Section VIII PWHT after Weld Repair

[newweldeng09]

Situation: I have a P1 case that has P1 nozzles welded to it that has been post weld heat treated in a furnace charge. It was finished machined and has been sent to hydro. test. During testing, a leak was discovered due to a mis-machined area on an internal feature of the case, which is not connected to the nozzle to case welds. A base metal weld repair needs to be performed. Less than 1/16" of weld metal is going to remain after final machining to repair this area. Per UCS-56(a), (2nd Par.), all welds in pressure vessels shall be given a PWHT at a min. temperature in Tables UCS-56 and UCS-56.1 when the nominal thickness exceeds the limits in those tables. In this case, nominal thickness, as defined in UW-40(f) is the depth of the repair, which is well under the 1.5" of Note 2(a) and the 1.25" of Note 2(b) in Table UCS-56. Therefore, PWHT does not need to be performed. However, in UCS-56(e), vessels that have been PWHT in accordance with the requirements of this paragraph shall again be PWHT after welded repairs have been made.

Is PWHT to be performed following this repair because the case has been PWHT previously or does UCS-56(e) apply only to weld repair areas on the nozzle and case close to the weld and on the weld itself?

 

[metengr]

No. Please review below;

(e) Except as permitted in (f) below, vessels or parts of
vessels that have been postweld heat treated in accordance
with the requirements of this paragraph shall again be
postweld heat treated after welded repairs have been made.
(f) Weld repairs to P-No. 1 Group Nos. 1, 2, and 3
materials and to P-No. 3 Group Nos. 1, 2, and 3 materials
and to the weld metals used to join these materials may
be made after the final PWHT but prior to the final hydrostatic
test, without additional PWHT, provided that PWHT
is not required as a service requirement in accordance with
UW-2(a), except for the exemptions in Table UCS-56, or
as a service requirement in accordance with UCS-68. The
welded repairs shall meet the requirements of (1) through
(6) below. These requirements do not apply when the
welded repairs are minor restorations of the material surface,
such as those required after removal of construction
fixtures, and provided that the surface is not exposed to
the vessel contents.

 

[newweldeng09]

Based on your response and reading Section VIII, PWHT is required to be performed because the case was previously PWHT. The original PWHT was 1150F for 8 hours. Subjecting the finished machined case to this temperature and holding time will distort some internal dimensions. A localized PWHT is not acceptable in this case because it will distort the areas that need to be weld repaired. Also, temper bead welding of P1 material is not mentioned in Section VIII as an acceptable means of PWHT. Can you offer any suggestions to effectively PWHT without distortion?

 

[metengr]

Are you sure you have not met the requirements in (f) above? I did not have time to review it and figured you could do this and determine on your own. If you need to PWHT, I would use the local PWHT in Section VIII, Div 1 which uses a local circumferential band. Search for it and decide if this will be acceptable.