P6 to P6 Procedure, Including CA6NM without PWHT

[DonRoss]

In lieu of developing some P6 procedures using Low Carbon E(R)410NiMo fillers, my employer has tasked to develop a WPS for welding P6 to P6 without PWHT.

As permitted by ASME UHA-32, under P6 Gr 1, 2, 3 materials; PWHT is not required for pressure retaining components made from 410 SS materials for SA-182 Grade F6a, SA-240, SA-268 and SA-479 with carbon content not exceeding 0.08%, provided the plate thickness at the welded joint does not exceed 3/8”, and for joint thicknesses greater than 3/8” to 1-1/2” provided a preheat of 450°F is maintained during welding and that the joints are fully radiographed.

For filler, I selected Inconel 625 because of its desirable mechanical properties for low & high temps, as well as for its ability to handle corrosive conditions. The issue I’m having, is that, none of our suppliers carry or are able to source S41000 material with a carbon content of 0.08% max, as directed by ASME. I am questioning this, as this limitation is rather difficult to comply with. ASME SA-240 S41000 specifies a Minimum carbon content of 0.08% and a Max of 0.15%.

The only other option to use is CA6NM Material (S41500) [P6 Gr 4] as a substitute; however, doing this is not a very good representation of what is really going to be fabricated.

Relative to this, I am also looking to develop a Weld Repair procedure to weld CA6NM casting without PWHT. As permitted by ASME, Table UHT-56 for SA-487 CA6NM, it specifies Nominal Thickness requiring PWHT is over 0.58 in. Thicknesses beyond this with even using Inconel 625 still would require PWHT, respectively. My thoughts in getting around this would be to develop a temper bead procedure according to ASME IX QW-290, using 1-1/2” thk CA6NM material. The minimum weld layers of weld metal required is two, the root or initial weld pass on the base material, and the second, to temper the root or initial pass. These two layers shall comply with the essential variables for temper bead welding qualification, QW-290.4. Subsequent passes thereafter, will not require tempering since Inconel is considered exempt from this process.

Has anyone developed procedures as such, or similar?
Your comments and or suggestions are appreciated.

Thanks,

Don

 

[metengr]

If this is for new code construction, you will not be able to use temper bead for the CA6NM. The lower carbon 410 stainless came through as a code case for a boiler manufacturer in Europe.

I had developed a temper bead weld procedure for CA6NM using an austenitic filler metal that was not part of any construction code or NBIC requirements. It was for weld repair of a pump case.

 

[DonRoss]

Hi metengr,

Thanks for your input. This would be for repairing Pump casings built in accordance to API 610, in the event of a failed hydro or from cracking in service.

Welding procedures and PWHT would have to be in accordance with ASME VIII and IX.

If you don’t mind my asking, why would CA6NM be exempt from being able to use Temper Bead Welding for In-Process Repair?
ASME Section VIII & IX, QW-290 do not specify material restrictions; unless I've missed something...

Developing a procedure outside of ASME would have the customer hard pressed about it.

 

[DonRoss]

I found this thread from a while back with some similar discussions.

http://www.eng-tips.com/viewthread.cfm?qid=304849

 

[metengr]

If you don’t mind my asking, why would CA6NM be exempt from being able to use Temper Bead Welding for In-Process Repair?
ASME Section VIII & IX, QW-290 do not specify material restrictions; unless I've missed something...

The way I read your post, and citing ASME Section VIII, Div 1 it sounded like you were repairing a pressure retaining item, which would be NBIC or API 510 code space. Temper bead is only recognized for certain P-No base materials, for which CA6NM is not one of them. So, as long as you are outside of these in-service repair standards, you can use sound engineering judgment to perform weld repairs.

 

[DonRoss]

Thanks for the clarification. Unfortunately, by default, our position is that, an API 610 Pump Case is considered a pressure retaining component and that all welding and fabrication shall be in accordance with ASME VIII Div 1 & IX, not unless exception by the customer has been taken or otherwise specified for construction outside of ASME.

 

[stanweld]

The pump case is outside the scope of ASME VIII per U-1 (c)(2).

 

[DonRoss]

Correct; however, according to API 610 11th Edition per 6.12.2 – Castings, 6.12.3 - Welding and 6.12.4 – Low Temperature Service, provides the option by the purchaser to otherwise enforce ASME VIII Div 1 & IX as part of their specification or as the construction code. Usually, as a minimum the customer will default to ASME VIII Div 1 as the construction code IF no additional specs are provided.

