Development of HAZ Hardness Limits for In-Service Welding

Overview

Main Objective

The objective of the proposed project is to develop heat-affected zone hardness acceptance criteria that can be used to evaluate welds during the qualification of procedures for welding onto in-service pipelines.

Public Abstract

Welds made onto in-service pipelines are particularly susceptible to hydrogen cracking. During qualification of welding procedures, limits are often imposed on heat-affected zone hardness (e.g., 350 HV max.) as a way to avoid cracking. The hardness level below which hydrogen cracking does not occur is not a fixed value, but varies as a function of several parameters. The results of previous work resulted in the development of hardness evaluation criteria that can be used to quantify the trade-offs that can be made between HAZ hardness, hydrogen level, and the chemical composition of the materials being welded for welds made onto in-service pipelines. Further development and validation is required prior to the widespread use of these criteria, particularly for microalloyed materials used for modern high-strength pipelines. The use of these criteria will reduce the cost and increase the reliability of pipeline modifications and repairs. The project will be conducted by a team consisting of CC Technologies and University of Wollongong (UoW).

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