Nitrogen Purging to Prevent Internal Oxidation

your firm needs to hire a qualified Jr engineer

"but no additional specification has been requested"...and that's where the problem is. Before accepting a contract, all of these questions you have should be specified!

1) What is the level specified in the contract?

2) What is the code, or requirement specified in the contract?

3) The method specified in the contract, or by the code or requirement specified in the contract.

As stated, If your company has no one on staff who even knows where to look for these answers, they should retain a competent pipeline consulting company or quit the job entirely.

Google "pipeline construction".

Pipeline Safety - eCFR - Code of Federal Regulations

OP could just fill the pipeline with water.

I'm not in agreement with you on this one. I think he does need better communication and clarification of his contractual obligation but I think the vacuuming is unnecessary and costly. if the contract calls for purging and sealing why not meet those specs?

I'm just using my background and experience with recommending a vacuum pump down purge. Pumping down to 1/Y of an atmosphere of pressure provides a metric for completing a process while confirming a reasonably sealed system. The problem, as I see it, is the lack of specificity in how one properly purges this line and demonstrating that a purge was performed properly. Just measuring the amount of gas pushed into a container tells me nothing unless I know the path this flow takes.

it should have been clearly laid out in the contract language......they have a deficiency there. I understand it as, "install a pipe, seal it, purge with nitrogen. seal again with 10 psi nitrogen." deliver to customer, contract Complete.

Not familiar enough with pipe lines but nitrogen purging is used in both the water well and oil well industries. Maybe this will help.

https://www.rigzone.com/training/insight.asp?insight_id=329&c_id=4

http://www.epa.gov/region1/lab/qa/pdfs/EQASOP-GW001.pdf

Nitrogen purging is not required. Your steel pipeline can be kept free of oxidation by maintaining the relative humidity below 50%.

the thing is there has been some development of mild internal oxidation which has resulted in the client requesting nitrogen purging. This is to stop further oxidation within the line.

A big Thanks to those of you replying without a lousy side of sarcasm. Lack of clarity in the contract is a valid issue here. Nitrogen purging has been mentioned only once in the contract in fine fonts and as a foot note to one of the clauses regarding the quality of pipeline. The principal issue wiv contacting the client for instruction is their lack of sufficient in-house knowledge regarding the matter. Additionally, internal rusting of the steel is rarely ever an issue in the area (meaning that the client itself is not aware of the technicality of nitrogen purging as a mean to stop oxidation.) Therefore, requesting for instruction would result in them asking for 100% concentration of nitrogen within the network without any knowledge behind it. Thereby we are trying to gather a feasible method based on (any) codes of practice or standards since none has been specified in the contract. The biggest difficulty for any negotiation here is the fact that this is a traditional type of procurement. So the proposed design has been paid for long before we accepted the contract.

Then you should be asking your Contact Manager rather than some bunch of Muppets on the internet.

Nitrogen, actually, is the cheapest bulk gas available that hasn't got any water in it, and that is why it is used. Do check that the line has been tested hydraulically to a higher pressure before introducing gas under a lower pressure.

It seems that your client is not the only entity with a lack of sufficient in-house knowledge regarding the matter.

Your post makes no sense at all. A utility who owns and runs a 24 inch gas mains and stipulates a pressure of 10psi in a contract has issued you with standards and spec to test and commission this line.

There are many specs for purging pipelines as these pipelines are used world wide by many companies in the gas business. Nitrogen is a common gas to use to expel air from packaging and pipelines.

What is the Typical method of procurement you mention? If the design is paid for upfront, who is doing the design now? No design is built to the original design as mods and variations are an ongoing process.

Your project manager and contract manager would have this info as it is written in the original tender docs, along with the standards to use. Any gas mains owner will have the info and standards for his 24 inch gas mains on record.

It looks to me that you are in ZA and if I am correct, you have plenty standards for gas mains and purging and if you are in Europe you should not be working on gas mains as the requirements for this would ensure you know what you are doing.

The whole post is nonsensical.

It is a fact that Nitrogen is extensively used for preventing oxidation in Pressure Vessels in Chemical Plant projects until the plant is erected and commissioned, as it takes a long period of idle time before the vessels are erected & commissioned.

If the Client wants Nitrogen purging of the pipeline, I believe it has to be filled and maintained under some positive pressure above atm. (need not necessarily be as high as 10 psig which is almost 1.7 bar). If the gas pipeline has to be kept without internal corrosion, there is no other way than to fill the full vol. of pipe with Nitrogen under +ve pressure to account for some leakage. You can only claim extra costs on the basis of lack of clarity in the contract regarding your scope.

No one knows what the client wants.

"Nitrogen purging has been mentioned only once in the contract in fine fonts and as a foot note to one of the clauses regarding the quality of pipeline" and no one has asked for clarification.

OP doesn't want the client to know that his company is"without knowledge" because he believes that, "requesting for instruction would result in them asking for 100% concentration of nitrogen within the network without any knowledge behind it."

