Valve types - pockets

[rscosta1976]

Good afternoon,

I'm not a valve SME and would appreciate your thoughts on the issue below.

During hydrotesting of plant piping circuits tested with valves already assembled, some valve types are prone to excessive water accumulation that can hardly be drained following the pressure test. Unless the valve is equipped with drain plug, which I believe only exists for big diameter valves, excessive corrosion of valve internal components can occur due to water being accumulated for long periods of time.

For these cases and depending on valve trim material and lay-up or preservation requirements implemented following the hydrotest, some valve types are more prone to corrosion to occur, as not all hydrotesting fluid (usually water) can be successfully drained. This is usually a concern for new projects, where several months gape can exist between hydrotesting and start-up dates.

Your help would be appreciated to list the valve types more prone to accumulation of liquid pockets and the ones where this would not be a problem flowing the hydrotesting of plant piping.

Thank you

 

[LittleInch]

I think they all have some sort of pocket tbh.

Most procedures require valves to be partly open during a test to avoid having air pockets and voids which allows the liquid to fill the valve.

I would have said most valves other than really small ones have a drain plug though.

It makes it very important to dose your hydrotest water with biocide and oxygen scavenger to avoid this. There have been many failures of plants due to river water being used without dosing it and then sitting in low points for months i hot weather and the SRBs getting to work eating the pipe and valves. Keeping it under pressure in Nitrogen would also help reduce corrosion risk.

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

 

[rscosta1976]

Thank LittleInch,

I share your concerns regarding proper water treatment for hydrotesting water and lay-up requirements to be mandated afterwards. We have strong requirements for this, but in same cases we've still detected excessive corrosion of valve trims (especially 400 series and some 300 series) before start-up.

I believe some valve types are more prone to water accumulation following hydrotesting than others, even in case dry air is used to blow the piping circuit.

In your opinion, what would be the valve types more and less susceptible to this phenomena?

 

[LittleInch]

Gate valves aren't great or plug valves. Ball valves shouldn't be too bad as the seal areas keep out of the water.

But some places remove valves for hydro due to this reason and replace them with spool pieces then replace and do a leak test to prove the gasket sealing.

Can be sen as an excessive cost, but prob saves you money in the longer term.

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

 

[rscosta1976]

I agree that removing valves prior to hydrotesting is the best approach. We implement this measure as far as practically possible. However, there are many valves that cannot be removed (or are not practical to be remove), including welded ones. For those it is not easy to find efficient protective measures following hydrotesting, especially if these are not equipped with drain plugs.

Thank you very much for your insights on this subject. I truly appreciate it.

 

[The Obturator]

'Back in the day......' after we hydrotested, we simply aimed a heating blower to the valve outlet until the inside was dry. This took 30 - 45 minutes depending on size etc. These were Pressure-relief valves which can also accumulate water etc., in pockets and crevices. Once dry, we reapplied some mineral or soluble oil fine spray to the inside of the valve (if it was carbon steel). Normally, during initial assembly before testing, we would apply a mineral/soluble oil spray to the inside of the valve body and bonnet just to prevent oxidisation after shipping. This was for general service valves where such oil coating would not be detriment to the intended process. It's also recommended that the valve openings are sealed off afterwards (flange protectors etc.).

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the ASME/API used term ***