Not logged inAmerican Welding Society Forum
Forum AWS Website Help Search Login
Up Topic Welding Industry / Technical Discussions / Filler Metal for 25 Chrome 8 Nickel Pipe
- - By NDTIII (***) Date 07-24-2007 03:34
We are welding some 25 Chrome 8 Nickel Pipe (A 790) and Inconel fittings. . The service is salt water for a RO plant. Pipe diameter is 6", 10" & 14", all Schedule 40. Operating pressure is 1000 psi. We are welding 25 Chrome 8 Nickel to 25 Chrome 8 Nickel Pipe and  25 Chrome 8 Nickel Pipe to Inconel Valves.

My question is, is ER-316L wire suitable for welding this application? If not, what would be a suitable filler metal?
Parent - - By MBSims (****) Date 07-24-2007 04:06
Exactly which grade of duplex stainless do you have?  2507?
Parent - - By NDTIII (***) Date 07-24-2007 04:46 Edited 07-25-2007 03:26
It is A790 materal UNS number S32750. Does that help?
Parent - By chuck meadows (***) Date 07-24-2007 19:48
S32750 is a Super Duplex material  (2507)and Avesta makes a filler metal, P100, that is designed specifically for welding the 2507. This steel has very high mechanical strength and very resistant to general corrosion, intergranular corrosion, pitting corrosion, but is origionally designed for it's great resistance to chloride stress corrosion cracking capabilities. Usiing a 316L filler metal will reduce the strength, chloride stress corrosion capabilities, and will lower the ferrite percentage in the weld metal. I will gladly send you a couple of papers I wrote, one for NACE and the other for general information when welding 2507, if you will send me your e-mail address.

Chuck
Parent - - By Noel Tan (**) Date 07-24-2007 07:11
i'm not sure why u choose to use austenitic SS filler metal on ferritic/austenitic duplex SS. Generally, weld produced by austenitic SS shall has a lower pitting as well as stress corrosion resistance against duplex. if 316L is fit for service requirement and why duplex pipe is used? most of the WPS qualification of duplex required ferrite content to be measured, i don't think 316L can satisfy this requirement. --- just personal opinion.
Parent - - By NDTIII (***) Date 07-24-2007 07:28
Thanks Noel. I did not choose this material. I just performed PMI on it and found out what it was. We also radiographed 2 joints and found LOP 360 degrees in both joints.
My concern is when they fire this thing up, will the welds hold.
What type of filler metal should have been used?
Parent - - By Noel Tan (**) Date 07-24-2007 07:46
PMI performed on weldment shown 316L doesn't means the filler metal used was 316L (of course it may be 316L)...chemical composition for weldment may changed due to dilution.

http://www.incoweld.com/HTML/appendix_main.htm
this website may give u some recomendations for selecting filler metal.
Parent - - By NDTIII (***) Date 07-24-2007 07:56
We know he used ER-316L. WE did the PMI on the pipe because we were told that was S/S, but it turned out to be 25 Cr.
Parent - - By Noel Tan (**) Date 07-24-2007 08:42
Actually i don't know how to select material for a specific service, if u ask me i would prefer duplex for salt water because of beter pitting resistance (normally PRE>40) and stress corrosion. In the standpoint of welding, the weld shall be produced as close as possible to the parent metal (as specified in design drawing) in term of mechanical properties as well as corrosion resistance. if design called for duplex i will not accept welding with 316L as a welding engineer. i couldn't help u much on this issue. :(
Parent - - By NDTIII (***) Date 07-24-2007 11:07
You helped more than you think. Thanks
Parent - By js55 (*****) Date 07-24-2007 13:34
There is no secret method to choosing materials for service. In the end its an educated guess. Though for familiar services a very good one. The problem with corrosive services is twofold. First of all every corrosive service is unique (even seawater from different parts of the world have different chemistries that react differently on different materials), second of all, all of the corrosive test methods are short term methods (G36, G48, etc.) extrapolated to long term service. So in the end, you estimate. Thats why failures pop up from time to time.
As for your situation with 316 my 'guess' would be that it will hold up for a short period of time and then fail first by leaking though not catastrophically. But bottom line I think someone screwed up. Tan is right, there needs to be some effort at either matching or overalloying with corrosive sercvices in the face of the twofold doubt. And in this case it didn't happen.
Parent - - By chuck meadows (***) Date 07-25-2007 00:51
Your personal opinion is very true. Using a 316L filler metal (generally around 5-10 FN) will likely lower the FN of the weld metal that is normally required by most Engineering specifications for a duplex fabrication.  Also, the weld process will definitely have a very  big effect on the FN of the weld metal. Any weld process such as SMAW, FCAW, and SAW, due to the oxidation in the flux, can lower the FN. But, regarding the use of 316L as a filler metal for Duplex is normally not recommended or  allowed. Like you said, if 316L is fit for service, then duplex is a big overkill. The stringent testing on most duplex fabrications have levels that the 316L cannot satisfy. Your points are well spoken and well taken.

Chuck
Parent - By NDTIII (***) Date 07-25-2007 03:50
My thanks to everyone. Alot of good information. It really helped.
Up Topic Welding Industry / Technical Discussions / Filler Metal for 25 Chrome 8 Nickel Pipe

Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill