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Eingeladener Vortrag
- nein (43)
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 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.