Painting on Cold insulated piping

[shiny2012]

Dear Sirs,
We have a Low temperature piping but it was not insulated. The pipe was painted with Zinc based paint. Now we are planning to insulate the pipe using Cold insulation. Is there any chances of "Corrosion under insulation". The design temperature is (-50 Deg. C). Please give your opinion. The piping is curently in service. Piping material is LTCS (A333 Gr.6)
Regards
Shiny

 

[LittleInch]

In a word yes. Paint is not normally recognised as an anti corrosion coating when subject to near continuous water / ice and lack of easy inspection which is what you will have when you insulate it unless your insulation is very good. What type of insulation, is it above ground, what is your normal operating temperature?. It will be a lot better than hot pipes less than 100 c, but unless you strip off the paint, blast clean and spray with a high integrity, high build coating, you will have such a risk, especially at flanges, supports and offtakes.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SJones]

Equipment that operates continuously below -4 deg C usually remains free of corrosion

Try studying this standard, particularly footnote E to Table 2, to gain an insight into what you might do with the existing coating.

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.

 

[LittleInch]

I agree, if it's permanantly below zero or -4 C then you will prob be Ok, but the issue is when it keeps varying above or below freezing and also any parts which extend out from it like flanges and offtakes which might sit at low temps, but not below zero C.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SJones]

Quite, but it's all covered in NACE SP0198. I could throw in EFC Publication 55, but that's probably pushing it for this thread.

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.

 

[shiny2012]

Dear Sirs,
Thank you very much for your replies.
It is an existing piping. The operating Temp is (-27 Deg. C). It is in use for around two years. It was considered as intermttent service piping initially. Now it is going to be a continuous service piping as we are going to tie in with another pipe. No change in service conditions. As it was considered intermittant service no insulation was provided and "Inorganic zinc rich primer + Micatious iron oxide epoxy + Polyurethane enamel" was applied. It is an above ground piping running on a pipe rack inside the plant. As it is in the running plant we can not remove the paint. For installing another new piping require shut down and is a lengthy process.
So we are thinking of applying cold insulation with out removing the existing paint.
In case of new piping insatalled, what kind of painting shall be applied before installing the cold insulation?
Please give your openion.
Regards
Shiny

 

[chicopee]

Commercial zinc based paint, then insulate. But before you coat, speak with the paint company representative of your plan and he/she may suggest a particular paint system.

 

[sentjoh]

Apart from the coating, the insulation system you design is also of influence of possible CUI failures.
I would like to recommend the CINI manual for industrial insulation, which has a detailed specification for cold/cryogenic insulation:

http://www.CINI.nl

If you are planning to insulate on a live running pipe I’m wondering whether you need to cope with icing on the pipe. If so I assume you need to remove this before start lagging. I can recommend to use a petrolatum gel on the pipe prior to start installing your fist insulation layer. This gel gives you a time window of a couple of minutes in which no icing on the pipe will occur.

Since it’s an existing pipe that wasn’t insulated I also would pay special attention to the pipe-supports. Can they accommodate the needed insulation thickness? I also would recommend if possible to install cold-bridge free pipe supports.


Regards,

Johan Sentjens

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