The pipeline is already rusted, so purging will arrest further oxidation, but not insure the quality of the pipeline, which will be determined by the client.

10 pound per square inch (psi) = 0.68 Bar.

You are right. Actually, I meant 1.7 bara considering atm. pr. as 1 bara.

Thanks.

Not a problem. BarA being absolute pressure and BarG being gauge pressure of course.

However, purging with nitrogen would not quite help at 10psi.

HI ZA

Is similar to that used for long term storage

Preservation after pre-commissioning has to be discussed separately with the client.

The end of guarantee from vendors is to be considered since the requirements in this procedure relate to prolonged storage of material (expected duration of storage 1 year or more).

Specific preservation requirements of vendors will be followed as far as possible. If there is a conflict between manufacturer's recommendation and the recommendation in this procedure, the vendor's recommendation shall take precedence.

The extent of preservation will depend on the anticipated period that the equipment is to be preserved. This is to be handled in close conjunction with the client's representative and the vendor.

Rust preventatives and desiccants are sold under various brand names and have to be field purchased as required. Before purchasing starts, agreement has to be reached between field and client on brands and types of rust preventatives and desiccants.

• 1.-Systems containing hydrocarbon will be sprayed, flushed or filled with a suitable oil or inert powders..

· 2.- Nitrogen blankets will be applied and maintained on stainless equipment.

Apply nitrogen blankets preferably after all internal work is finished in order to avoid extensive purging operations. Nitrogen in a vessel can be dangerous. Apply all necessary warning plates near all vessel entrances.

All construction personnel shall be familiarized with the risks of nitrogen blankets. This instruction is the personal responsibility of the safety engineer.

Austenitic stainless steel items can be internally protected in accordance with the following preservation method:

· Shop installed gaskets and blind flanges shall remain un removed until installation of piping.

· Maintenance of a nitrogen blanket on austenitic stainless steel is imperative.

· The nitrogen gas pressure in the equipment shall be checked regularly.

· If the pressure is below 0.5 bar(g), a refill with dry nitrogen is required. The oxygen content shall be less than 2 % by volume measured at the flushing outlet which shall be a maximum distance from the flushing inlet. The refill shall not start before nitrogen pressure is at 0.1 bar(g). When a pressure of less than 0.5 bar(g) is recorded, close monitoring is required (at least one a week).

· When depressurizing is required during erection of equipment, it is imperative that the nitrogen blanket immediately be restored when this action is completed. Equipment shall be absolutely dry before refill can start. Temporary covers to avoid ingress of water are mandatory.

· If the equipment is to re inspected, safety precautions are to be taken. Refer to Project Site Safety Procedures.

WP

As others have stated, both the potential customer, yourself and perhaps others in your firm need some remedial training on the fabrication, start-up and operation of gas pipe lines.

First, never pull a vacuum on a pipeline that will be used for pressure purposes. It wasn't designed for that and could possibly collapse part of the piping. It is much easier to collapse a pipe with a vacuum within it than it is to burst it with internal pressure.

If they insist on nitrogen purging consider the use of Dewar flasks of liquid nitrogen with an appropriate heat exchanger (similar to an automobile radiator). If you need more than those get a bulk trailer of liquid nitrogen and purge the pipe with the vapor from it. Cylinders would be very costly for the volume you are using. 2,800 m³ is a lot of anything. Estimate needing at least 5X the pipe volume for the gaseous nitrogen needed if direct purging is done.

In the USA the normal start-up for a new or extensively repaired gas pipe line is to have personnel enter the piping to clean out any garbage. Next flush the pipe with water to remove any materials within it. Close off all valves, etc., bleed off any air at the highest points, bring the pressure up to test pressure and disconnect the water supply. Wait for no drop in pressure. If pressure is not stable find the leak, repair it and start over again. For 24" to 42" pipe lines running at 1,000psi the test pressure is at least 1,200psi or the design test pressure.

After the test pressure has been held for the specified time: release the internal pressure, pump out the water, remove any line blocks (balloons), pump out all low spots and then pig the line to remove all water. This will take several to many runs of various pigs to clean it out and dry it.

Instead of purging the line with nitrogen directly I would suggest having the last pig run propelled by using a sealed rim pig and pressurize the line behind it with nitrogen to propel it. The nitrogen will replace the potentially moisture laden air with an inert atmosphere, the pigs will clean the interior of the piping and the pressure increased to the desired pressure, 10 psi. The pig can be removed at an appropriate removal point past the end of the pipe.

If you find it necessary to test the interior for rust or other materials a "cleaning pig" can be run through the line to remove and collect the materials. At any time another pig which checks for anomalies in the piping can be run and a report developed.

THIS IS NOT A PROCEDURE FOR COMPLETE PURGING OF A PIPE LINE WITH NITROGEN! It is only an overview of what can be done along with your consultant and codes. You and the customer are the ones that have responsibility for the pipe line, I don't. Get the necessary information and calculations from a very smart, and probably expensive, consultant with extensive experience with pipe lines.

Good Luck, Old Salt