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CountOlaf (Mechanical) (OP)
14 Nov 07 16:55
I'm posting a duplicate query here as well just in case you guys don't visit the "piping and fluid mechanics engineering" forum.  Someone there suggested a welding forum, but I don't think there is one of those.  Anyway...

Is it OK/common practice to weld 316L SS pipe to standard sch 40 carbon steel pipe or A36 steel plate?  Are there any type of special welding materials/electrodes or special prep procedures that I should call out on the drawings/in specs?

Also, is there a dielectric issue with these dissimilar metals?  I don't have water in the system.  The application is more of a stack instrument test port nozzle.

And finally, if flanging/gasketing is employed, doesn't the gasket serve to dielectrically separate the two materials or do I need something else since the bolting bridges the materials?

Thanks in advance.
metengr (Materials)
14 Nov 07 17:06
Dissimilar metal welding is done provided the corrosion environment is evaluated (aqueous versus dry atmosphere) as well as elevated (at or above 800 deg F) temperature service.

If corrosion is not an issue, the filler metal for joining the dissimlar metals is either 309 or Inconel (if the joint is exposed to elevated temeprature service).

I would use an AWS or ASME Section IX qualified welding procedure. The weld prep will depend on load conditions - you can fillet weld or use a partial penetration groove weld. Nondestructive testing (using Liquid penetrant) should be performed after the welding
gr2vessels (Mechanical)
14 Nov 07 21:06
For electric isolation, use standard bolting insulator sleeves.
cheers,
gr2vessels
strider6 (Materials)
15 Nov 07 10:32
It's common practice, at least in my experience, to use a buttering layer of filler material, eg 309SS, on the Carbon Steel and then to weld to the SS 316.
Look also at  "welding of stainless steel and other joining methods"  NIDI  pub no 9002, there is a chap on dissimilar welding.
http://www.nickelinstitute.org/index.cfm/ci_id/11931/la_id/1.htm

Regards

S.

http://www.corrosionist.com

metengr (Materials)
15 Nov 07 10:46
strider6;
This practice only applies IF PWHT is required for the CS. Otherwise, I see no benefit to be gained by buttering.
strider6 (Materials)
15 Nov 07 11:08
i agree with you on the PWHT, but one benefit could be that you can NDT the buttered layer and then perform a SS to SS welding instead that a Carbon Steel to SS.
Also as reproted on the cited pub of NIDI "the portion of the joint where difficulties are most likely to occour is buttered while there is little restrain on the weld metal.."
So in my opinion butter is always a "good practice", and if i have to prepare a wps i'll include it; also 'csue the requirement for PWHT are not always the same and in this case i don't know the thickness involved.

S.

http://www.corrosionist.com

CountOlaf (Mechanical) (OP)
15 Nov 07 13:39
Thanks for the advice thus far guys.

strider6:  do those articles at the "nickel" website cost, or is memebership free?  I see a lot of "order by mail" stuff, but the pdf's seem pretty small.

Olaf
JasonLouie (Materials)
15 Nov 07 13:47
Information from the Nickel website is free.  You can download the pdf's without membership or cost.  Some of the older documents are not electronic in which case they will mail it out to you.

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