ASME B31.3 PWHT Requirement 3

[algerdj]

My company is welding 18" Schedule 60 carbon steel pipe (nominal pipe wall thickness of 0.750") and per B31.3 Table 331.1.1 this would be exempt from PWHT.

I know that there is tolerance on the pipe wall thickness, if I remember correctly it is ±12.5% of nominal.

My question is that if the pipe is over the nominal thickness is PWHT is required?

Paragraph 331.1.3 state the governing thickness for PWHT is the component measured at the joint, but Table 331.1.1 refers to nominal thickness.

Which should I use to determine the PWHT requirement nominal pipe thickness or actual at the joint?

 

[weldstan]

If you have purchased 3/4" nominal thickness pipe and it is slightly over .750" wall at any location , it is 3/4" nominal pipe size and is not subject to PWHT. The latest Editions of B31.1 and B31.3, exempt carbon steel pipe from PWHT, regardless of thickness, provided a 200F minimum preheat/interpass temp is maintained when T > 1" and multiple layer welds are used.

 

[Shmulik]

Permissible variations in wall thickness acc. to SA-530 (general requirements) are 12.5% for under tolerance. Over tolerance depends on NPS (for 18" its 15%).
Table 330.1.1 clearly calls for Nominal Wall Thickness.
To my opinion, para. 331.1.3 only indicates the place to be referred in order to consider the thickness of the component that is to be welded. It not requires measuring the actual thickness at that place.

 

[sk10009]

PWHT needs are determined by the nominal thickness so the material should be PWHT.

 

[NDTHAND1992]

Weldstan - When referring to the latest code that is giving exception to the P1 over 3/4" rule. I only have access to a copy of 2013 are you refereeing to a addendum or the 2015 edition ? I have some 1.218 A333 24" welds that we would like to exempt if possible. I have reviewed my 2013 copy already and have not found anything. Thanks in advance for the help.

 

[weldstan]

B31.3 2014 Edition. Same is true for B31.1.

 

[NDTHAND1992]

Thanks bud

 

[XL83NL]

The 2014 edt is not effective until 6 months after the date of issue, which I believe was 27 feb 2015.

 

[NowshadKhan]

Please clarify my understanding, that per B31.3- 2014, PWHT is required for all thicknesses per table 331.1.1, while there is exemptions per Table 331.1.3 i.e. for P1 material having thickness greater than 1" PWHT is not required if preheated to 95 C (multiple layer welds t>5mm) and PWHT is required for all thickness lower than 1" for P1 materials.

 

[metengr]

No. PWHT exemption applies to all thicknesses for P-No.1 base material. The additional limitation imposed by Table 331.1.3 is preheat is necessary for base material greater than 1".

 

[NowshadKhan]

Dear metengr, it means PWHT is mandatory for thickness less than 1", however above 1" can be exempted due to preheat. What is the effective date of B31.3-2014 ? is there any code (ASME B31P) expected to cover the heat treatment requirement of B31.1 and B31.3?

 

[david339933]

NowshadKhan,

You are not grasping what is being said. PWHT is exempt for P1 materials of ALL THICKNESSES. If the nominal thickness is greater than 1" you must preheat to 200 Deg. F to avoid PWHT.

 

[NowshadKhan]

David

Thanks for the reply ..... if thickness is greater than 1" avoiding PWHT due to 95 C preheat is ok per table 331.1.3 as in my previous question but where is the reference that PWHT is exempt for P1 material for all thicknesses?

 

[DekDee]

Table 331.1.3

 

[sandypiping]

Thanks for all the infos. I came across the latest edition few days back and also noticed the changes. Am I correct in interpreting :
a. PWHT is exempted for P-1 materials for thickness up to 25mm?
b. For Pipe to pipe branch connections with R'Pad, the computed thickness as per clause 331.1.3 (referring Fig 328.5.4D) shall be more than 25mm in order to carry out PWHT (as per table 331.1.3)

 

[david339933]

A) Yes. However, if thickness is over 1" you don't have to PWHT. You must pre-heat to 200F prior to welding to be exempt from PWHT.
B) Yes. But again, if computed thickness is over 1" you don't have to PWHT. Pre-heat to 200F prior to welding and no PWHT necessary.

 

[david339933]

I am second guessing the response to B now. If computed thickness is >1" but nominals are <1" would you still have to pre-heat to 200F? I would say no, because the limitations refer to nominal thickness not control thickness.