PWHT for nonpressure parts to pressure parts - ASME Sec VIII Div I (2023)

[Vessel-SA]

Hi everyone,

I am trying to figure out whether PWHT (Post Weld Heat Treatment) is required per code for non-pressure parts welded to pressure parts under the following conditions:

The material is P1 Gr.1 for both the pressure part and non-pressure parts. PWHT is not required for service.

1) The thickness of the pressure part is 1.75". The non-pressure part (clip) is 1" thick. The fillet throat thickness is 0.75".

2) The thickness of the pressure part is 1.75". The non-pressure part (clip) is 1.625" thick. The fillet throat thickness is 0.5".

I am confused because UW-40(f)(5) states "the thickness of the weld at the point of attachment when a non-pressure part is welded to a pressure part" is the nominal thickness as used in table UCS-56-1. My understanding is that PWHT is not required for either (1) or (2) because the weld thickness is not greater than 1.5".
On the other hand, note (b)(3)(c) to table UCS-56-1 states PWHT is not mandatory "for fillet welds with a throat thickness of 1/2 in. (13 mm) or less used for attaching non-pressure parts to pressure parts. When the thickness of the pressure part exceeds 1 1/4 in. (32 mm), preheat to a minimum temperature of 200°F (95°C) shall be applied prior to welding each pass". This tells me the weld in example (1) requires PWHT but the weld in example 2 is exempt from PWHT.

Thanks!

 

[david339933]

Correct.

 

[Vessel-SA]

@david339933
What do you mean?!

 

[david339933]

What I mean is, scenario 1 requires PWHT and Scenario 2 does not, if pre-heated.

 

[Vessel-SA]

Thank you for your reply but what about the UW-40(f)(5)(-f) that states the nominal thickness is the thickness of the weld at the point of attachment when a non-pressure part is welded to a pressure part? The weld thickness in (1) is 0.75" and it is less than 1.5" which requires PWHT (if preheat) per table UCS-56-1 note (b)(2).

 

[Krausen]

Assuming minimum preheat, neither weld requires PWHT by code

 

[david339933]

Your second question made me actually open the Code.....you missed quoting an important part of the note in Table UCS-56. Note (b)(3) is exemptions to mandatory PWHT due to service (U-2)...and therefore not applicable to this scenario.

 

[Vessel-SA]

@ Krausen
the preaheat is required if the nominal thickness (weld thickness) is greater than 1.25", isn't it correct? so why would you think it is required?

 

[Vessel-SA]

@david339933
No, I didn't miss that part. I didn't post that part simply because those exemptions are applicable whether or not the PWHT is due to service or another part of the code. I base this off of an ASME interpretation below (question 3). Although the interpretation is too old, and I am not sure if it is applicable to the recent editions.
Standard Designation:

BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description:
Section VIII, Division 1, UCS-56
Date Issued: 04/11/1978
Record Number: BC-77-790
Interpretation Number : VIII-78-43

Question(s) and Reply(ies):

Question (1): Is it the intent of UCS-56(d)(6) and Note (2)(a) to Table UCS-56 that the exemption from postweld heat for material 1-1/2 in. and less, provided preheat over 1-1/4 in. is employed, applies to the thickness of the weld attaching a nonpressure part to a pressure part?

Reply (1): No. The reference to 1-1/2 in. as described in the above question applies to the thickness of the pressure part and not to the thickness of the weld. The provisions of UCS-56(d)(6) which refer to the thickness of the weld at the point of attachment when a nonpressure part is welded to a pressure part are applicable to the minimum time at normal temperature for nominal thickness if the weld requires postweld heat treatment.

Question (2): Which of the following statements regarding fillet weld size and exemption from postweld heat treatment where nonpressure parts are attached to pressure parts is correct?
(a) Fillet welds with a throat greater than 1/2 in. require postweld heat treatment when the thickness of the pressure part exceeds 1-1/4 in. and preheat is not used.
(b) Fillet welds with a throat less than 1/2 in. need not be postweld heat treated if preheat is used when the pressure part exceeds 1-1/4 in.
(c) Fillet welds with a throat less than 1/2 in. need not be postweld heat treated regardless of the thickness of the pressure part or the fact that preheat is not applied.

Reply (2): Items (a) and (b) are correct statements. Item (c) is incorrect.

Question (3): Do the exemptions in Notes (3)(a), (b), and (c) apply only if postweld heat treatment is required by UW-2?

Reply (3): No. The exemption in these Notes apply in any instance where a mandatory heat treatment was required.

 

[Vessel-SA]

@Krausen, david339933. could you tell me what you think of what I said?

I would appreciate it if anyone else could chime in too

 

[CuMo]

The PWHT requirements are typically defined by the materials and joints in/of the pressure envelope.
If your vessel does not require PWHT as per the Core rules - so your non pressure attachments wouldn't need it too.
If you're trying to determine whether you need PWHT based on the fillet weld sizes of your non-pressure attachment to your pressure envelope - I would say you're doing something wrong with the design.

By the way - your first weld combo isn't possible. 19.05 mm throat makes for 27 mm long fillet:
You can't allocate 27 mm fillet on a 25.4mm thick detail.

https://ibb.co/Jx6cnGX