PR-350-124504-R03 Essential Welding Variables Methodology for X70 Linepipe Steels

High productivity mechanized welding processes, such as variants of multi-wire pulsed-gas metal arc welding (GMAW-P) have become increasingly popular due to their high production rates. Compared to conventional single-wire/single-torch GMAW processes, the higher productivity variants of the GMAW processes are more complex in welding procedure design, qualification, and field welding, which leads to more complex heating and cooling cycles. As a result, the deposited weld metal and heat-affected zone (HAZ) performance can be quite different from those from more traditional welding processes applied to the same materials. These changes have not been adequately considered and incorporated into essential welding variables in codes and standards.

The objective of this project is to validate the essential welding variable methodology (EWVM) for welding of X70 line pipe steels by modern, high-productivity pulsed-gas metal arc welding (GMAW-P) techniques to achieve desired weld properties while keeping the cost and time needed for welding procedure qualification to a minimum. Four girth welds with various combinations of heat input and torch configurations were made using GMAW-P. The microstructure response and mechanical properties of weld metal and/or HAZ by testing thermally simulated weld and pipe steel base metals were analyzed. Correlation of welding parameters and thermal history was summarized. The application of EWVM is briefly presented in a step by step procedure. The girth weld properties demonstrate the sensitivity of thermal cycles and the ability of EWVM to predict the trend of the properties. In the long run, welding procedure qualifications focusing on the control of cooling rate could allow a reduction in the number of essential variables.