preheat & post weld heat treatment of SA-387 Gr 11 Class 2 ( 1 1/4 Chrome-moly) material 2

[orion952]

What is required for preheating and post weld heat treatment of 1 1/4 Chrome-moly material?

 

[stanweld]

To what Code?

 

[orion952]

ASME Section VIII Div 1!

 

[SnTMan]

orion952, see Part UCS

Regards,

Mike

 

[orion952]

I understand Section UCS covers the post weld heat treatment requirements. My concern is any required preheat for welding and if that preheat has to be maintained until the weldment enters the furnace for PWHT. This I undersatnd has been required or recommended for certain chrome-moly grades to prevent cracking of the welds. I am trying to find out if SA-387 Grade 11 class 2 material requires such continuous preheat until PWHT starts.

 

[SnTMan]

orion952 Part UCS does specifiy pre-heat under some conditions, but to my experience maintaining pre-heat thru PWHT is not needed for 1 1/4 Cr materials. More commmon with 2 1/4 Cr.

Do not take this as definitive, your weld procedures, your service, your job specs (if any) may require different.

I doubt Sec VIII, Div 1 is going to require maintenance of pre-heat in any case, I think it is going to be mandated by metallurgy and desired properties.

Regards,

Mike

 

[stanweld]

Preheat maintenance is not required. Preheat should be 250 F min - 300F recommended. If welding is interrupted, recommend slow cooling under insulation for T > 1/2". Greater adherence to preheat is mandated as thickness and joint restraint increase. Hydrogen embrittlement can and will occur if you do not appreciate the need for preheat.

 

[jtseng123]

I purchased a reactor last year for the same materail except it is class 1, ready to ship. Here is the requirement:

"Welded joints shall be heat treated immediately upon completion of welding.
The joint shall not be allowed to cool below 300 ºF (150 ºC) prior to heat
treatment. Alternately, the weld and adjacent metal may be heated to 600 ºF
(315 ºC), wrapped with insulation, and allowed to cool. Heat treatment may
then be performed later. "

The other source is API 934-E (1 1/4Cr-1/2Mo for above 825F), para 7.3.1 stating " During welding, the preheat temp shall be maintained until PWHT or dehydrogenation heat treatment (DHT) is performed in accordance with 7.3.2".
7.3.2 saying DHT to be 570F minimum for one hour minimum.

 

[orion952]

Ok, now I have conflicting recommendations. the only difference is I have class 2 material, not class 1 and my design temeperature is 250 F for one vessel and 650 F for the second vessel.

 

[jtseng123]

If your vessel is in high pressure hydrogen service, check API 934-C for below 825F service. It has the same statement as 934-E. Both class 1 and 2 make no difference on preheat and PWHT requirements, only material properties are different as I understand.
Years ago we had vessel ordered as class 2. However, the tensile and yield failed to meet the values, and re-certified as class 1.