PWHT Requirements - Section VIII Div 1 U-stamped vessel 2

[Blizzardo]

I have a question related to a Section VIII Div 1 U-stamped vessel. The vessel is manufactured of SA516 Grade 70 (P1) - 2.5" wall thickness, running at 150 PSI and 350F. We need to add-in a number of nozzles to the vessel. The nozzles are SA789 (P10H) and SA240 (P10H) respectively. Where the nozzles are to be cut in, it is expected that the welding work is to be completed with 309L stainless filler metal. In consideration of both ASME Section VIII and NBIC Section 3, is Post Weld Heat Treatment (PWHT) of the nozzle locations an absolute, or can this be eliminated?

Further to the above, there are some attachments on the interior of the vessel (SA240 - average thickness 1/2" - 3/4") that will require welding to the interior of the vessel (fillet welds). The filler metal is expected to be 309L stainless. Would PWHT be an absolute requirement at the weld locations (P1 to P8)?

Any assistance is greatly appreciated.

 

[pradipgoswami]

A question: Why this vessel is made of such awkward materials combination :SA 516/70 shell, 300 series austenitc S.S internals, Duplex 2205 Nozzles? Not sure what're the process conditions are. A change to Clad construction(shell-SA 516/70 clad with 300 series or with duplex 2205) could have avoided many of the fabrication problems, as what you're facing now.

Coming back to your query:
Duplex nozzles should never be exposed to PWHT temperature of C.S(600-620 DegC).It will simply embrittle the BM and the welds also. A good solution to this problem should be(Ref API-RP-582, Table-A3):
-Butter the nozzle cut-outs/WEP with E309LMo
-Perform PWHT
-Weld Duplex nozzles at the end.

Same logic should apply for welding of internals. The locations should be buttered with E-309L or 309LMo(if internals are 316 or Duplex 2205.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[metengr]

This is obviously an inservice vessel with nozzles being added. This can either be a repair or alteration depending on type of nozzles being added following the requirements in Part 3 of the NBIC. PWHT should be based on Section VIII, Div 1 requirements or if impractical use of an alternative welding method in Part 3 of the NBIC. You should review Welding Method 5 in Part 3 of the NBIC as an option or butter the weld preps on the vessel using 309LMo, PWHT locally, and complete the weld joint using 309LMo.

 

[Blizzardo]

All,

Thank you for the expedient response. I did consider the buttering pass in 309L on the P1 material as this was a recommendation we used in another P1 to P8 procedure for piping. My main concern here is the impact of PWHT of the completed weld on the nozzles being the dissimilar metals and time and expense with performing PWHT on the 2.5" P1 material. The buttering pass PWHT I believe we can cover, however PWHT of the entirety of the 2.5" weld after the fill with 309L is of concern.

Metengr - I'll investigate your NBIC reference more thoroughly.

Pradip - In your response, are you suggesting PWHT of the entirety of the weld, or just the buttering pass?

 

[weldstan]

Under UCS-56, the thickness of the weld to the P1 pressure material dictates the requirements for PWHT, assuming PWHT is not for corrosion service. Can the nozzles be set on instead set in with the weld thickness less than 1.5 inches?

 

[Blizzardo]

The vessel is a Digester in the pulp and paper industry. Filled with chemicals, wood chips and water to facilitate the breakdown of lignin in the wood chips. The nozzles are to be installed through the entirety of the vessel wall. A sch. 80 pipe with a weld neck flange. The vessel wall is to be cut for the nozzle (6"), then beveled (both sides) around the hole to 30-degrees. The weld detail notes 309L filled on both the inside and outside of the vessel wall. This is my reason for concern on the PWHT of the entire weld as the weld is essentially P8 material and I'm concerned that PWHT will have an adverse effect on the weld.

 

[pradipgoswami]

Blizzardo,

What would the materials of construction for the nozzles, Duplex S.S or Austenitic S.S? According to original posting " The nozzles are SA789 (P10H) and SA240 (P10H) respectively".

PWHT(SR) is never recommended for Duplex Stainless Steel. Duplex simply embrittles, when exposed to 600-620 Deg C zone for PWHT as, it forms of intermetallic compounds. If Duplex is used for nozzles , nozzle bevel should be buttered with 309LMo and PWHT-ed before insertion and welding(of nozzles). 6"OD nozzles would typically require Set-Through(Set-In) type of nozzles. Smaller dia(4") and below could be set-on type.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[Blizzardo]

Pradip,

Thank you for your response.

There are two separate types of nozzles.

The first is ASME SA240 Grade S32205 (P10H). This nozzle is an inset 2.5" thick, 10" diameter machined plate (same thickness as the vessel wall) that's welded flush to the wall of the vessel after cutting the 10" hole and beveling the vessel wall. The plate is 10" around with a 3" hole in the centre with machined and threaded holes for securing inspection devices to the nozzle.

