Surface protection for Bolts A193 B7 and B16 1

[Matteo_87]

Hi everyone,

I am currently designing piping for an HRSG falling under ASME BPVC section I (for boiler proper), and ASME B31.1 (for both boiler external piping and non boiler external piping). In the piping system I have some flanged connections, where the flange is either in A-105N or A-217 WC9. The whole piping will be then insulated.

My question is: what is the best surface protection for the bolts of these flanges (A193 B7 and B16)? Is it better to leave them "black" or to galvanize them?

Thank you

Matteo

 

[metengr]

Do not galvanize, the metal temperature for these bolts will be well above the temperature suitable for galvanizing.

 

[TGS4]

Think twice about insulating your flanges.

 

[r6155]

See Appendix X2 in SA-193 and SA-194.

Regards
r6155

 

[Matteo_87]

Dear r6155,

thanks for the tip about appendix X2 in SA-193 and SA-194. Based on that, it is recommended not to use zinc coating if the temperature exceeds 210°C

I have two questions about it though:

1. I assume that the temperature to be considered shall be the operating temperature of the bolt itself. However, is it safe to consider the design temperature of the flange itself?
2. If the temperature is above 210°C, should I but black bolts without any surface protection?

Thank you again

Matteo

 

[XL83NL]

1. The most conservative approach would be, and thats how we deal with our PTFE (Xylan 1070) coated studs and nuts, is to use the design tempeature (from your PID) as the limit. That way you have some margin. Example; if the PID design condition is 210 °C, you can use zinc coating. If the PID design condition is > 210 °C (regardless of operating temperature), you cant use zinc coating. Bear in mind that for future purposes, the operation conditions may be altered. As a consequence, when someone doesnt review the items of the altered system (simply because he/she assusmes that everything meets the design conditions, and as such dont need review), one can go beyond the 210°C-threshold in the case when the design condition is greater than 210 °C, but the initital operating conditons wasfar lower, say 140 °C.
2. Above that temperature, to my awareness, there arent much other coatings available. PTFE coating goes to 230 °C. Of ourse you will use a high temperature paste like OKS 250 or whatever, but other than that, there's not much avaliable for coatings.

*) Furthermore, I would not push it to the limit, and set some margin between what X2 mentions, and what your spec ultimately calls for. So use zinc coating e.g. up to max 200 °C design.

 

[SJones]

The need for bolt coating should be ascertained by a risk assessment of corrosion under insulation (CUI) for the design & operating conditions, the selected insulation system, and the insulation configuration. Should the corrosion risk assessment result in bolt coating being deemed necessary, then there are several established high temperature coatings, generally based on ceramic materials, such as Praxair SermeTel type, or Magni 595 type.

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.

 

[r6155]

Insulation specifications are critical requirements.

See:
NACE SP0198 Standard Practice
Control of Corrosion Under Thermal Insulation and
Fireproofing Materials—A Systems Approach

American Galvanizers Association

https://galvanizeit.org/

Regards
r6155

 

[EdStainless]

What are you using to protect the piping?
Cold spray Al has been used to provide sacrificial CUI protection for piping, but I am not sure about upper temp limits.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

SJones is correct.

 

[MJCronin]

I agree with Mr. Jones .... The bolt coating decision is part of the CUI for the piping system

A discussion of insulation/protection on flanges may be found here:

https://www.eng-tips.com/viewthread.cfm?qid=424724

MJCronin
Sr. Process Engineer

 

[Matteo_87]

About pipe protection, the specification from our client mandates the following:

For design temperature lower than 400°C, 60 micron of zinc inorganic primer followed by 30 + 30 micron of silicone aluminum

For design temperature higher than 400°C (max 540°C), 30 + 30 micron of silicone aluminum only

In our case, flanges will be covered by removable insulation box

Do you have any applicable standard to perform the CUI analysis?

Thanks,

Matteo

 

[BJI]

There is a bit of misleading information in that link regarding flange insulation. IMO it is generally not recommended to insulate flanges, only under specific process conditions would it be worth the risk.

 

[r6155]

See Hydrocarbon Processing april 2018 "Optimize your insulation to reduce cost".

Regards
r6155

 

[r6155]

The specification from your client is for pipe protection. Must be clear for bolts

SA-193 3.2 Coatings—Coatings are prohibited unless specified by
the purchaser (See Supplementary Requirements S13 and S14).
When coated fasteners are ordered the purchaser should take
special care to ensure that Appendix X2 is thoroughly understood.

Regards
r6155

 

[Matteo_87]

I checked the version of ASTM A-193 we have in our company and it is 99 version (quite outdated). In the old version there is no mention about coatings

Do you know what is the most updated version and where I can find it?

 

[XL83NL]

If you need to work to BPV sec I, you should have ASME BPV Sec II in place as well; the current (for work under ASME BPV approved) version of A193 is in sec. II-A.

 

[Matteo_87]

Thanks for the tip. I found the updated version in ASME BPV Section II