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To increase the competitiveness of jacket substructures compared to monopiles a changeover from an individual towards a serial jacket production based on automated manufactured tubular joints com-bined with standardized pipes has to be achieved. Therefore, this paper addresses fatigue tests of automatical-ly welded tubular X-joints focusing on the location of the technical fatigue crack. For this X-joint, the detect-ed location of the technical crack is then compared to numerical investigations predicting the most fatigue prone notch considering the structural stress approach as well as the notch stress approach. Additionally, the fatigue prone hot spot according to both approaches is compared for a typical offshore jacket double-K-joint to emphasize the significance of the presented outcomes for the existing offshore structures. Besides, the welding process of the automated manufactured tubular X-joints is presented.
At the Stakeholder meeting of the EMPIR project “Multifunctional ultrafast microprobes for on-the-machine measurements”, details about two measurement modes were presented. Force distance curves and contact resonance measurements are compared. The basic principles are explained and exemplary measurements concerning mechanical properties of polymers are shown.
Um ein tieferes Verständnis über die Schallemission bei der Entstehung und Ausbreitung von Rissen in Stahlrohrleitungen zu erlangen, wurde ein Stahlrohr der Güte S355J2H im Vierpunkt-Biegeversuch quasistatisch bis hin zum Wanddurchbruch (Leckage) belastet und mittels Schallemissionsmessung und Gleichstrompotentialmessung überwacht. Das Rohrsegment wurde durch einen 90°- Außenumfangskerb in der Mitte der Rohrlänge definiert vorgeschädigt, um davon ausgehend ein stabiles Risswachstum zu induzieren und die Analyse von Schallemission aus Rissereignissen, die am Kerb eintraten, sicherzustellen. Für die Schallemissionsmessung wurden vier Breitbandsensoren max. 105 mm vom Kerb entfernt montiert. Die Signalaufzeichnung erfolgte kontinuierlich und schwellwertunabhängig. Für die Gleichstrompotentialmessung wurde ein Gleichstrom von 300 A eingeleitet und der Potentialabfall über dem Kerb mit fünf Sonden entlang des Kerbs gemessen. Beide Messverfahren identifizieren die Rissinitiierung sowie Veränderungen im Risswachstum. Die detektierten Schallemissionsereignisse werden, unter Berücksichtigung spektraler Eigenschaften, mit fortschreitender Belastung und Rissentwicklung analysiert. Diese Studien wurden im Rahmen des interdisziplinären Forschungsprojekts AGIFAMOR, Aging infrastructure - Faseroptisches Monitoring von Rohrleitungen, an der BAM durchgeführt.
The development of hydrogen technologies is a key strategy to reduce greenhouse gas emission worldwide. Power-to-Gas is a challenging solution, in which hydrogen and methane can be used in mobility, industry, heat supply and electricity generation applications. This presentation deals with the tribological behaviour of polymer materials in hydrogen and methane, both in gas and in liquefied form.
Das Plasma-Pulver-Auftragschweißen ist ein Verfahren, dass hohe Auftragraten ermöglicht, jedoch auch eine erhöhte thermische Belastung des Bauteiles verursacht. Laser-Pulver-Auftragschweißen hingegen erreicht eine hohe Präzision und eine geringe Aufmischung, erfordert jedoch ein kostspieliges Hochleistungslasersystem und erreicht im Vergleich nur geringe Auftragraten, was zu hohen Verarbeitungskosten führt. Eine Kopplung von Laser- und Lichtbogenenergie in einer gemeinsamen Prozesszone zielt darauf ab, die jeweiligen Vorteile beider Technologien zu nutzen. Dies betrifft insbesondere die Effizienz der Wärmeausnutzung und der Nutzung des Zusatzwerkstoffs.
