Corrosion on Welded Shoes on Cold Line

[uaepiping]

The supports on a cold fluid lines are provided outside the insulation cladding. Below this cladding is PUF type insulation blocks, vapor barriers (to avoid any moisture ingress to pipe's cold surface). The supports are clamped type installed on the cladding. The support steel resting on structural supports (rack, sleeper or structural supports) does not have any contact with the cold pipe.
In one of our plants support shoes on a 10" insulated lines were noted to be corroded (almost 200 supports on the line). The problem is that 10" line is cold line (13°C operating temperature). The supports were directly welded to pipes and the line was insulated after that. This caused CUI and all those supports got corroded. Due to insulation the line condition cannot be seen.
We proposed to
1) Inspect the line and decision to be made to replace the pipe based on extent of corrosion.
2) If pipe is ok, cut the supports as near as practically possible,
3) Provide cold PUF insulation and vapor barriers as per specs for cold line insulation at support locations,
4) Provide clamp type shoes on support locations.
An opposing opinion among the piping team is given that cold support vendors may have some solution which may not require changing of whole 200 plus supports.
I don’t think anything can be done to avoid proper supports. But what is your opinion/experience in such case?

 

[MJCronin]

I believe some picture would help here.... especially around the pipe supports.

Is this a system exposed to salt water or marine environs ?

MJCronin
Sr. Process Engineer

 

[fatih.fidan]

I believe that corroded occurred by external effect like as MJCronin mentioned marine environments.

As per my experience from our cryogenic plant projects, 13°C operating temperature is a high temperature for cryogenic insulation. I mean it is not feasible. Of course You can do it, but it will huge cost impact, so eliminate crypgenic support option would be better for your company.

The first solution to come my mind is passivation if steel is stainless steel. Firstly, you should do passivation, and after that you must paint properly according to project job spec or environment needed. I am not paint expert, but paint selection is very important especially in marine environment. Please not that if effect is very big your pipe support to working properly, you should remanufactured pipe support. I hope damaged is not to big, because if remanufacturing pipe support needed, pipe shall be hydrotesting after pipe support welding. If pipe is carbon steel, you should fix damaged properly and then paint properly. Additionally for carbon steel, some special product may clean corrode. You can use for cleaing CS steel material.

Note: As I said before, painting is very important especially for marine environemt, so maintanance teams should always check painted components or steels, and they have to repaint when they see any fault or corrode.

 

[LittleInch]

You state there is CUI (corrosion under Insulation), yet then claim the line condition can't be seen -??

I think you mean that the cold nature of the shoe has attracted condensation on a continuous basis and over time this has corroded the pipe supports - correct?

So if the pipe supports are corroded then you can replace the supports and make sure you coat them effectively against water and corrosion.

But it all depends where the corrosion is, what type of support you have and where are you getting abrasion and what the cost impact is to do it properly as you describe, or just fix it as per your colleagues



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

 

[georgeverghese]

Must say this is a very common problem in the industry. No one seems to pay attention to pipe supports during detailed design, leaving Operations to carry this jerrycan for this life of the facility.

 

[uaepiping]

Fatih, the environment is saltish, hot, humid on shores of UAE.
Littleinch, you are right.
13°C is a cold temperature where the summer peak can be 55°C and even in winter the temperature during daytimes is around 18-20°C.
Moisture accummulation at pipe is must due to this.
Line material is LTCS.

 

[uaepiping]

@MJCRONIN, the sketch may help in visualizing.

 

[MJCronin]

UAE .....

Were the pipe shoes purchased galvanized ?

Were they supplied with a brown "zinc rich" coating in anticipation of painting in the field ?

Galvanized pipe shoes are the default configuration commonly specified.

https://pipingtech.com/products/pre...cGzQ23LvBtdOr_YWM0O9vxwYsfX-wz4BoCQLAQAvD_BwE

MJCronin
Sr. Process Engineer

 

[weldstan]

You don't state how badly the supports are corroded. Can they be cleaned and recoated with a cold galvanize or aluminized coating? Are they so corroded that they are structurally unsound?

 

[uaepiping]

The pipe shoes were painted. (I am not sure of Zinc rich coating).
@ WELDSTAN,
Point here is that though structurally the supports are still adequate, but the water due to moisture condensation will again corrode.
So you are suggesting to apply "Aluminized Coating" on the supports. Question is:
Will it resist corrosion due to condensed water?