Welding Duplex Stainless Steel

[Heyner]

Hi everybody:

I'm about to start construction of a Duplex stainless steel (UNS S31803) vessel, According to Section VIII div 1 and stamped.(ID=84" TTL=180")

Have you experience welding this kind of steel? which is the more recommended process? (FCAW, GTAW, SMAW, SAW, Other). Thickness is 12mm (0.472").

If someone can help me too in finding good references regarding welding quantities calculation... would be great.

You know, this welding material is so expensive, about USD 30 per pound!!

Thanks a lot!!

 

[JoeTank]

In my prior life, I always wrote several project specs that was heavily tilted towards contractors that already had experience with duplex. Thirty bucks a pound for electrodes will seem pretty cheap compared to the misery you and your client will have if you don't get this done right the first time. I commend you for seeking the input of a forum like this, but what you really need is a welding expert. I could recommend a couple for you (No, they do not work for this company) if you will send me an email as noted below.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JoeTank]

Sorry, I forgot to email in previuos post. braune@tankindustry.com

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[roca]

Heyner
Some notes for you - hope it helps
DUPLEX SS REQUIREMENTS

PQR specimens shall be toughness tested, hardness tested, and examined microstructurally. Microstructure of the weld and the HAZ shall contain between 30 and 70% ferrite. Toughness tests shall be run on the weld and HAZ, and meet an average of 20 ft-lbs over three tests with no individual sample less than 15 ft-lbs at -20?F (27.20/20.3 J at 30?C). Hardness limits shall be agreed upon before testing.

All root passes shall be made with GTAW. Root pass must be back purged.

Shops must be qualified by CLIENT to weld duplex SS.

Only GTAW, GMAW, SMAW, and SAW are Clientepted for welding duplex SS.

Heat input shall be limited to 20-63 kJ/in (0.8-2.5 kJ/mm). Interpass temperature shall be limited to 300?F (150?C) for 22% chromium duplex SS, and 250?F (120?C) for 25% chromium duplex SS.

Only neutral shielding gases are allowed. Active gases (with N2, O2, or H2 additions) are only allowed with prior written consent of CLIENT.

Production welds shall be hardness tested at the same frequency as the radiography.

Cosmetic remelting and downhill progression are prohibited.

Post weld heat treatment (pwht) is not normally needed for duplex SS. All PWHT procedures shall be approved in advance by CLIENT.

Flame cutting and flame straightening are prohibited

 

[roca]

Heyner
Here's also an ammendment to the heat input data

Heat input shall be limited as follows:
- For 22% chromium duplex SS:0.5 to 2.5 kJ/mm
- For 25% chromium duplex SS:0.5 to 1.5 kJ/mm
Interpass temperatures shall be limited as follows:
- For 22% chromium duplex SS: 300?F (150?C)
- For 25% chromium duplex SS: 250?F (120?C)

 

[metengr]

I would agree that you should seek welding expertise with fabrication of duplex ss. The following web sites contain good, general technical information to prepare yourself for asking the right questions;

http://www.gowelding.com/met/duplex.html

http://www.outokumpu.com/applications/documents/start.asp

The second web site (Outokumpu) has several technical articles regarding welding of duplex stainless steels with recommended filler metal and welding parameters that would supplement the responses above.

 

[tickle]

The fabrication of the vessel should also be followed by passivation of the heat effected zone at least. There are different ways of passivating the duplex.

For a duplex vessel the filler metal should be super duplex because super duplex degrades to duplex (ferrite to austenitic not sure exactly what).

Try the australian stainless steel association -

http://www.assda.asn.au

 

[Heyner]

Thank you all for the help, it is really good!

 

[Heyner]

Roca:

It seems what you said is a portion of a specification? ("Clientepted" appeared when replacing ACC by CLIENT?)
May be not all of them are mandatory requirements, right? but, anyway, is a good info, thks.

 

[roca]

Heyner
You're in the wrong job - you should be a detective - yes its taken from a spec.

 

[GRoberts]

For UNS S31803, 2209 welding consumables are the norm. I don't know where you are located, but the prices you are getting seem way out of line. We normally use SMAW and FCAW where I work for 22 Cr duplex, and for SMAW, we get electrode for $6.20-$10/lb and flux cored electrodes for $6.30/lb.

 

[dig1]

One other point, I would specify that the material be dual certified UNS S31803/UNS S32205. This way you get the upper end of the nitrogen range (0,14-0,20) which is better for the welding. It also keeps you in the upper range of the chrome and moly, which you may or may not need for the process.

The latest pricing I've seen on 2209 FCAW is about USD20/pound

Here is a link to the Nickle Design Institute, free download for "Practical Guidelines" on 2205

http://www.nickelinstitute.org/mult...iterature_pdfs/other/39309_IMOA_Duplex_ii.pdf

TAPPI (Tech Applications Pulp & Paper Industry) has a TIP which is very good on 2205 as well.

I would suggest purchase a Fisher Ferritescope, or similar device. I just came from a project where someone grabbed 309 and used it in a seam. It showed up immediately because the ferrite was so low. Due to the configuration, a run-off tab would not have been taken there and it would have been missed during fabrication.

Be careful with your heat on FCAW because we have had situations where microslag was introduced and the qualification coupon nearly failed the ASTM A923 Method C test (weight loss test for determining presence of detrimental intermetalic phases). Heat input was adjusted and results of the new coupons were dramatically improved

It is common to specify ASTM A923 Methods A, B, & C (do not use A to eliminate B & C testing).

Are your heads cold formed or hot formed. I would guess cold from the geometry and thickness you gave. In this case, I would recommend PT inside and out. This helps identify areas (small surface cracks) that were caused during forming and not as the results operation (process).

Please know that 2205 is not immune to SCC and there are examples of it occuring. This is why it is best to eliminate as many as of the forming cracks as possible so an inspector doesn't find something that isn't there and want a sample cut out for examination. Painful and expensive lessons.

If you need some EXCELLENT 2205 shops you can post your e-mail address and I'll send you some references and their web pages. I have no financial ties to any of them and they have done great work for this size equipment in the past.

 

[Heyner]

Thanks a lot!!!

you can send me further info to:

heyner_garcia@hotmail.com

thanks in advance, again...

 

[Heyner]

Dig1:

What does SCC mean?

 

[dig1]

stress corrosion cracking

 

[metengr]

I just noticed that for UNS 32750 there was an ASME Code case for using this duplex stainless (Code case 2047).

 

[EdStainless]

316 is not suitable for any seawater service. Not if you want it to last more than months anyway.
245 is a superaustenitic, there are about half a dozen of this type of 6% Mo alloys on the market. Good strength, easy to work with and good corrosion resistance in seawater.
The superduplex are a different animal. There are only a few on the market, and they are tricky to work with. But if you really need high strength and seawater service they can do the job.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm