P8 themocouple to attach to B31.3 P5B heater pipe

[Naidooru]

Hi all,

Please advise on the following. for all reference this is in accordance with B31.3 2012
I have a furnace tube of material specification P5B
The user needs to attach a thermocouple via fillet weld of 3mm to the outside of the tube of which the material is a P8 stainless steel.
The table 331.1.1 says that all weld sizes are mandatory under P5B material specification but in paragraph 331.1.3 (2) says that for P-No 3,4,5 & 10A when weld throat thickness is less than 13mm PWHT is not mandatory as long as the minimum preheat is applied. Please advise if i am reading this correctly and if it applies to P5B material.

Kind regards

Ruben Naidoo
Senior Inspector of Pressure Equipment
SAPREF Refinery SA (SHELL & BP)

 

[srijey]

Attachment welds heat treatment requirement is strictly based on metallurgical requirements and not service requirements. Hence, if your fired heater coils are designed as per B31.3 older version (2015 edition mandates PWHT for all P5B), then you must stick to that standard. These PWHTs are referring to attachment welds which are mostly fillet or partial penetration welding less than 10mm From tempering and residual stress point of view, personally I do not feel any benefit on PWHT of this attachment weld.. Stick with the preheat and weld PQR requirements and that would do. Even the thermocouple manufacturers can share such experience with you - never heard of any failure due to residual stress or tempering on P5B thermocouple attachment welds - whether Vpad, plain pad or just sheath welds. Just in case you happen to weld with less heat input using the methods suggested in UCS-56, you don't need PWHT.The short answer to your question is - Yes, you don't need PWHT with 2012 version of 31.3.

Regards

jey