Evaluation of proportion of phases in joints welded from duplex stainless steel pipes by means of non-destructive testing

Abstract

Duplex stainless steels (DSSs) combine excellent corrosion resistance and high mechanical strength, due to the fine two-phase microstructure composed of similar amounts of ferrite (δ) and austenite (γ). These alloys are used in piping and industrial equipment for which a high strength-to-weight ratio is required, especially in building construction and off-shore assembly. However, welding operating conditions can promote a significant microstructural imbalance of these phases, resulting in a decrease of the properties cited above. Evaluation by feritscope is normally used in these activities. During evaluation with a feritscope, the welded joint may be rejected when the weld metal is found to have ferrite values outside of the range established by project specifications. Thus, analysis of these joints is important, along with complementary techniques such as the use of metallographic replicas. This study aimed to evaluate the proportion of phases in relatively thin spools of DSS, welded in the field, comparing the non-destructive techniques described. The results show similar values, yet the result may be influenced by the shape and surface conditions of the welded joint.

Keywords::

• duplex stainless steel
• welding
• non-destructive testing
• magnetic properties
• metallographic replica