The second nozzle is a piece of 6" sch. 80 pipe, ASME SA 789 Grade S32205 (P10H), with a 6" weld neck flange on one end. This nozzle equally goes through the vessel wall after cutting a 6" hole. The vessel wall is also beveled on both sides, the same as the 10" nozzle prior to welding.

For both nozzles, there is a significant amount of 309L filler metal to be deposited to fill in the 30-degree included angle that's indicated on the weld detail on both the inside and outside of the vessel. It's this stainless material (the weld metal) that's of concern.

Of course I appreciate any insight on this alteration. Thank you.

 

[metengr]

Then use 309L, which is formulated for exposure to PWHT because it is used for dissimilar metal welds between duplex and CS. What you do not want is sigma phase formation upon exposure to PWHT with having Mo in the filler metal. After buttering, locally PWHT for the benefit of the carbon steel base material, and complete the weld joint using 309L filler metal or 2209 with no PWHT.

 

[Blizzardo]

Metengr,

Thank you for the additional assistance. Can you please advise as to where I could find some supportive literature defining your recommendation? I ask as this may come up with the Client who will very likely have their own group of opinioned personnel who may hold an alternate viewpoint on the matter.

On the matter of PWHT of the buttering pass, can you please advise as to the temperature and duration you think would be necessary considering the materials I have indicated.

Thank you.

 

[metengr]

Blizzardo;
Well, for starters here is an excellent paper on DMW's and selection of filler metals.

https://nickelinstitute.org/~/Media...idelinesforWeldingDissimilarMetals_14018_.pdf

With that said, you will need to qualify a WPS/PQR for a groove weld using the suggested approach below - 1. butter the surface of the weld prep on the existing CS vessel using a 1/4" thick layer of 309L with a 200 deg F preheat.
2. Once this step is completed, perform local PWHT at 1100-1150 deg F for 30 minutes at temperature.
3. After PWHT, perform surface NDT of the 309L butter layer, and if acceptable, complete the groove weld using either 309L or 2205 filler metal with a 200 deg F preheat, and 350 deg F maximum interpass temperature with no PWHT.

If your client has concerns with exposure of the 309L to PWHT for the carbon steel, which is done routinely for thick CS vessels, perform corrosion testing of the 309L to evaluate the effect of PWHT and as-welded.

 

[Blizzardo]

Metengr,

Thank you again for the additional information and the reference article. I will review the recommendation with my welding engineer today as we expect to be qualifying the procedure for the work in the next few days.

A couple of additional comments/questions.

It is presumed that the buttering pass would be required over the entirety of the carbon steel (P1) area that is beveled. We will butter to 1/4" thickness as you have noted. I have indicated this on the WPS.

Similar to my question that initiated this thread, we will also be installing some supports and screens in the vessel that are SA240 (P8). These installations will require fillet welding to the interior of the vessel. Would the fillet weld equally require a buttering pass of 1/4" thickness and PWHT as you have indicated at all areas wherein there is a dissimilar weld? We would use 309L again as the filler metal.

 

[metengr]

The welded attachments may not be subject to PWHT because of weld deposit thickness. Check UCS-56 and exemptions for attachment welds.

 

[Blizzardo]

Metengr,

Thank you for the reference (again). You're a wealth of knowledge and I certainly appreciate your assistance.

Under Table UCS-56-1 the GENERAL NOTES indicate the following;

(3) for welded joints of all thicknesses if required by UW-2, except post weld heat treatment is not mandatory under the conditions specified below;

(c) for groove welds not over 1/2 in. (13mm) in size or fillet welds with a throat thickness of 1/2 in. (13mm) or less used for attaching nonpressure parts to pressure parts provided preheat to a minimum temperature of 200F (95C) is applied when the thickness of the pressure part exceeds 1 1/4 in. (32mm).

So...to my query, as long as I maintain preheat of 200F (95C) and my throat thickness of the fillet weld for attaching the nonpressure part does not exceed 1/2 in. (13mm), then PWHT is not required.

 

[metengr]

Correct.

 

[pradipgoswami]

Another piece of advice would be to perform UT on the proposed areas of nozzle cutouts. Areas containing any material defects(e.g. laminations) should be avoided. As a function of composition, 309L/309LMo may show reduced ductility after PWHT. Advice is to use welding consumables from the reputed manufacturers with appropriate MTR.

As the welding is significant, steep grooves, with 30" included angle may generate hot cracking. Hence wider groove angle 45"(at least) could be beneficial. Distortion of welds could be minimized with evenly welded supports.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[Blizzardo]

Thank you Metengr and Pradip.

On the included angle, my Welding Engineer also suggested increasing the angle. The drawings provided by the manufacturer list 30-degrees, so I'll have to go back to them to ask if the angle can be increased.

Regarding the PWHT of the butter pass and the impact to the corrosion resistant properties of the 309L, I thought to overlay the 309L slightly past the PWHT section of the P1 material to cover the affected zone of the buttering. If I limit the overlay to less than 1/2", then the thought was that additional PWHT would not be required in this area and we maintain the corrosion resistance we're looking for.

A diagram attached to illustrate.