Providing resistance to sulfide stress corrosion cracking of pipelines welded joints by selection of welding parameters

Sulfide stress cracking (SSC) is one of the most dangerous types of pipelines destruction. Thermal impact of the welding process drives to heterogeneity of the microstructure and properties of the metal, which can lead to cracking of pipeline welded joints. Resistance to SSC of welded joints is determined by the thermal cycle of welding and cooling rate in the temperature range of austenite transformation. Due to performed studies based on simulation of welding heating the recommended range of cooling rates of 10–30 ° C/s was established, in which the resistance to SSC of welded joints is ensured. To calculate the cooling rates in coarse grained heat affected zone (CGHAZ) finite-element models of heat distribution were developed for longitudinal multi-electrode submerged arc welding (SAW) and multi-pass girth welding of pipes. Using the developed welding models, it was found that in order to achieve the cooling rate in CGHAZ it is necessary to reduce heat input up to 15-30% during multi-electrode SAW process of longitudinal welds of pipes . For multi-pass girth welding it is necessary to preheat the edges to be welded up to 100-300 °C depending on type of welding (GMAW or SMAW) and pipe wall thickness.