 

[stanweld]

API 610 does not require design and construction per ASME VIII. It does require that welding procedures be qualified per ASME IX or equivalent EU requirements. It does require impact testing per ASME VIII. It does require specific NDE per ASME VIII. It is up to the Manufacturer or the Purchaser whether to follow all requirements of ASME VIII regarding design/construction.

 

[DonRoss]

Right, so in this case, developing a CA6NM Weld Repair Procedure without PWHT in accordance with Section IX is permissible; however, it shall be provided as an option to the end-user for their review & approval, outside ASME Section VIII. Impact and NDE requirements shall apply as required.

Thanks for clarifying.

 

[stanweld]

DonRoss,
You must design the pump casing for the 20 yr life defined in API 610. Be sure that your WPS without PWHT will be suitable in meeting the criteria; it may not be the case for all service applications.

 

[DonRoss]

Excellent point! You're absolutely right, this is subject matter that will be discussed with my employer.

Thanks again,

 

[DonRoss]

Gents,

If you will, going back to this thread I posted about PWHT Time @ Temp for P6 Gr 1 [S41000] to P6 Gr 4 [CA6NM Class B]:

http://www.eng-tips.com/viewthread.cfm?qid=347882,

and the complexity surrounding trying to achieve Hardness results to meet NACE using PWHT requirements according to ASME VIII Div 1.

It’s been clarified that API 610 does not require design and construction of Pump Casings to be in accordance with ASME VIII Div 1, if otherwise specified by the customer; Welding procedures, Impact and NDE requirements, however, are required to commply. Shall the PWHT temps specified for these materials follow ASME VIII Div 1 as well, given that, impacts are required?

My thoughts are *yes*

To recap:

ASME PWHT Temperature Requirements:
- According to ASME VIII Div 1, Table UHA-32, P6 Gr 1 specifies Normal Holding Temp of 1400°F min up to 2” for 1.25 hr, Over 2” to 8” for 2.25 hr for each additional inch over 2”.
- According to ASME VIII Div 1, Table UHT-56, P6 Gr 4 (SA-487 CA6NM) specifies Normal Holding Temps of 1050°F – 1150°F for 1.25 hr Min. for Nominal thickness >0.58”.
- According to SA-487, CA6NM Class B requires two PWHT cycles to meet NACE hardness of 255 BHN, 1st Temper of 1250°F +/-25°F and 2nd Temper of 1150°F +0°F/-25°F as FINAL.
- Heat up rates are according to UCS-56(d)-(1)(2)
- Cool Down Rates, according to UHT-56(c), UCS-56(d)-(5) need not apply.

PWHT Requirements specified on the WPS are a combination of the two to meet both material requirements.
- 1st Temper at 1425°F +/-25°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.
- 2nd Temper at 1150°F +0°F/-50°F for 1.25 hrs per inch for thicknesses less than 2”, 2.25 hrs per additional inch thickness.

PWHT Requirements specified on the PQR are a combination of the two to meet both material requirements.
- 1st Temper at 1425°F +/-25°F for 13 hours
- Air Cool to below 77°F before 2nd Temper
- 2nd Temper [FINAL] at 1150°F +0°F/-50°F
- Air cool to ambient

 

[DekDee]

Guys,
Please excuse me if this question seems naive.
Why would a pump casing have anything to do with ASME VIII - it is not a pressure vessel or a pressure retaining component ?
Would not the pump casing be subject to the applicable piping code of the product flowing into and out of the pump casing ?
Cheers,
DD

 

[DonRoss]

DD,

If you reference API 610, 11th Edition, Sections 6.12.2 & 6.12.3.1, applicable code requirements are ASME VIII Div 1 and IX.
The requirements are either specified by the customer or it is a decision made by the manufacturer.

 

[DekDee]

Don,
The reason for my confusion was I was involved in a project in Australia in 2003 at a Shale Oil R&D project built by Bechtel.
We needed to weld some 316 nipples on to the side of the CA6NM pump casings (for some sort of injection to dilute the product)and I was instructed all welding procedures were to comply with ASME IX / B 31.3.
Regards,
DD

 

[DonRoss]

Correct, we as well have done the same thing by customer specification.