Piping Material

One way is to check in the ASME B31.3 code - Section 331 Heat Treatment

I don't feel like reiterating the Tables from B31.3 but I will offer this much -

Mild Carbon Steel (P-No. 1) less than or equal to 3/4" wall thickness at all tensile strength of base material does not require post weld heat treatment.

Or perhaps the applicable welding procedures that you (hopefully) are following.

Also, according to ASME B31.3, Table 331.1: For carbon steel piping material P.No. 1 & Group No. 1, with thickness > 20 mm (3/4 inch):

Heating Metal Temp.: 593-694 ^oC (110-1200 ^oF).

Holding Time: 2.4 min./mm (1 hr/inch) with a min time of 1 hr.

After you read this, post your further questions and others may respond.

http://www.barc.ernet.in/webpages/letter/2003/200310-17.pdf

best regards.

milo

As stated B31.1 and B31.3 give recommendation's also boiler code, Sec VIII, and Sec III, AWS D1.1 give rules for PWHT.

There are code required PWHT for material and for service. The alloy steel often require PWHT as well as Preheat. Your P91, P22, P11 materials most often require PWHT with some allowances for not doing a PWHT cycle if certain criteria are met, wall thickness, correct preheat applied during welding, diameter of the pipe.

Carbon steel over 3/4" may require PWHT, depending on the service and PQR of your welding technique.

Hold times, temperature, rate of heating and cooling, and desired hardness ranges are again listed in your various codes. depending on service, material, and code.

What are you building, designing, and what is the service? With a bit more information we maybe able to help you. However, all depends on the code, PQR, WPS.

The reasons that we PWHT are to improve ductility, reduce hydrogen inclusion, improve creep failure, soften the Heat Affected zone (HAZ).

We always use 3/4" as a starting point for PWHT on carbon steel. I think in some circumstances you are allowed to go to 1" before PWHT is required on carbon steel though. One thing to remember is that if your have to do PWHT by ASME code your WPS (welding procedure specification)and PQR (Procedure Qualification Record)will have to have PWHT listed on them. Also you will generally have a base metal pre heat required as well for most alloys. I sometimes use an alternative method to PWHT on thick vessels where we are replacing a small nozzle or doing another small amount of welding. It basically has a higher pre heat and lower inter-pass temps and also a stringer half bead welding technique. The Authorised Inspector must know and approve all the welding specs for using this alternative method ahead of time where I am located.

pipewelder