Post weld heat treatment 2.25 Cr - 1 Mo

[metaal]

What are the effects of several (5 times) heat treatments on a tubesheet material SA336 F22 Cl3 (with Inconel cladding )and tubes SA 213 T22 material.

Tubesheet is PWHT-ed in the furnace after welding the Inconel cladding.After this 4 local heat treatments are executed due to repairs.

After first repair a test is done and the hardness on the HAZ of tube was after one cycle 193 HV10 after 2 cycles 221Hv10.

In the ASME code any restriction of heat treatment cycles is made. Can this be accepted ?

 

[QC1971]

I would start by reviewing your Welding Procedure Qualifications (PQR) to see if they support your total time at temperature as QW-407 of SEC IX applies to your situation.

 

[metengr]

The number of PWHT's that you indicated concerns me in terms of maintaining the specified tensile and yield strength requirements if this is Class 3. When the WPS was qualified, did you simulate multiple PWHT cycles or consider the total PWHT time? If not, you need to run a coupon and determine if multiple heat treatment cycles will adversely affect your mechanical properties.

 

[metaal]

Thanks for the info.

During PQR qualification the testcoupon is PWHT after weld overlay and one PWHT cycle after welding tube-tubesheet.

At this moment we remove all welds and will reweld the tube-tubesheet joint. A new local PWHT will be done. But like metengr mentioned, I'm worried about mechanical properties and since mixture of both mediums is not allowed and design pressure is 230 bar we have to be careful.

Is it correct that the only restriction of PWHT cycles are the mechanical properties ? (also ASME IX QW407)

 

[ijzer]

You have to check your material certificate of the tubesheet material.
Was this material ordered including simulated PWHT and at what time and temperature. Actual total time shall not go over the simulated test time. See also UCS-85

 

[stanweld]

metaal,
It is not surprising that the hardness values increased after the 2nd PWHT. Temper embrittlement and hardening due to carbide precipitation has been well documented with this alloy. I do not suspect that Tensile/Yield will decrease below that of the base metal specification but %elongation may be. Impact toughness properties will be adversely affected. Please note that if you cladded by Weld Overlay your procedure will no doubt require requalification (ref. QW-407.6)

 

[metaal]

According to material test certificate :
one austenitize (1742°F/8h) and tempering (1310°F/12h)
4 max PWHT cycles : 1274°F time 8h.

At this time the actual time is 20h. This is less than 32h.