New pipeline construction - corrosion inhibitor 2

[Sam066]

Hi all,

Is it recommended to run a batch of corrosion inhibitor (oil-based for instance) after hydrostatically testing a pipeline with a water/methanol mixture in case the pipeline commissioning is delayed or a pipeline drying may be sufficient to get rid of the water/methanol mixture?

Thank you,

Sam

 

[pmover]

How long? send sponge pig(s) down the length of p/l to aid in removal of methanol/water mixture.

-pmover

 

[Sam066]

Thanks pmover,

It's a fairly long pipeline & big inch, but the pressure and drying are done on sections of pipe anyway.

I'll reformulate my question: Because of the use of a water/methanol mixture during the pressure test, and as the drying may not allow us to get rid of all water/methanol, would it be better to run a corrosion inhibitor batch - provided of course it's done efficiently - to make sure that no water/methanol remains in the pipeline?

Sam

 

[zdas04]

Methanol is some really interesting stuff. A 50-50 mixture gives you really good freeze resistance which is why it is added to hydrotests. It is also deadly to anaerobic bacteria (the kind that give you corrosion in steel pipes and can lead to H2S developing), and it tends to coat steel to inhibit general surface corrosion. If I had to do a hydrotest on a line that wasn't starting up for a few weeks, I'd just leave the line full of water/methanol mix and dewater it just before commissioning.

Most stuff labeled "corrosion inhibitor" (as opposed to "surface treatment" or "paint") is intended to be run along with process fluids and wants to be in a continuous phase liquid. Pigging in a batch of very expensive corrosion inhibitor strikes me as a good way to spend a bunch of money and develop a difficult disposal problem without adding any value at all.

I can live with (and even sometimes recommend) corrosion inhibitor in lines designed to be liquid-full in normal operations. I strongly resist ever adding it to a line that is intended to be gas full because the transport of the chemicals is so hit-and-miss (mostly miss) that they accumulate in early low points and never get to the later ones.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Sam066]

Thanks zdas04 for your input,

How would you ideally deal with this situation knowing that the pipeline commissioning will take place from one to two years after the construction is completed?

Sam

 

[zdas04]

After I fired the project manager I'd most likely put thermal releifs on the high point vents (if there are any) and make sure that the line stayed liquid full of a benign mixture like water/methanol (which is pretty toxic stuff for people, but fine for pipe) or water/glycol mixtures.

Emptying it, running a series of drying pigs, batchiing corrosion inhibitor, shut in full of air for a couple of years sounds to me like a recipe from MacBeth to mix up a cauldron of serious trouble. If I found a pipe in that condition I'd run another pig with nitrogen and leave the system with 3-5 psig of nitrogen pressure. Just make damn sure that the nitrogen-fill process includes prohibitions against injecting it below 60F (the gas not the pipe or ambient). Bulk nitrogen is really really cold and if the truck driver isn't told to keep the temp up then he'll tend to pump as fast as he can. There have been a couple of recent fatalities from the brittle failure that resulted, in neither case had the design engineer specified the injection temperature.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Sam066]

Re-thanks.

One more question though. What would you fire the PM?

Sam

 

[zdas04]

Big inch pipelines represent a significant capital investment that has a finite shelf life. Finishing the pipe a couple of years before it is ready to be used may be supportable, but a project schedule should be able to orchestrate completion dates closer than that.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

Big waste of permaturely spent capex plus a lot of construction period interest cost.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[MortenA]

Wrt to the anti microbial effects i dont think you have to go as high as 50% Im a little rusty, but i believe that its a lot lower.

 

[stanweld]

If this is a long cross country pipeline, completion could take considerable time. Hydrostatic testing would be done in increments (sized to meet water availability and disposal. After testing, the water is removed by the use of pigs; a slug (or slugs) of methanol is used to effect drying, and full water removal.

 

[SJones]

Th OP suggests that the hydrotest medium is a water/methanol mixture rather than the resulting mixture from a methanol swabbing operation. In a duplicate thread, the OP's concern seems to be the quality of the final drying. That concern should be addressed by setting drying criteria in a pre-commissioning specification, and then obtaining objective evidence that the criteria have been met.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.