III. 15 Integrity of Steel Welds in High-Pressure Hydrogen Environment (original) (raw)
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Hydrogen effect on fracture toughness of pipeline steel welds, with in situ hydrogen charging
International Journal of Hydrogen Energy, 2011
The API 5L X70 and X52 pipeline steel weld fracture toughness parameters are measured in a hydrogen environment and compared to the ones in air. The hydrogen environment is created by in situ hydrogen charging, using as an electrolyte a simulated soil solution, with three current densities, namely 1, 5 and 10 mA/cm 2. A specially designed electrolytic cell mounted onto a three-point bending arrangement is used and hydrogen charging is performed during the monotonic loading of the specimens. Ductility is measured in terms of the J 0 integral. In all cases a slight change in toughness was measured in terms of K Q. Reduction of ductility in the base metal is observed, which increases with increasing current density. A more complex phenomenon is observed in the heat affected zone metal, where a small reduction in ductility is observed for the two current densities (1 and 5 mA/ cm 2) and a larger reduction for the third case (10 mA/cm 2). Regarding microstructure of tested X70 and X52 base and HAZ metal, it is observed that the hydrogen degradation effect is enhanced in banded ferriteepearlite formations. The aforementioned procedure is used for calculating the fracture toughness parameters of a through-thickness pipeline crack.
Diffusible hydrogen in steel weldments - a status review
Despite being a subject of intense research and exclusive attention over the past several decades, hydrogen in the weldments of high strength steels continues to seriously limit the performance of the components and confounds the quantitative component prognosis. More than 1500 studies in the literature have reported the behavior and effects of hydrogen in steels and their welds. It is well documented that a sufficient amount of hydrogen, when combined with a crack susceptible microstructure and the weld residual stress, poses a greater risk of hydrogen assisted cracking (HAC). Cracking is undesirable in a weld because it causes a reduction in the mechanical properties, and thus poses a potential threat towards the structural integrity of the weldment. Of particular concern are the facts that HAC occurs at ambient temperatures, appears hours or days after the completion of welding and the cracks often remains undetected. Therefore, HAC may also cause catastrophic failure of a weld component while in service. It is known that the risk of cracking in welds can be reduced either by eliminating or by lowering at least one of the three following factors, the weld hydrogen content, the residual tensile stress and the crack susceptible microstructure of the weld, to levels below the critical to cause HAC. Reduction of hydrogen content in the weld is considered as the best way of reducing the risk of HAC. This can be achieved by employing dehydrogenation heat treatments to the steel and the weld. To choose a suitable dehydrogenation temperature, a knowledge of the hydrogen content in the weld is essential. Hydrogen in the steel weldments exists as diffusible and residual hydrogen. At a given temperature, while the residual hydrogen is permanently trapped in the weld and plays no role in HAC, the diffusible hydrogen is able to diffuse within or out of the weldment and is responsible for HAC. This brings out to the fore the need for the determination of diffusible hydrogen content in a weld. However, hydrogen is a transient element in steel and does not await its measurement like other elements. Therefore, development of a standard specimen and a standard procedure for the measurement of diffusible hydrogen is a daunting task. However, during the past few decades, several methods have been developed, tested and standardized for this purpose. This paper presents an overview of different aspects of hydrogen in steel welds and a systematic review of the different methods developed over the years for diffusible hydrogen measurement in steel welds.
Corrosion Science, 2012
The tensile properties of X52, X65, and X100 pipeline steels have been measured in a high-pressure (13.8 MPa) hydrogen gas environment. Significant decreases in elongation at failure and reduction of area were observed when testing in hydrogen as compared with air, and those changes were accompanied by noticeable changes in fracture morphology. In addition to baseline characterization of the effects of strength and microstructure on the X52, X65, and X100 alloys, the influence of strain rate and hydrogen gas pressure was studied for only the X100 alloy.
