Using 316 electrode instead of 309

[Hosseinelahi]

I am working in a company which makes valves for sour gas. In our procedure we have to use 309 electrode as a buffer and 316 electrode for the final but the sub contractor has made a mistake and they used 316 for both layers. The final composition is in the range and no cracks were observed and the bending tests for 316/316 were also accepted. I want to know what I have to do for these overlays, are they acceptable, is it necessary to do any other test and …. I appreciate any helpful ideas and opinions

 

[metengr]

Well, you obviously have a nonconformance. I would make sure that the buffer layer weld fusion zone has been evaluated by UT to ensure no cracks or other weld defects. If the weld fusion zone is sound by UT what you have is a region of 316 weld deposit that is sandwiched between the substrate and 316 corrosion resistance weld overlay. If you duplicated this effect using a coupon and were able to pass bend and tensile testing along with the UT, you should be able to disposition as acceptable for use. Run this information by the client and see what they say. Also, you should have this nonconformance handy so that purchasers know that this was a nonconformance and it has been dispositioned.

 

[jwhit]

If you are overlaying on carbon steel the 309 buffer layer serves to take care of any dilution that may occur on the first pass or two by the carbon steel. Having said that, I would suggest that you make certain that the final layer chemistry meets that of 316 electrode. You may well have diluted the 316 down to the point where it is forming a martensitic surface rather than a highly corrosion resistant austenitic stainless surface. The issues can be much bigger than cracking and poor ductility.

 

[EdStainless]

What is the service temp?
In long term at high temp C will diffuse more rapidly through 316 than through 309.
316 may (depending on chemistry) be more prone to formation of detrimental secondary phases (sigma).

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metengr]

If the final corrosion resistant weld overlay is specified as 316 stainless composition based on service requirements, the above concerns are irrelevant. If the concern was simply use of 316 versus 309 for the intermediate layer and the bend testing was acceptable obviously dilution to cause harmful phases is less of a concern.
If the external weld overlay meets the chemical requirement for 316 stainless, sigma formation will not be an issue. Sigma is going to happen throughout the entire overlay because the material originally selected was 316.

 

[jtseng123]

If I am the buyer, and yes I am the buyer all the time, I will reject the valves, peroid. How are you going to prove to me that for sour gas service, and at specific design temp and pressure, nothing will happen ? Does bending test, tensile test, UT test, composition test mean anything ? I don't think so. You will need to prove to me, for runing 10 years at the design T and P, it still have the resistant property.

 

[SJones]

I'm with you jtseng. If a simple screw up like that occurs what other simple mistakes have been made? At the very least, you would be into several months of corrosion testing to prove acceptability. Quicker to start again, or go somewhere else.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[stanweld]

The after the fact qualification of the procedure does not prove that the production item's first layer is not martensitic or partially martensitic. I'm with jtseng and Steve on this one. Scrap it, repair it, don't ship it, don't receive it!

 

[ornerynorsk]

Some things are best chalked up to the school of hard knocks. What might seem like an expensive education in scrap now could very well turn out to be cheap insurance and a reprieve from a much worse event.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[kadinExpert]

Preventing from hot cracking in the final layer is the main purpose of using 309L electrode for the first layer. Therefore using 316L electrode for the first and second layers could increase the risk of cracking in final layer. If you have done PT test for overlays then you don’t have to worry about the quality of the overlays. But you should consider the chemical composition of the final layer because 316L electrode has less Cr and Ni.
Having used 309L electrode in the first layer, martensite phase was also formed (according to my experience) near HAZ. However, after welding the second layer this phase could be tempered. Since the bending tests met the standard requirements, I think mechanical testing and martensite are not the main concerns.

 

[LuWang]

I completely agree with Metengr and Kadinexpert, the risk of using 316 instead of 309 for the first layer is for producer because of increasing the possibility of hot crack formation in the final layer. Hard phase (martensite) has low carbon so it is not dangerous. But check the composition because the Cr and Ni in 316 is less. If Cr and Ni is ok accept the valves with some discount.

 

[mfgenggear]

Under Rejection Material Review Authorization (RMRA) or Material Review Board (MRB), why not cut out the discrepant weld,
then re-weld a new section is slightly longer to allow for weld shrink & parent material consumed.. This a standard repair when the weld is FUBAR, and not repairable. Eliminates if this is issue or not.

Mfgenggear