Stainless steel cleaning and tinting question

By PFI

Date 10-31-2018 14:54

All,

I hope you can help with some definition of code compliance (Rejection criteria) in AWS D1.6/D1.6M:2017. We recently had a verification inspector reject some stainless steel components for weld cleaning and tinting on the opposite side of the material. The material is 316 stainless sheet 1/16 thick joined together with a lap joint, the tinting in question is on the opposite side of the joint and it ranges from blue to tan in color.

The only code reference I see that even comes close to this is ...

7.20.2 - Slag shall be completely removed from all finished welds. All welds and adjacent base metals shall be cleaned by brushing by brushing or other suitable means after welding is completed. Spatter remaining after cleaning that is considered harmful to the finished product shall be removed.

The word adjacent excludes the other side of the material by it's definition, as I see it. Has anyone come up against this situation? comments on experiences?

Also, the the code section above does not define what is adequate with the cleaning of the weld. does anyone have any code guidance here?

By jwright650 (*****)

Date 10-31-2018 17:14

Hi Fred,
Can you brush the tint off of the back side? I'm thinking that after the material has cooled, it should brush off fairly easy as long as you don't heat it back up when brushing.

By PFI

Date 10-31-2018 17:21

I don't think so, it's more of a "bluish" tint. I'm sure we could use a conditioning pad to remove the blue color but the areas exhibiting this would be quite extensive. This is not a cosmetic application and with the parts installed and serving would never be seen again as this is on the inside of a box like structure.

The resolve that i'm trying to get to is by code does tint need to be removed? is it recognized as a "defect" and if so what section am i missing? I can see in the section above that the weld itself and the surfaces near it need to be brushed at the very least.

By jwright650 (*****)

Date 10-31-2018 17:26

Sorry Fred,
I don't have a copy of D1.6 handy.

By waqasmalik (**)

Date 10-31-2018 17:51

Tints i guess are basically oxides formed at higher temperature by reacting with atmospheric oxygen. You can remove them by wire brush or pickling paste. Its cosmetic only. The affect is at surface only, it does not penetrates as it is in titanium,

I think corrosion resistance is compromised in the places where bluish or other colors appear. The protective chromium oxide layer is damaged there and you need to restore it by removing that tint and allowing it to form thus restoring the corrosion resistance.

By 803056

Date 10-31-2018 17:45

Heat tint isn't an issue unless the surface is wetted and corrosion is a concern. i.e. piping or vessels.

Acceptance and rejection is based on the attribute listed by the welding standard invoked by the customer/owner. It is not based on the inspector's personal opinion or what he did on his last job. The Owner is likewise bound by the acceptance criteria provided by the referenced standard unless there are exceptions taken and included in the contract documents.

The inspector should be able to direct your attention to the specific criteria provided by the standard. Otherwise, he has no case.

If the inspector insists, make it clear that his demands will be met, but the Owner will be charged for the added work. The Owner and the inspector's employer must be notified of the discrepancy and that they will be charged for the extra work involved. Then, make sure you keep a complete record of the time spent performing the extra work.

Al

By PFI

Date 10-31-2018 18:45

Al,

I believe that to be right on point! the standards / code invoked are by us the contractor. The applicable code for this application is AWS D1.6.

We do have within our standards to sand/grind down any area that exhibits a positive indication (ie. Burn through AKA "sugaring") but in this case the material is just slightly colored with no positive indications.

By PFI

Date 11-03-2018 12:55

I can only see in the code the requirement as described in section 7.20, that only requires the weld be brushed after welding, it does not required the weld to be passivized, which is the best method to restore the oxide film.

So my question is this, Is the only code requirement (when using AWS D1.6) to brush the weld only? So passivization requirements would need to be outlined in the contract documents, drawings or standards?

By Lawrence (*****)

Date 11-03-2018 17:43

Fred.

I agree with how you read it.

By PFI

Date 11-04-2018 12:23

Lawrence,

Thanks for confirming that. I wasn't sure if I was missing something.

By Jim Hughes (***)

Date 12-04-2018 11:47

PFI,
sorry I'm commenting on this so late, but AWS does have a heat tint guide. It's D18.2. Typically this guide is used by owners as an acceptance rejection criteria, at least they have in my line of work. I realize your not welding tube but it is a good reference. You might check it out.