Preservation of inactive piping

KevinNZ · Sep 19, 2021

Hi all

We have a few 100m s of above ground DN600 carbon steel piping to mothball for a few years. The line is normally used for steam and water.

What are the options for Preservation? We are looking at low flow nitrogen purge or bleed of steam into the line. Are there chemical options we can look at too? Vapor Corrosion Inhibitor (VCI)? Just fill it with water and Corrosion Inhibitor? Just seal it up?

The line has been service, so may have some light scale and/or corrosion products.

Thanks

pmover · Sep 19, 2021

assuming low pressure design . . .

recommend N2 purge and monitor N2 pressure during mothball stage.

check for leaks after initial pressurization & repair any leaks. 5-psig N2 should be sufficient. Continue to monitor N2 pressure.

good luck!

GD2 · Sep 19, 2021

KevinNZ,
Usually Pipeline Regulator prescribe the following rules for discontinuation:
1. Physically isolated or disconnected.
2. Cleaned if necessary.
3. Purged with fresh water, air or inert gas - any of which may contain corrosion inhibitors, if Licensee is prepared to mitigate an accidental release.
4. Protected by suitable internal and external corrosion control measures.

GDD
Canada

EdStainless · Sep 20, 2021

I would suggest the use of VCI and N2.
The VCI will coat the surface and might lessen the N2 required to keep things dry and clean.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

TugboatEng · Sep 20, 2021

Inhibitors require a clean surface so you would need to acid wash the pipe prior to use. A dry layup with N2 is likely simpler.

KevinNZ · Sep 20, 2021

Thanks

Should have added that we also need to consider external corrosion. The line is outside and insulated.
Using steam keeps the outside hot and no different to an operating line. Do have to pay for the steam. There is also some interesting steam chemistry to consider (concentration of non-condensable CO₂ and H₂S)

pmover · Sep 20, 2021

with external protection now being considered, is this pipe worthy of temporarily being decommissioned vs removal and replacement?

typically, steam pipes are insulated and cladded to prevent impacts by ambient weather.

consider a shrink wrap for external protection.

LittleInch · Sep 21, 2021

Kevin,

what do you mean by "steam and water" - Is this steam and some condensate?

What is the current external anti corrosion coating or insulation system?

How easy is it to drain this line and vent it / blow it / dry it?

That will tell you whether to go for a dry system with Nitrogen at a low pressure you can check and maintain or inhibited / oxygen scavenger / biocide fill instead.

One issue with Nitrogen filled lines in a plant at that size is the risk of asphyxiation if it leaks or someone opens a valve thinking the line is redundant.

Can't advise much on the external corrosion until we know what the current situation is.

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

HTURKAK · Sep 21, 2021

The following link may help you ..

https://www.piping-world.com/piping-pipeline-preservation-mothballing-lay-up-after-testing

KevinNZ · Sep 21, 2021

When in operation the line carried two phase steam and water.

External corrosion is not a problem for operating lines as they are hot and no moisture on the external surface under the insulation and cladding.

We can drain the line and dry it. Low pressure nitrogen is the first option we are looking at. Next option is keeping it hot with steam.

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Preservation of inactive piping

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