Water purging in hydrostatic test 1

[serlarra]

How can I purge the water from a piping system with different diameters at the inlet and outlet after doing a hydrostatic test?

The system has a manifold that distributes the water to different piping systems. Normally we purged the water by injecting air but that didn’t remove much of the liquid.

After some reading I contacted a polly pigs supplier but they said that because of the difference between diameters they couldn’t do anything.

Does someone know another way? Will increasing the air’s pressure improve the water removal?

 

[zdas04]

I see a lot of systems with varying pipe sizes. The idiots who design them always say things like "I found an optimum solution between pipe size and pressure drop" or some such tripe. Bottom line is if you can't operate it then it isn't an optimum solution.

I'd have to see your piping to give you a recomendation, but the solutions that have worked have been:
- cut in a weld-o-let in a low point and drain the water out. Either cap the weld-o-let at the end or pipe it to surface and use a vacuum to drain it.
- use dry nitrogen as hot as they'll sell it to you and purge until it comes out dry enough (the big oilfield service trucks deliver liquid nitrogen to sites and then heat it to specification on site). This can take a LOT of nitrogen.
- use dehydrated air like the above. It can cost more to compress and dry the air than the nitrogen costs.
- go to the changes in pipe diameter and cut in pigging facilities that they should have had in the first place.

I don't have any other ideas. I've seen people spend weeks getting hydrotest water out of a pipeline that they couldn't pig.

David

 

[Jmoore1]

Ive had this EXACT problem on one of my jobs.

First we used a vac truck on the closed line to suck as much water as possible out.

Then we blew dry steam through the line until the temperature of the entire line reached ~ 300 F. Read using a temp gun.

Then we blew nitrogen through the line for an hour to ensure it was 100% dry.

This worked in a service that absolutely no water can be present and no issues occured at startup.

 

[serlarra]

Thank you for your comments; it has given me some idea of how to attack the problem. I’m thinking about sucking as much water as possible with a pump as a first step and blowing dry air through the piping as a second step. My question is: how can I know if my system is dry? How does measuring the temperature relates to the water in the system?

 

[DLite30]

Dryness is gauged by measuring the dewpoint temperature of the air coming out the vents...

 

[zdas04]

You really can't measure the dew point temperature without some really fancy equipment. What you want to measure is the water content of the inlet gas and the exhaust gas (using something like a Draeger Tube or a Water Boy). When they are as close to the same as they're going to get (up to you to decide) then you're as dry as you're going to get.

David