Welding Metallurgy of

The connection between hydrogen-enhanced plasticity and the hydrogen-induced fracture mechanism and pathway is established through examination of the evolved microstructural state immediately beneath fracture surfaces including voids, “quasi-cleavage,” and intergranular surfaces. This leads to a new understanding of hydrogen embrittlement in which hydrogen-enhanced plasticity processes accelerate the evolution of the microstructure, which establishes not only local high concentrations of hydrogen but also a local stress state. Together, these factors establish the fracture mechanism and pathway.

/pdf/hydrogen-embrittlement-understood-22elkmqzna.pdf

Hydrogen Embrittlement Understood

https://link.springer.com/content/pdf/10.1007%2Fs11663-015-0325-y.pdf

The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion

The effect of nanosized (Ti,Mo)C precipitates on hydrogen embrittlement of tempered lath martensitic steel

The microstructure and fracture morphology of AISI 8630-IN625 and ASTM A182-F22-IN625 dissimilar metal weld interfaces were compared and contrasted as a function of postweld heat treatment (PWHT) duration. For both systems, the microstructure along the weld interface consisted of a coarse grain heat-affected zone in the Fe-base metal followed by discontinuous martensitic partially mixed zones and a continuous partially mixed zone on the Ni side of the fusion line. Within the partially mixed zone on the Ni side, there exists a 200-nm-wide transition zone within a 20-μm-wide planar solidification region followed by a cellular dendritic region with Nb-Mo–rich carbides decorating the dendrite boundaries. Although there were differences in the volume of the partially mixed zones, the major difference in the metal weld interfaces was the presence of M7C3 precipitates in the planar solidification region, which had formed in AISI 8630-IN625 but not in ASTM A182-F22-IN625. These precipitates make the weldment more susceptible to hydrogen embrittlement and provide a low energy fracture path between the discontinuous partially mixed zones.

Microstructure and Hydrogen-Induced Failure Mechanisms in Fe and Ni Alloy Weldments

The need to use strain-based design is growing due to approaching pipeline projects in challenging environments including permafrost, offshore ice hazards, active seismic areas, and in high temperature/high pressure operations. This has stimulated significant research and development efforts in industry, and some of the work is making its way into design codes and industry projects. To ensure pipeline integrity and overall cost effectiveness, a strain-based design approach needs to consider all key interrelated design aspects, including strain demand, design methods, material selection, strain capacity validation, and impact on construction and operation. This paper examines some of these key considerations and recommends practices for engineering and execution of strain-based pipelines. It also includes a discussion of strategies for projects to minimize strain demand, including monitoring and mitigating high strain locations as they develop in the pipeline during operation. The paper highlights ExxonMobil’s effort in design, testing, model development, and project applications to advance and enhance the capability of strain-based pipeline applications.

Strain-Based Pipelines: Design Consideration Overview

The aim of this first symposium on strain-based design of pipelines was to bring together a multidisciplinary group of industry experts to discuss the challenges of designing pipelines subjected to high strain. The symposium included nearly fifty presentations and comprehensive proceedings covering all aspects of strain-based design. This review summarizes the key themes of the symposium including projects, design, mechanics, assessments, materials, and testing. The work presented at the symposium shows the broad range of efforts underway to address the challenges of strain-based design of pipelines as well as the work remaining to be completed to have an industry-wide consistent solution. Rather than simply providing a compilation of these various studies, this review aims to assess the work within each topical area collectively. This assessment of the state of the art and remaining challenges from the symposium will serve as a backdrop for the Second (2008) ISOPE Strain-Based Design Symposium.

The First (2007) ISOPE Strain-Based Design Symposium - A Review

Hydrogen Effects on the Failure Mechanisms in Fe-Ni Weldments

Pipeline engineering and construction are migrating towards installations in remote and potentially harsh environmental locations. Traditional stress based designs (strain demand < 0.5%) are typically inadequate or improper for regions with seismic activity, soil movements, liquefaction, and arctic regions with potential frost heave, thaw settlement, and ice scour. This paper reviews specific design and testing methodologies for the qualification of welding procedures for high strain applications. These methods have been applied in the development and qualification of welding procedures for the construction of pipelines subject to longitudinal tensile strains in excess of 2%. The transition from elastic to plastic design requires considerable effort in terms of qualification and testing requirements. These testing requirements may include the need for full scale pressurized testing for design validation. The cost and effort associated with complex qualification programs provides motivation for the development of analytical tools which can lead to streamlined test programs. The status of such efforts within ExxonMobil will be briefly described.

Dan B. Lillig

Papers

Microstructure and Hydrogen-Induced Failure Mechanisms in Fe and Ni Alloy Weldments

Strain-Based Pipelines: Design Consideration Overview

The First (2007) ISOPE Strain-Based Design Symposium - A Review

Hydrogen Effects on the Failure Mechanisms in Fe-Ni Weldments

Welding Engineering For High Strain Pipelines