Es wird ein Plasma-Laser-Hybrid-Prozess als Highspeed-Plasma-Laser-Cladding-Technologie (HPLC) für Beschichtungs- sowie Instandsetzungszwecke vorgestellt. Gezeigt werden Ergebnisse mit Prozessgeschwindigkeiten von 10 m/min bei Laserleistungen von 2 kW, dabei können Flächenraten von mehr als 1 m2/h erreicht werden. Effiziente Beschichtungen von großen Flächen, beispielsweise auf rotationssymmetrischen Bauteilen stellen ein relevantes Anwendungsfeld für diesen Technologieansatz dar. Die Nickelbasislegierung Inconel 625 wird als Korrosionsschutzwerkstoff eingesetzt. Im Rahmen der Verfahrensprüfung werden die hergestellten Beschichtungen einer EDX Messung unterzogen.
Prozesscharakteristische Kenngrößen wie z.B. die Auftragrate werden vorgestellt und vor dem Hintergrund wirtschaftlicher Kennzahlen diskutiert. Zusätzlich werden die Aufmischung, Spurgeometrie und Wärmeeinflusszone der Spuren und Schichten ausgewertet. Im Vergleich zum Laser-Pulver-Auftragschweißen werden Spuren bei hohen Prozessgeschwindigkeiten mit einer hohen Auftragrate erzeugt.
Rapid cooling rates and steep temperature gradients are characteristic of additively manufactured (AM) parts and important factors for residual stress formation which have implications on structural integrity. This study examined the influence of heat input on the distribution of residual stresses in two prisms produced by laser powder bed fusion (L-PBF) of austenitic stainless steel 316L.
The layers of the prisms were exposed using two distinct helix scanning strategies: one scanned from the centre to the perimeter and the other from the perimeter to the centre. Residual stresses were characterised at one plane perpendicular to the building direction at half of its build height using neutron diffraction. In addition, the defect distribution was analysed via micro X-ray computed tomography (µCT) in a twin specimen.
Both scanning strategies reveal residual stress distributions typical for AM: compressive stresses in the bulk and tensile stresses at the surface. However, temperature gradients and maximum stress levels differ due to the different heat input. Regarding the X-ray µCT results, they show an accumulation of defects at the corners where the laser direction turned through 90°.
The results demonstrate that neutron diffraction and X-ray µCT can be successfully used as non-destructive methods to analyse through-thickness residual stress and defect distribution in AM parts, and in the presented case, illustrate the influence of scanning strategies. This approach contributes to deeper assessment of structural integrity of AM materials and components.
9 %-Cr steel P91 is widely used in power plants due to the excellent creep-resistance. Components of this steel are typically welded and demand for careful welding fabrication, whereas a so-called post weld heat treatment (PWHT), must be conducted to increase the toughness and decrease the hardness of the martensitic as-welded (AW) microstructure. Before the PWHT, a hydrogen removal (or dehydrogenation) heat treatment is necessary as hardened AW martensitic microstructure is generally prone to delayed hydrogen assisted cracking (HAC). The microstructure and temperature dependent hydrogen diffusion is an important issue as it determines how long a potential crack-critical hydrogen concentration could remain in the microstructure. In this context, reliable hydrogen diffusion coefficients of P91 weld metal are rare. Hence, the diffusion behavior of P91 multi-layer weld metal was investigated in two different microstructure conditions: AW and further PWHT (760 °C for 4 h). Two different experimental techniques were used to cover a wide range of hydrogen diffusion temperatures: the electrochemical permeation technique (PT) at room temperature and the carrier gas hot extraction (CGHE) for a temperature range from 100 to 400 °C. From both techniques typical hydrogen diffusion coefficients were calculated and the corresponding hydrogen concentration was measured. It was ascertained that both heat treatment conditions show significant differences in hydrogen diffusivity. The biggest deviations were identified for room temperature. In this case, the AW condition shows significant hydrogen trapping and up to seven times lower diffusion coefficients. Additionally, PT investigations showed a preferred diffusion direction of hydrogen in the weld metal expressed by the diffusion coefficients and the permeability for both heat treatment conditions. The CGHE generally revealed lower diffusion coefficients for the AW microstructure up to 200 °C. In addition, the AW condition showed hydrogen concentrations up to 50 ml/100 g (considering electrochemical charging). Nonetheless, this hydrogen was not permanently (reversibly) trapped. Nonetheless, this temperature is approximately 100 °C below recommended dehydrogenation heat treatment (DHT). This has two main consequences: (I) in case of welding is interrupted or no DHT is conducted, a HAC susceptibility of hardened martensitic P91 weld metal cannot be excluded and (II) DHT can be conducted at temperatures around 200 °C below the recommended temperatures.
