Flange coating damage 2

[Gorik]

Hi,

Recently while walking on site noticed some damaged coating on the flanges (see photo). Guys told me that it is the common issue after torquing. They making some field repair, though it's still more prone to corrosion. So, maybe I could get some advice on how to mitigate this. Maybe some washers would help to distribute the load and minimize friction from the nut. Flanges designed acc. to ASME B16.5, assembled acc. to ASME PCC-1.

Thanks!

 

[TugboatEng]

Ideally, a zinc rich coating will protect minor areas of damage due to assembly. Spot repairs after assembly are better still.

However, your coating does not appear to be well adhered to the substrate. You need to address the initial application before proceeding further.

 

[LittleInch]

What's the coating? It looks really quite thick. The coating needs to be capable of withstanding nut forces.

Can't recall seeing such a thick flange coating

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Krausen]

Yes, washers would help with this issue. It never hurts to have thru-hardened washers with your flange bolting, per ASTM F436 spec.

 

[SJones]

IOGP S-715
"Nut bearing area and bolt holes shall be left uncoated or only coated with primer coat prior to installation, if coating is required."

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[r6155]

See "LUBRICATION OF “WORKING” SURFACES", in ASME PCC-1

Regards

 

[desertfox]

Hi Gorik

From my experience coatings nearly always get damaged around bolted joints and to my way of thinking if it’s a huge concern then the flanges/ nuts could be coated or painted after assembly similar to touching up scratches on your car.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[r6155]

Various problems are possible and can cause paint damage.
1) flange misalignment and extra torque applied
2) No lubrication on the contact surface of the flange and the nut
3) roughness defects in the flange
4) this is not an ASME B16.5 flange
5) The light thickness of the flange is not compatible with the diameter of the bolt.
6) Is a spacer installed on the bolts? View photo.

Regards

 

[LittleInch]

I think it's a wafer check valve or a butterfly valve between flanges.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

1) Hi SJones
You mentioned “nut” but (0P) is about the “flange”.

2) Hi LittleInch
Yes, is a valve between flanges.

Regards

 

[Gorik]

Folks, thanks for all replies!

Additional info that I forgot to mention on original post.
1) It is butterfly valve on the photo.
2) Studbolts and nuts should be lubricated (Molycote 1000) as per internal spec, though need to recheck with guys on site if it was done.
3) Flange misalignment and extra torque applied is highly unlikely (internal inspection throughout installation process).
4) It is common issue, so it is no defect.
5) It is ASME B16.5 flange.
6) I'll check the coating info, which it was and was it the same where the problem occurred.
7) IOGP S-715 requirements fits, maybe we should make some rev. of specs.

 

[3DDave]

A washer prevents the nut from applying a tangential shear load to the paint; the shear capacity of paint is much lower than metal. When the joint comes to full tension there is also a shear load normal to the surface where the nut contacts the paint, which also can fracture the paint. A washer will help by flexing so the load at the edge of the washer is much lower.

It also appears to be possible poor paint prep that has allowed damage from under the nut to progress, separating from the surrounding area. If the paint was merely brittle it would fracture at the nut and be done. However the paint looks sturdy and that may mask the adhesion problem with typical paint adhesion testing. It probably needs a test where a metal sample is bent over a mandrel.