Post weld heat treatment of welded low alloyed steel pipes : Use of AISI 4130 steel in hydrogen sulfide environment and its post weld heat treatment conditions

Abstract

Based on the results from pre-projectand workcovered by this thesis, no better alternatives to AISI 4130 material was found, neither could it be safely concluded for removal of NACE MR0175/ISO 15156 requirementsin any parts of high-pressure drilling fluid system. SinceAISI 4130 hasshown to be the optimal choice for the system,it was decided to look forimprovementsof welding procedure by optimization ofpost weld heat treatmentforthis steel.Heat treatment is an expansive and time-consuming procedure that,if not done correctly,could weaken the materialand jeopardize the safetyof the system.Inthis thesis, whith the help of theoretical research, experimental heat treatment and microscopyanoptimal temperature of 650 °C with holding time of 150 minutes wereproposedfor PWHT of AISI 4130 steel pipes.It is further suggested to look into increasing of preheatingand interpass temperature to maximum allowed value of 250 °C, which is expected toreduce cooling rate,allowing for less brittle and tougher material structure.This thesis includespreparation and examination of test pieces, including hardness test and microscopy. Thus giving a good foundation forthe developmentofa welding procedure for AISI 4130 pipe