Ball valve body cavity corrosion 1

[knowkeys]

I have an application where seawater may become trapped in the valve body cavity. The pipeline will be vacuum dryed and we want to avoid opening the valve to remove any trapped seawater.

Has anyone had experience of this type of application and/or problems with this type of corrosion.

A link to research or appropriate literature would be very useful.

Thanks

 

[RXH]

Try the following:
1. Use body drains.
2. Leave the valves in the half-open position so that the cavity is exposed to vacuum in the line.

When you state that you want to avoid "opening" the valve, do you mean avoid disassembling or avoid moving it to the open position? If it is the latter, then all you can do is drain the valves.

Alternatively, install the valves after you have hydrotested the line. (I assume you are adding the seawater for hydrotest)

 

[knowkeys]

Thanks for the prompt response.

To clarify:

The valves are remote and are only accessible by a costly intervention process. They cannot be drained.

Open means "opening" the valve not disassembly.

 

[RXH]

It looks like you will have to consider using corrosion resistant materials of construction if the seawater cannot be drained.

We have had some success with internally epoxy coated carbon steel bodies with super austenitic (e.g. UNS S31254) or duplex (e.g. UNS J32760) trim. The catch is that the coating has to be right - you need good specs, a tried and proven coating, and an experienced coater.

The other safer, naturally - more expensive, alternate is to go with full (body & trim) corrosion resistant alloy valves.

 

[bcd]

Hello Knowkeys,

This is a problem that does not have one recognized solution. Ulitmately, you will have to choose the method of protection that achieves your needs at an acceptable level of cost.

The two types of corrsion that you will have to deal with is crevice and galvanic. Both are well documented and I'm sure you can become knowledgeable on each via the internet.

It is normal to match the valve body material with that used for the piping system. Then protect surfaces where crevise corrosion will occur. Underneath o-rings, and behind polymeric seats and seals, where stagnant seawater will more aggressively attack the metal. Simple soultion like packing the seal cavities with wash-resistant grease up to expensive weld cladding is used to protect from crevise corrosion damage.

Also check the galvanic potential between the body material and the valve trim. Ensure that the potential level is very small. Materails way out on the galvanic scale, like titanium, accelerate ther ate of galvanic corrosion. This will limit the damage to the valve to just general corrosion, which should not be so severe.

bcd