L52351 Microstructure and Properties of Simulated Weld Metals - Optimized Welding Solutions for X100 Pipe

This investigation is part of a major consolidated program of research that was launched to address key research gaps related to welding of high strength pipe which is an integral part of pipeline design and construction. The two research focus areas include (i) update of weld design, testing, and assessment procedures and (ii) development of optimized welding solutions for high strength steel X100 line pipe. In the second focus area, physical simulation techniques were used to study both weld metal (WM) and heat affected zone (HAZ) regions for a range of compositions and thermal cycles relevant to various welding options being considered for high strength steel (X80 and X100) pipes. The results of the WM and HAZ studies are reported separately. These complementary investigations were intended to provide improved understanding and information necessary to establish guidelines for development of welding procedures for demanding applications. The work was:

To characterize the WM microstructure and hardness for a series of experimental plate welds produced with two distinct welding procedures using single and multipass welding techniques,
To apply thermal simulation techniques to develop WM CCT diagrams for a range of compositions applicable to welding of X100 pipe to serve as a tool for predicting their respective transformation behaviours, and
To provide an assessment and comparison of notch toughness properties for a range of single thermal cycles.

Benefit: The short term benefit of this consolidation ensured that technology development occurred in an informed, almost holistic manner. Having a single coordinated core research team addressing many of the interrelated issues involving the welding of high strength steel pipelines created synergies and depth in problem solving that would not have developed with the original independent project structure. The long term benefit is in the technology that delivers solutions in key areas:

Proposed specifications for high strength line pipe properties for different grade classifications considering the needs of both stress based and strain based designs;
Alternative tensile test protocols for more consistent strength measurement in narrow groove pipe welds;
Small-specimen toughness test protocols for the assessment of weld metal and HAZ;
Small-, medium, and large-scale tests that support pipeline design requirements;
Weld integrity assessment procedures for various design requirements (stress- vs. strain-based design); and
Optimized welding solutions for X100 line pipe steel.
Reassessment of welding essential variables in terms of the factors directly influencing weld properties that can be applied to improve reliability and consistency for any pipe grade.

Because full benefit is achieved through changes to applicable codes and standards, work product was developed in a manner to facilitate acceptance by codes and standards organizations.