the exact method used to derive Weibull parameters. Finally, a recommendation is made to consider the uncertainties of the limitations due to the small size for pressure vessel testing and also for general material testing.
Based on the preliminary presentations in this task force it is repeated how a basic population scatters and its degradation influences properties statistically. There is a remainder on the issue of accepting borderline populations due to the minimum burst ratio requirement.
Then it is explained in detail how the analysis of minimum requirements by a Monte-Carlo-simulation works. The result with respect to the further reduced minimum burst ratio of 2.0 is summarised and means a two-step approach of two scatter levels requiring two different minimum burst ratios.
The methods for evaluating batch tests are analysed. A proposal for integration a statistical analysis is described in detail.
Finally, the positive effect of proof testing is shown and its dependence from the real ageing is shown.
This ends in the recommendation to have a stronger and quantitative look on real ageing and to follow the 2 proposed sets of criteria for a safe usage of hydrogen storage systems.
The introduction reflects the political background in Germany and worldwide concerning hydrogen as energy carrier. This leads to available hydrogen strategies and the reaction of BAM by launching the competence centre H2Safety@BAM. Fokus is set on the competence area TestCert, the special role of the division “Safety of Gas Storage Systems” there and its increasing success in research activities.
The main part explains the needs for a risk-controlled market ramp-up concerning hydrogen products and appropriate measures being under development in division 3.5: risk control, tools for consequence estimation and limitation, probabilistic assessment of end of safe life, the efficiency assessment and optimization of current regulations, the structural health monitoring (SHM) with necessary improvement of measures for quality management in the digital world of safety assessment. Last but not least, the wide range of full-scale testing and simulation of worst-case scenarios is explained.
Monte-Carlo-Analysis of Minimum Burst Requirements for Composite Cylinders for Hydrogen Service
(2021)
For achieving Net Zero-aims hydrogen is an indispensable component, probably the main component. For the usage of hydrogen, a wide acceptance is necessary, which requires trust in hydrogen based on absence of major incidents resulting from a high safety level. Burst tests stand for a type of testing that is used in every test standard and regulation as one of the key issues for ensuring safety in use. The central role of burst and proof test is grown to historical reasons for steam engines and steel vessels but - with respect for composite pressure vessels (CPVs) - not due an extraordinary depth of outcomes. Its importance results from the relatively simple test process with relatively low costs and gets its importance by running of the different test variations in parallel. In relevant test und production standards (as e. g. ECE R134) the burst test is used in at least 4 different meanings. There is the burst test on a) new CPVs and some others b) for determining the residual strength subsequent to various simulations of ageing effects. Both are performed during the approval process on a pre-series. Then there is c) the batch testing during the CPVs production and finally d) the 100% proof testing, which means to stop the burst test at a certain pressure level. These different aspects of burst tests are analysed and compared with respect to its importance for the resulting safety of the populations of CPVs in service based on experienced test results and Monte-Carlo simulations. As main criterial for this the expected failure rate in a probabilistic meaning is used. This finally ends up with recommendations for relevant RC&S especially with respect to GTR 13.
The presentation starts with the first agreement of making a national attempt for the introduction of a pV-limit for hydrogen transport. It explains aspects of the technical development, provides an impression of catastrophic incidents, and explains the difference between risk control and consequence limitation. Then the process of determining consequences and the result from the discussion at the UN-WG are explained. The next part summarises the approach for counting the number of impacted persons as a function of the model of pressure wave, the pressure peak, the limits of injured persons and the population density. Finally, the latest state of the discussion and the subsequent recommendations for a pV-value and the adequate phrases for explanation are introduced.
Dr Mair presents the competence centre “H2Safety@BAM”. He starts with a spectacular hydrogen accident on the Tempelhofer Feld (Berlin) in 1894, comes to the foundation of the competence centre in the context of the hydrogen strategies of Germany and the EU and explains their safety-focused orientation in order to create and maintain confidence in hydrogen technologies.
Beyond the long-term changes in energy supply, in Sept. 2022 there are enormous cost leaps in gas supply, which puts hydrogen as an energy carrier in a different light.
Based on this, he presents the structure of the Competence Centre with its 5 competence areas and the corresponding contact persons. This is underpinned by a slide on each of the work packages in the fields of competence.
At the end of the presentation, he explains the focus of the competence area "Component Testing, Component Safety and Approval", for which he is responsible. This is the question of cost reduction by using the whole potential of digitalisation in connection with the safety surveillance of the storage systems. The run of a fully digital system is of great importance for both, for the hydrogen supply of large consumers via road and rail and for storage systems in stationary plants. A robust and well-thought-out digitalisation in all levels of documentation will lead to a new quality in monitoring safety porperties, integration of new components and cost reduction.
Degradation and damage analysis of composite pressure vessels via experimental modal analysis
(2023)
For mobile gas storage systems, the application of type IV pressure vessels is state of the art. Type IV tanks consist of an inner polymer liner fully wrapped with fibre-reinforced plastic (FRP). Because of the complex fabric of the FRP as well as a difficulty estimable interaction behaviour between the single components under load, there are still no satisfying non-destructive testing methods to assess the current state of failure nor to estimate the level of degradation accurately and economically. At BAM division 3.5, analysing the ageing process of mobile composite pressure vessels is a major task to ensure safe usage over the whole lifetime. In this context, key aspects of our ongoing research activities are the invention of new test procedures and the development of accurate lifetime prediction models. In order to determine the level of degradation or damage, one meaningful non-destructive approach is to analyse the structural dynamic behaviour via an experimental modal analysis (EMA). Over the last few years, different types and sizes of composite pressure vessels have been tested in several research projects. The presented paper gives an insight into how to extract and interpret modal parameters and how to fit them to the results of residual strength tests.