Is PWHT of TTS weld joint necessary?

[ak1965]

Boiler tube leak is suspected in our plant.

Tubes are SA213 Gr.,T-11, 3.2 m thick and 38 mm OD (qty. 120 )

Tube sheet is SA387 Gr.11, 21 mm thick.


Boiler is high pressure.
Tube to Tube Sheet weld joint is strength weld.
We need to attedn thetube leak by plugging the leaky tube.

Is the PWHT mandatory after repair welding by ER80S-G on TTS joint? If yes, can it be avoided by using INCO82 filler wire.

FORUM SPEAK IS REQUESTED.

 

[metengr]

Based on the design of the weld and the materials of construction, no PWHT would be required, provided you use elevated preheat and keep the weld deposit thickness below 5/8" or 16mm. PWHT is provided for the base material, if required. The weld deposit composition is not a consideration in this case.

 

[Fizza453]

ASME Section I, PW-40.2 waives off the PWHT requirements for repairs on P.No.4 materials for the joints that have already received required PWHT. The exemption can be taken if all applicable conditions of PW-40.2 are met like preheat temp, depth of rework welding.

Hi Metengr,

Tube to tube sheet (i-e header) joints (P.No.4 to P.No.4) always require PWHT per Table PW-39. 16 mm weld deposit thickness exemption is only applicable to circumferential butt welds and this exemption cannot be applied to TTS joint. Please comment.



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Fizza453;
First off, this is a repair on an in-service component so ASME Section I construction rules do not apply, it applies for new construction only.

Second, if you decided to use Table PW-39-3 of Section I as a guide, I would argue that the tube is full penetration welded to the tubesheet surface and would be considered as a butt weld to the tubesheet. This is why I suggested an elevated preheat following the requirements in Table 39-3.

I could also recommend using a qualified temper bead procedure, which would require an elevated preheat and bead placement following the requirements of Part 3 in the NBIC.

Various ways to approach this as a repair, and not new construction.

 

[Fizza453]

Metengr,

Stub on joint, between tube to header, full penetration through the tube wall thickness is a butt welded joint, there is such an interpretation on Section IX for performance qualification, now I do not remember no of that interpretation. (that interpretation does not explicitly talk about TTS joint, it is about stub on nozzle joint with vessel wall)
Could you please mention, where it is written in the Code or somewhere in any interpretation that such a tube to header joint may be considered as a butt weld? It would be really helpful for us so that we may use Table PW-39-3 by considering it as a butt weld and then off course also we can use this concept of butt weld for Table PW-33.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[Fizza453]

Metengr,

In my opinion, above mentioned TTS should be considered as a butt joint only for the performance qualification and shall not be considered as a butt weld when applying the rules of PW-39-3, as QW-193 is not invoked by Section I, so welders would be qualified on butt welds in this case.

I further argue, you know in Addenda 2009, Section I changed its words from "circumferential butt welds" to "groove welds or combination of groove and fillet welds" in Table PW-39 for P-No-1 materials only. This change was made to include all long, circum, and all other groove welds.





Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Right, and this would be in my opinion a groove weld joining the tube to a tubesheet for repair and not new construction. Again, Fizza453, this is a repair on an in-service item and ASME BVPC I does not apply to in-service repairs. This repair would fall under the NBIC.

 

[Fizza453]

Metengr,
I agree Section I is not direct applicable in above case, however may be used as a guide book under NBIC NB23.

Apart from above discussion, please consider that we are talking about new construction under Section I, Tube to header joint as shown in Fig. PW-16.1 shall not be considered as a circumferential butt weld for the use of Table PW-39 (especially Table PW-39-3 for P.No.4 materials). Circumferential butt weld is defined in
PW-11.2 where it is clear that TTS joint shall not considered as a circumferential butt joint. PW-11.2 says these definitions apply for the use with Table PW-11 and "elsewhere in this Section".
So Table PW-39 falls under the word "elsewhere", so TTS joint is not a butt weld for the use of Table PW-39-3, hence T11 tubes welded to P11 headers shall also always be PWHT'd.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

As I mentioned I would use a temper bead weld repair.

 

[Fizza453]

Metengr,

I agree with what you all said above.

I am not talking about the repair or in-service work now.
Regarding new construction, my question and interpretation in my very last message is correct?


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

I would agree with your last message for new construction only.

 

[ak1965]

Boiler in our case is a waset heat boiiler & is designed as per ASME Sect. VIII and not ASME Sec.I...!

Discussion porgressing w.r.t. ASME Sec.I...!


Would any one like to change the opinion now & comment..!