9 %-Cr steels like P91 and P92 are widely used in power plants due to the excellent creep-resistance. Components of this steel are typically welded and demand for careful welding fabrication, whereas a so-called post weld heat treatment (PWHT), must be conducted to increase the toughness and decrease the hardness of the martensitic as-welded (AW) microstructure. Before the PWHT, a hydrogen removal (or dehydrogenation) heat treatment is necessary as hardened AW martensitic microstructure is generally prone to delayed hydrogen assisted cracking (HAC). The microstructure and temperature dependent hydrogen diffusion is an important issue as it determines how long a potential crack-critical hydrogen concentration could remain in the microstructure. In this context, reliable hydrogen diffusion coefficients of P91 and P92 weld metal are rare.
Hydrogen was once called “the versatile embrittler” [1], which summarizes very well the effect on reduction of ductility and/or toughness in technical alloys like steel. In that connection, welding is one of the most important component fabrication technologies. During welding, hydrogen can be transferred to the weld pool from manifold sources (like contaminations, residuals at the surface, etc.). As hydrogen embrittles a material, the safety of welded components with hydrogen is always a critical issue. Weld heat input causes additional changes in the microstructure like grain growth or partial dissolution of precipitates and many more. All these things influence the mechanical properties and also represent hydrogen traps. These traps decrease the hydrogen diffusion compared to the ideal lattice. The result can be so-called delayed hydrogen assisted cracking (HAC) of the weld joint due to the significantly decreased diffusivity by trapped hydrogen. This is often an underestimated risk as those cracks can appear in the weld joint even after some days!
It is essential to know about hydrogen ingress during welding and the microstructure specific hydrogen diffusion. Both are depended on weld parameter influence and the chemical composition of the base material and weld metal. For that purpose, gas analytic methods like solid-state carrier gas hot extraction (CGHE) are useful tools to: (1) identify detrimental hydrogen concentrations from weld joints, (2) binding energies from hydrogen traps by thermal desorption analysis or (3) high-temperature diffusion coefficients. Those values are extremely important for welding practice in terms of recommendations on realistic hydrogen removal heat treatment (HRHT) after welding. Considering the increasing use of “digital” experiments, the data is also needed for reliable numerical simulations of HAC process or HRHT-effectiveness.
The present contribution gives an overview on the influence of hydrogen on weld joints, the necessity, methods and standards for hydrogen determination (CGHE) with the aim of fabrication of safe welded and crack-free components.
[1] R. A. Oriani (1987), Corrosion 43(7):390-397. doi: 10.5006/1.3583875
Als Ausgangspunkt für i-TRIBOMAT schließen vier renommierte Institutionen in Europa, darunter die BAM, ihre Test- und Analytik-Methoden zusammen. Es entsteht ein Testfeld aus weit über 100 Tribometern mit den entsprechenden, analytischen Kapazitäten. Alle Ergebnisse fließen in eine harmonisierte Datenbank, die tribologische Erkenntnisse mit Materialeigenschaften ebenso zugänglich macht, wie Hinweise auf ökologische und gesundheitliche Verträglichkeiten. Diese Datenbank bildet zusätzlich das Rückgrat einer Vielzahl von Modellierungsmethoden, die die Entwicklungszeiten von der Idee bis zum marktreifen Produkt deutlich verkürzen sollen. Alle diese Möglichkeiten sollen über eine europaweit agierende, zentrale Kontaktstelle zur Verfügung gestellt werden.