Coating for A490M Structural Bolts 2

[refiner258]

Good day!

We have observed that almost all of our A490M structural bolts already have damaged coating after being installed for nearly four (4) years. We are located near the shore and we suspect that this damage was aggravated due to high chloride. Some of the bolts are flaking already. As per specifications, these bolts were coated using ASTM F1136 Grade 3. Is there anything we can use as substitute to this?

 

[SJones]

https://store.nace.org/nace-publication-02107-coatings-for-protection-of-threaded-fastener

Gives possible alternatives.

Steve Jones
Corrosion Management Consultant

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

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

 

[MJCronin]

https://www.onepetro.org/conference-paper/NACE-03252

For applications that will not be repeatedly disassembled, my vote is for PTFE coatings

MJCronin
Sr. Process Engineer

 

[dik]

For the floodway in Winnipeg, I spec'd a coating called Dacromet. You might consider this.

Dik

 

[refiner258]

@SJones, thank you very much. I cannot open the link from Linkedin (

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

Also, I wonder if there are other alternative coatings stated in NACE Publication 02107 aside from what is stated in ASTM F3125. ASTM F3125 only allows F3116 Grade 3 and F2833 Grade 1 for A490 bolts.

@MJCronin, thank you very much as well. Is the use of PTFE coating for A490 bolts already approved by ASTM Fastener Committee?

@dik, thank you very much also for your response. Based on my research, Dacromet is the market name of ASTM F3116 Grade 3.

 

[dik]

ASTM F1136 Grade 3 is correct. I don't have my notes handy, but, it is a durable coating, surprisingly thin (don't need oversized nuts) and slippery (have to watch tensioning), and, no hydrogen embrittlement.

Dik

 

[refiner258]

@dik, thank you very much. Based on your experience, how long does the coating last?

 

[dik]

how long does the coating last

How high is up? It greatly depends on the environment. These were in a protected, relatively non-corrosive environment... strength was necessary as well as longevity (A325 weren't strong enough, main hydraulic rams for the Winnipeg Floodway) I had an earlier posting on the unusual failure of the high tensioned shear failure of the bolts. Ron was the only one that noticed the unusual mode of failure, or at least commented on it.

Dik

 

[refiner258]

Ours lasted for ~3 or 4 years only. One Dacromet coating supplier was recommending to increase coating thickness to around 20 microns vs 6.096-11.938 microns recommended by F1136 Grade 3.

 

[dik]

refiner: Thanks the bolts are inspected in place. I'll have them take extra precautions. The coating was for 18-19 microns (don't have my notes handy) It was an exception to Grade 3. Thanks...

Dik

 

[MintJulep]

I have not read this in detail, but it looks interesting and informative. Master thesis, sponsired by Scania.

https://www.diva-portal.org/smash/get/diva2:441388/FULLTEXT01.pdf

There are also the following two standards that are applicable to these types of coatings.

ASTM F3019/F3019M-14 Standard Specification for Chromium Free Zinc-Flake Composite, with or without Integral Lubricant, Corrosion Protective Coatings for Fasteners

ISO 10683:2014
Fasteners -- Non-electrolytically applied zinc flake coatings

I am at the moment unclear as to the differences between ASTM F3019 and F1136 beyond F3019 must be chrome free while F1136 may contain chrome.

These aluminum-zinc flake coatings were all born as proprietary products, and the standards are relatively recent. There are "name brands" and imitators.

The materials are mundane, and the process relatively simple. But process control matters. You really don't want you bolts plated by Bubba in his shed using the same buckets he used yesterday clean his differential casing.

Also, there are a variety of top coats and modifiers that do affect the performance. You need to pay attention to make sure that you have a complete and correct call-out to make sure that are specifying what you really want and need.

I don't have F1136. However "Plate per ASTM F3019 Grade 3" is not a complete call-out.

 

[dik]

I don't have F1136. However "Plate per ASTM F3019 Grade 3" is not a complete call-out.

agreed... I had written a small spec for the product and was only vaguely aware of F1136 at the time. The ASTM Spec came up in my research on the product.

Dik

 

[MJCronin]

Refiner258 ...

As I stated above, because of their chloride resistance, PTFE (XYLAN)fastener coatings should be seriously considered..

http://www.nexussurfacetreatments.co.uk/offsite/xylan/

As you asked, they have NACE approval..... however the coatings may be costly.

Explain exactly what you mean in your original post about the failed bolting as "located near the shore" .... Is this fresh water ? Salt water ? Partially submerged or what ?

Please respect us an share your final decision and your research with us .....

MJCronin
Sr. Process Engineer

 

[SJones]

cannot open the link from Linkedin (

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

Don't worry about my Linked in profile, it's NACE Publication 02107 that is of interest:

https://www.google.co.uk/search?q=n...i60l2j69i65.3951j0j8&sourceid=chrome&ie=UTF-8

Judging by your monicker, it's not only chloride from a marine atmosphere that will be acting as a corrodent. A typical, high performance offshore platform bolt coating is:

http://www.winjoin.net/UploadFiles/file/sermagard/资料-SermaGard 1105-1280 Bolt coating.pdf

. A variant on this is to use a ceramic-metallic basecoat for the fluoropolymer.

When assessing a coating type, and the thickness to use, try to get hold of validated corrosion test results to make comparisons. Notice the claimed 5000 hour test performance of the SermaGard dual coating system. How does that stack up against the product currently under performing?

Steve Jones
Corrosion Management Consultant

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

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

 

[Ron]

refiner258....is it that the coating is flaking or are actually getting exfoliation of the bolts? I would pull a few bolts and cross section them and examine microscopically. I agree that chlorides might be an issue, but with flaking, that indicates the chlorides may be penetrating the coating....not good. Microscopic examination would also show any filiform corrosion issues that would have to do with the coating integrity.

dik...that's very kind, but I'm a product of the "blind squirrel syndrome!"

 

[dik]

same here... Dik

 

[Agent666]

Have you disproved damage due to installation being the cause/initiator, i.e. using an impact wrench to rattle the hell out of it (as they like to do) and damage/chip off the coating on the corners of the nuts/bolt heads, then in a area with a high corrosion potential its only a matter of time before it starts to break down?

I would have thought having good installation practices should all but alleviate installation damage, use of non-impact tensioning tools go a long way to maintaining the integrity of the coatings.

You didn't state where the corrosion was occurring on the bolts, or where the bolts are located in the structure (like are they washed down by rain, vs being in a hot humid sheltered environment where salts can accumulate, etc, etc).

The coatings are also not generally flexible and the threaded portion during tensioning can undergo considerable permanent deformation which can effectively destroy the coatings within the grip length (which is hidden from view obviously through the plates/hole).
See the following AISC video for some details of these points Fastener Fundamentals.

 

[BridgeSmith]

I don't know much about particular coatings, but I think an important question to ask is whether the coating is going to be applied before or after installation and tightening. I'm not really clear on that. Is the plan to recoat the existing bolts, or replace them?

For a field applied recoating on already tightened fasteners, whether it will stand up to physical abrasion, such as from wrench tightening, would seem immaterial. Resistance to chemical/weathering attack would seem to be the primary concern. I think you'll get better responses if you narrow down the performance requirements and give more detailed info on the exposure conditions.