Thermocouple Requirement for PWHT
For PWHT of pipe, what is the minimum requirement of Thermocouple with respect to diameter and according to which clause of the relevant Code/Standard.
If one element is used to carry out PWHT of 4-6 scattered weld joints of small bore then only one thermocouple is sufficient OR not to represent all joints.
Most components shall have 3 separate locations for thermocouple placement. 1) centerline of weld, 2) edges of soak band (SB) and 3) edges of heated band (HB). For NPS 8 and less it usually is 1 TC at 12:00 for weld centerline, monitoring at 6:00 at both edges for the SB, and monitoring at 12:00 for both edges of the HB. Based on the thickness,diameter and space between the scattered joints, PWHT temperature and material,One TC would not be a proper representation of all weld joints. The owner should have a Operating Procedure to address PWHT requirements.
