welding 304 with 316 1

[StoneCold]

I walked into a project today where they were socket welding 2" pipe. They were tig welding the sockets which is a little odd in it's self but they were also welding the 304L pipe with ER 316L filler rod. I advised them that you would normally stick weld the sockets and that if you were going to tig the socket that the apropriate filler metal would be ER 308 or ER 309. Do you think there will be cracking at the root of the welds made with the 316L due to filler/base metal differences?

Thanks
StoneCold

 

[metengr]

StoneCold;
GTAW welding of stainless steel socket welds is very common. The filler metal selection is fine, ER308L is typically used. The key to avoid cracking in the weld root is to assure you have an adequate gap on fit-up (1/16" min).

 

[EdStainless]

The other key is have a material a bit of ferrite on solidification. Just about any 3XX filler will meet that criteria.
The only real problem is that they are using filler that costs a lot more than they need.

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[robsalv]

Edstainless/Metengr, would you recommend minimum two pass fillets??

In my understanding, GTAW is "better" for welding stainless because the heat input can be better controlled. Thing is, where I work, it's our "common wisdom" to be suspect on welder GTAW technique with respect to root penetration and sidewall fusion, and will radiograph greater than minimum % of GTAW'd weld. In the case of SW's, we look both for minimum gap and for tell tail LOF.

Cheers

Rob

 

[GRoberts]

GTAW welding has either less or more heat input control depending on your definition of control. If by control, you mean that the welder has more flexibility, then yes, there is more control with GTAW. If by control, you mean that a heat input per inch of weld can be controlled better, then no. You can get carried away with high heat input with GTAW welding if you are not set up right, or the welder is not experienced or does not use good technique. That is because heat input is indepenant of filler metal addition. In SMAW for instance, you are guaranteed that two beads of the same size were made with approximately the same heat input. Not so with GTAW.

It is also true that with improper welding techniques, it can be difficult to get complete penetration to the root of a fillet weld, but in my experience, GTAW welds should have less defects per inch of weld than most other processes if done properly.

 

[stanweld]

ER316L is often used to weld 304L material and can provide superior corrosion resistance; however, in some corrosive environments it may be highly detrimental (most notably in environments subject to metal dusting of 316). ER308 is the more economical choice especially when taking into account today's high molybdenum cost.

We almost exclusively weld stainless steel sockets with the GTAW process. The leak incidence using SMAW was simply too high due to poor welding technique at the tie-in locations.

 

[EmilGies]

Were they following a WPS and what did it call out for filler?

 

[stanweld]

We weld 304L socket welds with ER308L filler metal, unless the owner/engineer requires ER316L and we have had a number of instances where it was so defined. Written procedures, qualified per ASME IX are used. The problem with SMAW simply invoves welder technique and proper welder training to assure sound welds; unfortunately, field management will not provide the appropriate training because "its just a socket weld and any qualified welder can do it." All of our GTAW welders are qualified for "open root" pipe welding and have no problem making sound, leak tight socket welds. Well trained welders make sound welds repeatedly.