Dry Gas

[sw71im]

Dear All,

The company I work for operates a dry gas pipeline, I was just wondering can we inject the pipeline with corrosion inhibitor to control corrosion (If any) and how can we monitor the corrosion, please note that pigging is not an option.

Your help is much appreciated

 

[EdStainless]

There is no corrosion in a dry gas line.
Unless someone messed up and let it get wet.
Filming inhibitors will coat the inside of the pipe and protect against the occasional moisture exposure.

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Plymouth Tube

 

[brimmer]

Yes, you can use continuous injection to inject an inhibitor, any reputable chemical provider will have something. You can install corrosion coupons, or other devices such as ER or LPR probes to monitor. The same principles apply as if it were wet gas. If truly dry all the time, you will not get corrosion. I don't know your scenario, is there a dehy? You can also monitor the dehy to ensure no wet gas get delivered into the line, can also monitor dew point, will the temp of the gas ever reach the dew point? Then you will have free water.

 

[zdas04]

The question you have to ask yourself is "how will this chemical be distributed?". All of the pipeline chemicals that I know of are intended to be transported in a continuous phase liquid. Gas just doesn't have the mass to transport much liquid very far.

With aerosol injection, the collisions of the droplets with other droplets and/or with the pipe walls will end up with zero buoyant droplets within a few dozen feet. When I've cut open pipe with aerosol injection, I never find any chemical after the first or second sag in the pipe. Aerosol injection is worse than worthless.

Liquid injection is just as bad, but less expensive.

Batching chemical behind a pig can work, but getting the batch size right (i.e., put in enough that there is still some left when the pigs arrive) can be a challenge and I usually see the pigs arrive stone dry and no one knows how far the line is protected.

I have never seen a "protected" line with a lower failure incidence rate than a line in similar service without chemical injection. Never. Not once.

I have also never seen a corrosion failure in lines that are regularly pigged. Getting rid of the water is the only effective corrosion treatment that I've ever seen in "dry gas" lines (the term "dry gas" in my industry means "gas without hydrocarbon liquids", I've never seen a line with zero water in it--even dehydrated mainline pipes will accumulate some amount of water in cold places).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[strider6]

if it's "dry gas" corrosion can occur only during upset or shutdown of the line. "Dry Gas" is considered a gas that has a water dew point at the actual pressure at least 10°C lower than the actual operation temperature (Norsok M001)

http://www.sveis.no/dok/tekniskestandarder/M-001_0.pdf

for "dry gas" service corrosion allowance is not specified or a minimum, say 1 mm, is used.

The only reason to inject inhibitor is if you want to continue operation even if the dehydration is not working nad you'll have water in the pipeline.

http://web.nace.org/departments/store/product.aspx?id=3319b11d-76f6-4620-b76a-64d028dc4e37

S

Corrosion & Rust Prevention Control

 

[sw71im]

Thank you to everyone who responded, Your input was much appreciated

 

[zdas04]

Strider6,
Your definition of "dry gas" is not the one that I find used in the industry over most of the world. I looked at the link you provided and that definition is not there either. In fact the only time the phrase "dry gas" is used in the Norsk document is in conjunction with the corrosion allowance discussion.

In general usage, "dry gas" is gas without liquid hydrocarbons. I find that usage in every country that I work in. The term has nothing to do with water at all in my experience. When a stream is anticipated to be free of water, the term "free of water" is explicitly defined, usually in terms of a mass of water per volume of gas since the industry has long known that it is very expensive an generally pointless to get the stream to approach zero water vapor.

David

David

 

[SJones]

Unfortunately David, you are now having to speak 'corrosion'. Corrosion people are generally only concerned about the water, and to them "dry gas" is gas with no risk of water condensation.

PS. You need to look at the second paragraph of 4.3.2 in NORSOK M-001 (under the bullet points)

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

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

 

[zdas04]

I see it now. Thanks for pointing it out. I did a search on "dry gas" not "the gas is considered dry". My mistake.

The OP was talking about injecting chemicals into a "dry gas" pipeline. People do this a lot. It never provides better corrosion performance than not injecting the chemicals. That seems more important than a pedantic definition.

David

 

[SJones]

But one must question the need for the CAPEX, and substantial OPEX, of injecting chemicals into a pipeline system that doesn't require them for corrosion control.

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

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

 

[zdas04]

I always do. I've taken over responsibility on 6 different pipelines in my career. Every one of them had chemical injection when I took them over. I cancelled the contracts in the first month. I implemented pigging schedules in the second month, and in every case corrosion incidents went down.

Since I retired I've looked at several dozen dry gas lines around the world for many operators that have chemical injection (either aerosol or liquid, it doesn't matter) and had them sample the liquid that always comes out when you cut the line. If the cut is close to the injection point, the liquid is nearly pure chemical. If it is more than a couple of dozen joints downstream there is no chemical in the liquid.

Neither the CAPEX or the OPEX (or the manpower) is justified in slathering corrosion chemicals into a gas line.

David