Weldability evaluation of supermartensitic stainless pipe steels

Significant interest exists in the use of supermartensitic materials for oilfield applications. However, the hardness for both the weld deposit and the heat-affected zone (HAZ) of different material combinations may exceed the NACE requirement of 23 HRC (253 HV). Therefore, further studies to quantify the mechanical properties of welded joints and variables controlling the sulfide stress cracking (SSC) resistance in the as-welded condition remain necessary both for economical fabrication and to ensure reliable service operation. In this program, the aswelded mechanical properties of three different supermartensitic pipe steels were compared using different welding consumables and welding procedures. The susceptibility to hydrogen-induced stress corrosion cracking of selected weldments under slightly sour conditions and under cathodic protection was evaluated. Additionally, the influence of short postweld heat treatment (PWHT) on the HAZ mechanical properties and on the microstructure of three supermartensitic stainless pipe steels was studied. The results show that the filler metal and welding procedure combination affect the matching characteristics of the welded joint and their toughness and ductility properties. Additionally, supermartensitic steel welded joints with a maximum hardness ranging from 282 to 313 HV1 and under an applied stress level equal to the measured yield strength of the base material did not crack under slightly sour conditions. The result also showed that a short PWHT is effective in reducing the micro-hardness of the HAZ to levels very close to the hardness of the base metal in the as received condition. It is assumed that the main mechanism responsible for the changes of hardness with PWHT is the amount of reverted and stable austenite.