FCAW process in pressure vessel manufacturing

By jon20013 (*****)

Date 03-30-2007 11:55

FCAW is no problem in pressure vessel industry in the USA, in fact it's very common. The only concern may be for carbon steel vessels where impacts might be required. In the most general terms, this applies to vessels in excess of about 16mm in thickness. Of course there are a multitude of other reasons impacts may appliy but that's a good "general" rule.

By js55

Date 03-30-2007 14:07

Jon said it right. FCAW is common in pressure vessels. Tons of it is welded on them every day. And traditionally impacts have been an issue for wires because you can only fit so much stuff inside those little wires. By the time they get done with shielding gas generators, wetting agents, fast freeze agents, deoxidizers, etc., there ain't much room left. But the standard 20/20 (20ft/lbs/-20degF) test has become routine for CS wires to achieve and some wires do far better.
Even low ally wires, say, of the CrMo variety are much improved in impacts, even though they are intended predominantly for high temp applications where toughness is generally not considered an issue (there are concerns for cyclic/start up/ambient/cold weather shipping toughness).

By George-kh (**)

Date 04-01-2007 20:42 Edited 04-01-2007 20:52

Rutile wires with fast-freezing, stiff slags (E71T-1 types) are available for all-positional welding, where-as downhand versions (E70T-1types) use more fluid slag for high travel speeds. In both cases, slags are easily detached. Ni alloying with Ti, B-micro alloying provides good low-temperature toughness down to -50 C degree and CTOD properties (E81T1-Ni1 types); but only in the as-welded condition. Higher required strength levels become increasingly difficult to match with sufficient weld metal toughness and cold-cracking resistance. The rutile formulation is also less suitable for creep-resistant types, because stress relieving reduces weld metal toughness. In both cases, basic cored wires offer a better basis.
However, risk of lack of fusion on thick base metals is high with basic type cored wires, because of short-circuiting metal transferring, which occur with basic type cored wires. I know ESAB has developed some basic type cored wires with spray arc metal transfer mode, which has solved this problem but I can not remember their trade names. Contact ESAB for more detail.

By jiweiming (**)

Date 04-02-2007 02:33

thanks,Jon,Js and George.
I mean whether FCAW process can be used in main weld seam of pressure vessels, not only be used in nonpressure parts welded to pressure parts. If it can be used, what the specification for the FCAW wire is, such as content of hydrogen diffusion, strength,etc. At present, what types of materials can be welded in the manufacturing of pressure vessels except carbon steel, stainless steel. Can it be low temperature steel, heat-resistance steel,etc? If it is SA516 Gr.70 or 60, which wire should i choose?
Many thanks.

By js55

Date 04-02-2007 13:43

The overall answer is that there is nothing inherently restrictive when it comes to using FCAW for pressure vessel applications.
And as far as low temp steels, high temp steels, in my opinion actually misnomers(SA-333 Gr6 for example is used every day on non cold temp applications because of its automatic impact testing) and, I think you are making it too complicated. The 70T-1's and 71T-1's are used by the ton every day for low temp/high temp either one.
You have to take a look at what your actual service regime will be. Does the temperature go beyond the ability of the carbon steel wire to accomodate. Generally in high temp the BM will be speced as CrMo for example. But if the BM is carbon in a low temp it is entirely possible that a standard CS wire can be used. Keep in mind, once the heat of welding is imposed upon a fine grained steel the fine grain is essentially gone for a certain portion of the HAZ. With fine grained steels you sure won't make the HAZ better.
FCAW wire manufacturers do offer wires that achieve better impacts than others they offer and it is worth taking look at. Establish a testing regime based upon your spec, consult your vendor and test your wire.

By jiweiming (**)

Date 04-04-2007 01:14

Thanks,js.
If I shall have a pressure vessel whose material is 1.25Cr-0.5Mo or 2.25Cr-1Mo,or SA203 Gr.D OR E to produce, and FCAW process is to be used in main meld seam such as A seam or B seam, what wire should i chose? If the vessel needs to be PWHT or not. what i have to pay attention to then? Your answer will be appreciated.

By js55

Date 04-04-2007 14:29

B2 and B3 will be the choice for the 1 1/4 and 2 1/4 Cr respectively. These materials are very common in the power industry and they hold up well under PWHT. A vessel will most likely need to be PWHT. There may be some exemptions for thinner materials but as the alloy content is increased the exemptions become more and more restricitive until they disappear. Consult ASME VIII for minimum requirements. They will be very material specific.

As for nickel steels I am assuming you have a low temp application. C Series suffixes are what you are looking for if you intend on using nickel steel fillers. Pay attention to Charpy impact requirements. Someone else may know but I'm not sure there are FCAW's available for nickel steels for services at -150F. If FCAW is your choice however I would suggest Nickel based alloy fillers (perhaps NiCrFe's). They will match the thermal expansion and contraction characterisitics of the steel BM and provide more than adequate impact toughness.

By homerlassy Date 04-04-2007 18:59

In Europe FCAW is used in vessel fabrication.
But only for the fill- and caplayer...and in PA-position and PF.

By js55

Date 04-04-2007 19:26

Yes, thats true. Fills and caps. You can run FCAW on an open root, played around with it a bit, but I don't know if anybody really does it in production. I'm not sure why you would.

By jiweiming (**)

Date 04-05-2007 01:48

Thanks homerlassy,js. What do you mean "PA-position and PF"?
So you indicate that FCAW can be used in Catorgory A and B weld seam of pressure vessels manufacturing? However, it only can be used in fill-layer and cap-layer, not in root-layer? Generally root-layer welding you use TIG process?Why?
Here in our country, because the filling power in the flux-cored wire is sometimes uneven and it is difficult to keep the wire from moisture(especially in high humidity condition). Moreover the wire can not be redried such as electrode consumables can.How do you keep the wire dry during using?
Your answer will be appreciated?

By js55

Date 04-05-2007 15:03

GTAW is mostly applicable for open roots, especially when ID access is limited or non existent. FCAW would be fine for a root if you used backing or were going to backgouge.
As for moisture, there are seamless wires available which are supposed to help. But help what? I've worked in shops allthroughout the american South (not exactly the Amazon Jungle but still some pretty humid places) and never known it to be a problem with FCAW wires given some simple precautions such as: purchasing hermetically sealed spools, not opening them until use is intended, covering them, or storing them in dry environments when shifts are over, even runnin a rosebud lightly over the wire in the morning to eliminate surface moisture, making sure you gases are dry, and preheating the BM before lighting up.

By George-kh (**)

Date 04-06-2007 20:43

PA and PF are European names of flat and vertical up positions. And flux cored can be used for root run, if ceramic backing is used.