CONTROL OF HYDROGEN ASSISTED CRACKING IN HIGH STRENGTH STEEL WELDS
In present research work, the modified Granjon implant test was performed to evaluate the susceptibility of AISI 8620 and AISI 304 steel towards the hydrogen assisted cracking (HAC). Glycerine methods was employed to measure the diffusible hydrogen level (HD) in deposited metal for both the steels. The weld bead was deposited by using the Shielded metal arc welding (SMAW) process with basic type electrodes. The hydrogen was intentionally introduced for the plate of the material AISI 304 by using an oil of grade SAE 10, which is of very low viscosity. The fractured and un-fractured implant assembly were examined by using the field-emission scanning electron microscope (FESEM). The heat affected zone (HAZ) susceptibility is quantified by finding the lower critical stress (LCS) for a measured hydrogen content. The exact location of the fractures varied according to the type of materials being tested.
Hydrogen-Steel Compatibility Research at NIST-Boulder
2009
The NIST Materials Reliability Division is outfitting a high pressure (100 MPa) hydrogen testing facility to collect mechanical and thermodynamic property data on various candidate structural materials, and is developing data on nondestructive sensors that can measure the content of hydrogen in steels. These data are becoming extremely important as the economics of hydrogen transport drive the consideration of a range of conventional steels for storage and distribution of hydrogen, and the infrastructure grows beyond pilot plants and demonstration facilities. Preliminary results with X-100 pipeline steel show a 100-fold increase in fatigue crack growth rate when charged with hydrogen. The two nondestructive sensors being evaluated are based on thermoelectric power and eddy-current concepts. Both have been found sensitive to hydrogen contents of less than one part per million, and are being used to validate permeation measurements of hydrogen through various pipeline steels.
Hydrogen embrittlement susceptibility of a weld simulated X70 heat affected zone under H2 pressure
Materials Science and Engineering: A, 2014
The present paper deals with hydrogen embrittlement (HE) susceptibility of a weld thermal simulated heat affected zone of X70 structural steel in high pressure hydrogen gas at 20 1C. Fracture mechanics Single Edge Notched Tension tests at various hydrogen pressures (0.1, 0.6, 10 and 40 MPa H 2 ) have been carried out. The HE susceptibility was quantified through the measurement of the fracture toughness K Q and J (the effect of hydrogen pressure was addressed through linear load increase conditions till failure was obtained). The results show that hydrogen causes a strong decrease in the fracture toughness with increasing hydrogen pressure. The critical hydrogen pressure for the onset of HE was observed to fall between 0.1 MPa and 0.6 MPa. These results were supported by Scanning Electron Microscope (SEM) investigations of the fracture surfaces which showed a clear shift in the fracture mode at 0.6 MPa H 2 . Moreover, constant load tests were carried out in order to investigate the influence of hydrogen exposure time. The results imply that fracture always occurs within 8 h and that longer time to failure is related to stronger toughness reduction. This effect is more pronounced for test at 40 MPa than at 0.6 MPa hydrogen pressure levels. 3D Finite Element calculations of hydrogen diffusion have been performed and the results are discussed in relation to the experiments, in order to attempt to identify the hydrogen populations (diffusible or trapped) which act predominantly on the embrittlement of the material.
Strength, Fracture and Complexity, 2018
Hydrogen-Induced Cracking (HIC) is one of several related mechanisms whereby absorbed hydrogen atoms can compromise the integrity of components manufactured of low strength steels. A "low strength steel" is defined as having a maximum hardness of 22 HRC (249 HV). The corresponding maximum tensile strength is of the order of 800 MPa (116 ksi). Steels having localized areas with microhardness in excess of 22 HRC are particularly vulnerable to the development of HIC damage. HIC is a term applied to phenomena which occurs at low temperatures (typically less than about 90°C), and must not be confused with high temperature hydrogen attack of low strength carbon-manganese and low alloy steels exposed to hot hydrogen gas-containing environments. This review will highlight main factors that affect HIC development or failure by considering the following: (i) Metallurgical factors (effect of materials and microstructures), and (ii) Environmental exposure factors.