Clad Steel Welding Process 7

[jsschweitzer]

I have a vessel made of A516 gr 70 clad with 316L Stainless Steel. The vessel is to be constructed in accordance with ASME section VIII and my question is related to the welding process of clad material. I do not have very much experience with this type of material. I need to find out if the carbon steel side or the stainless steel (clad) side should be welded first? Also, if any problems may be caused by the wrong side being welded first? Are there any documents from AWS, ASME, or other organizations that discuss which side of the plate should be welded first?

 

[GRoberts]

Proper techniquies can be used to weld either side first, but the techniques are different. Special Metals has some good detailed literature on welding clad steels.

 

[weldmete]

If the cladding is welded first and then the carbon steel weld joint is welded into the cladding cracking will almost cetainly occur.
Listed below is a recommended common technique for welding a cladded vessel:

1. Trim back the clad approximately 1/2" from the edge of weld joint.
2. Verify cladding is completely removed from the carbon steel so that the carbon steel weld doesn't get contaminated with Chromium, Nickel or Molybdenum. Note if the vessel wall is gouged into, weld build up the carbon steel wall thickness to meet code calculation requirements using an ASME section IX qualified WPS (weld procedure specification).
3. Weld the carbon steel portion of the weld joint with a WPS qualified to ASME section IX.
4. Grind the I.D. portion of carbon steel weld flush with the vessel wall.
5. Using an ASME section IX qualifed corrosion resistant weld overlay procedure weld the ovelay onto the stripped back area. Deposit the first layer using 309L or 309LMo filler metal. Deposit the second and possibly third weld layer using 316L.

 

[jsschweitzer]

The method of welding you described was described to me by another welding engineer, but I don't completely understand. One thing that I thought about was that if you weld the stainless side second, isn't it likely carbon content will end up contaminating the corrosion resistant layer of metal? Could you please explain to me why cracking will almost cetainly occur if the cladding is welded first and the carbon steel is welded second?

 

[stanweld]

The primary reason that you don't weld the carbon steel side second is that the initial carbon steel weld pass will dilute with the stainless steel and base metal carbon steel to form a martinsitic weld deposit - approximatel 5% Cr,2% Ni and > .10% C. This deposit is highly prone to cold cracking if preheat is inadequate.

 

[GRoberts]

There are some applications where the clad side of the material is not accessible after welding, so the carbon steel has to be welded second. To prevent the cracking Stanweld is talking about a nickel-based filler metal is used, such as ENiCrFe-2, after the cladding is first welded together from the backside. This also works when the clad side is not inaccessible, but is obviously going to be more costly in the filler metal department.

 

[jsschweitzer]

I am looking at the section VIII code book in section UCL-31 - Joints in Integral or Weld Metal Overlay Cladding and Applied Linings it states as follows:
"(b) When a shell, head, or other pressure part is welded to form a corner joint, as in Fig. UW-13.2, the weld shall be made between the base materials either by removing the clad material prior to welding the joint or by using weld procedures that will assure the base materials are fused. The corrosion resistance of the joint may be provided by using corrosion resistant and compatible weld filler material or may be restored by any other appropriate means."
This appears to cover corner joints, does this cover butt joints as well?

 

[sayee1]

Since this is just a discussion, I would like to add that there are consumables that is manufactured by Lincoln Netherlands called Kardo. One of the applications for this electrode is to weld a buffer layer on stainless steel weld/base metal in 2 layers on top of which filling up with standard CMn steel filler materials can be carried out. One of the recommendations is that stress relieving is a must after welding. This method is very dangerous and it is the welder who is responsible for the dilution with the stainless root runs. It is the dilution that MUST be restricted. It must be as low as possible, otherwise weld will have a martensitic microstructure. On the other hand this kind of welding is only economic in really very heavy wall thicknesses. So far as I know, there are only 2 or 3 companies in the world who has the experience. So technically speaking it is possible to deposit C steel on top of SS without cracking if you can really restrict the C % of the buffer layer and use almost pure Iron deposit.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[stanweld]

UCL-31 (b) is not mandatory for other joints. UCL-31 (a) "...welding procedure used shall be such as to minimize the formation of brittle weld composition..." does.

Essentially ASME VIII, Div. 1 weld designs mandate weld strength equal to or greater than that of the base metal used in the design and will meet minimum ductility requirements of ASME IX as demonstrated in the welding procedure qualification. Depending on the service environment and weld accessibility there are a number of approaches to making these joints - most common are either similar to that proposed by weldmete or GRoberts.

 

[priyasachin]

dear friend,
welding clad material is a standard practice now. you can weld from any side. if it is a single side weld welding first the CLADSIDE IS INEVITABLE. When so is the case seal the gap with TIG with the clad quality weld metal build it up by this or any other method till the 3mm layer is filled,put in a layer of richer alloy or nickel metal layer and weld the carbon side with the required electrode and method you have choosen.
when both the surfaces are accessable, follow the method suggested by some one earlier, cut back on the clad layer on either side of the weld, and if it is a double 'v' joint fill the 'v' till the clad surface, grind it clean deposite a rich layer of CRL and complete the weld of clad material.
turn to the other side and complete the weld after back gouging the root and grinding.
the richer layer I am talking is the one which has higher percentage of major alloying elements than the clad layer. for ex. if the clad layer is ss304, use either ss 309 or 310 as intermediate layer. if the clad layer is ssxxx-L alloy the carbon migration has to be contended with, hence a nickel layer is desirable as intermediate layer.
welding without the intermediate layer between carbon steel side and the CRA lyer will render the mixed material poor in all properties including the corrosion resistance.
hope the matter is clear.
regards,
MRCN

 

[CalvinKelly]

I would suggest that the root pass on the clad side be a high nickel alloy, either ENiCrFe-3 as previously suggested, or high Ni-Mo alloys such as ENiCrMo-4 (C-276), ENiCrMo-10 (C-22) or ENiCrMo-14 (686 CPT). The high nickel will minimize or eliminate concerns about martensite on the carbon steel side, an the Mo will ensure that the clad side, whatever the dilution into the 316L weld cover pass, has sufficient corrosion resistance. The best procedures for welding clad plate are those published by the alloy producers Haynes International, Kokomo, Indiana and Special Metals (formerly Inco, formerly Huntington Alloys Div), Huntington, West Virginia. Committee written procedures tend to be less directly useful.

James Kelly

http://www.rolledalloys.com

 

[jsschweitzer]

The information contained in articles published by the organizations below support the two primary methods of welding clad steel as follows:

1. Remove cladding during joint preparation, then weld the backing steel (base metal) with the appropriate carbon or low-alloy steel consumable, and finally, the region where the clad was removed during joint preparation will be overlaid with the appropriate high alloy consumable

2. Weld the entire thickness of the clad plate with the appropriate full alloy consumable

Published Information Sources:

International Steel Group (formerly Bethlehem Steel) - page 7 (9 in pdf)

http://www.bethsteel.com/customers/pdfs/clad.pdf

Nickel Development Institute (NiDI), the American Iron and Steel Institute (AISI), the American Society of Metals International (ASM Int’l), and the Committee of Stainless Steel Producers - page 33…36

http://www.nidi.org/multimedia/tech...terature_pdfs/9000_aisi_publications/9002.PDF

Special Metals (formerly Inco Internetational) - page 23

http://www.specialmetals.com/publication/tech_bulletin_welding.pdf