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kissjxp (Materials) (OP)
27 Jun 08 15:01
Dissimilar welding of p1 to P8 materials for a pressure vessel (ASME VIII div.1), plate thickness is 40mm.

(1) If materials are used for pressure parts, what is the preheat temperature I can use? Can I do PWHT for them?

(2) If materials are used for Non-pressure part, what is the preheat temperature I can use? Is PWHT required by code?

ASME VIII div.1 is used for the pressure vessel construction.

Please advise. Thanks.
unclesyd (Materials)
27 Jun 08 15:13
Normally you would not us preheat for welding P1 to P8 unless there was a thickness concern.

Comeback with the specific materials and thicknesses.  
kissjxp (Materials) (OP)
27 Jun 08 16:33
In ASME VIII div.1, if the thickness of carbon steel plate is greater than 32 mm, a preheat temperature of 200F is recommened. I was wonderting whether or not to apply a preheat of 200F for the dissimalar welding of P1 material to P8 material.
metengr (Materials)
27 Jun 08 18:52
What is the actual thickness of the CS base material (P-No 1) at the weld joint??????
kissjxp (Materials) (OP)
27 Jun 08 22:54

Pressure containing base metal: 34mm

Non-pressure containing base metal: 48mm

metengr (Materials)
28 Jun 08 9:51


In ASME VIII div.1, if the thickness of carbon steel plate is greater than 32 mm, a preheat temperature of 200F is recommened

You have found your preheat requirement answer above for pressure retaining carbon steel material used with similar material or in a dissimilar metal weld (DMW) joint application (See Table UCS-56 in Section VIII, Div 1). The key is to set a maximum interpass temperature of 400 deg F for use in a DMW to avoid exposing the P-No 8 to high heat input.

For non-pressure retaining CS material that is welded to non-pressure retaining austenitic stainless steel, this advice would still hold for the CS and thickness. I like to use ASME Section VIII, Div 1 preheat requirements even for non-pressure retaining applications to remain consistent.
kissjxp (Materials) (OP)
29 Jun 08 11:15

Would you recommend the PWHT for the non-pressure carbon steel? Is ASME VIII Div. 1 UCS56 applicable for Non-pressure part?

metengr (Materials)
29 Jun 08 11:35
No, as long as a preheat is used and you follow Table UCS-56 for thickness exemptions for PWHT. This table can be used for non-pressure parts.
kissjxp (Materials) (OP)
29 Jun 08 12:27
The non-pressure part thickness is 48mm. Based on Table UCS-56, PWHT is required. Right?

metengr (Materials)
29 Jun 08 12:50
If the non-pressure part is P-No 1 material and exceeds 38mm in thickness, PWHT would be required. Now, if you are going to be welding this to a P-No 8 base material in a DMW joint, you should butter the P-No 1 weld joint with 309, PWHT the P-No 1 base material after buttering, and complete the weld joint using 308 stainless steel with no PWHT.
kissjxp (Materials) (OP)
29 Jun 08 13:35

Thanks for you helpful advice.
KimBellingrath (Mechanical)
6 Aug 08 16:18
Does anyone know of a quick reference guide to the 'P' numbers and what material they represent?
unclesyd (Materials)
6 Aug 08 16:35
This is about the quickest you can get.
Mr168 (Materials)
6 Aug 08 16:50
Just in case you miss the link on the C-Spec site, its

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