Piping Pre Commissioning Leak Test and Nitrogen Purging

[king92]

Hello Dear Professionals,

I got promotion as engineer of pre commissioning and commissioning. But after getting into this position only i got lot of doubts that i missed to ask my manager during the preparation of documents in the last project.

1. For the leak test during pre commissioning, how the test pressure value is selected (In my last project we did 90% of design pressure, so i have contacted with him. As per his information it was taken from API standard. But he didn't told me the API number so i couldn't find it.) If possible can you guys help me on this one.

2. Is there any standard is available for inerting or nitrogen purging acceptance criteria.

If you know about these things please let me know. It will be helpful for my career. Thanks in adavance to all dears.

 

[1503-44]

Test pressure is prescribed by design code. Which code are you using?

Purging is done, when necessary, after hydrotest.
When necessary depends on what type of facility you are designing, pipe material and how long it might be between construction and when the pipe will be used.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[king92]

We are using ASME code for designing in old project also same. But i don't know which API standard they took 90% of design pressure as test pressure.

Purging will be carried out after the completion of leak test. Right ? So i need for the acceptance criteria for purging such as oxygen content and dew point. For that which standard need to refer. If you know please suggest me.

 

[LittleInch]

First find the design basis for the project. Much of what you need to know is written in there.

Then find the pre commissioning and test plan or are you trying to write it with no information or guidance?

Is this piping or pipeline?

"ASME code" means as much as "API standard". I.e. nothing.

The piping spec often contains this information

Purging is usually based on some percent of oxygen, I think <5% is where you need to be but again this should be in the inerting specification (or are you writing this as well?)

Tell us a bit more about your roles and responsibilities and which other engineers are there on the project with you.

Often the client will have this all written down, especially if it is a major operator or design contractor. Do they not have their own requirements or specifications / scope of works that you are working to or is everyone making it up as they go along?

Apologies if this sounds a bit harsh, but get this wrong and people die. It might be you, but more likely the lowly operator who is there at the sharp end.

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

 

[king92]

Yes sir i am writing the procedure for leak test and inerting. There is no any project documents available. That's why i asked about if any API or ASME standard which covers this one will be helpful. Because when i asked my previous manager he told that he took it from API standard only.

Like you said oxygen content value is that taken from any standard or from your project sir. If from american standard That's what i need sir.

There is no any standards or specifications available here sir from owner end or from our side.

 

[LittleInch]

Kinsly,

Then who is reviewing or approving your documents?

To say "There is no any standards or specifications available here sir from owner end or from our side" and "There is no any project documents available." makes it impossible for you to do your job so I would write to whoever is your manager or client and tell them that.

There is no "API standard" that describes that as far as I know.
The API 5L line pipe specification calls for a mill test to 90# of yield, but that's not normally used for piping.

90% of DESIGN pressure is totally incorrect. The test pressure MUST be the highest pressure the pipe ever sees so less than design or MOP or MAOP is not testing the pipe to its required level. perjhpas he meant 90% of Yield? but for piping you normally go 1.5 times the lowest MOP or design pressure in the system.

The most common piping design code in the world for petrochem is ASME B 31.3. That uses 1.5 times MOP. But your local code may be different. Without knowing what design code you are working to is the first thing you need to know. Everything flows from there. if you can't find one, state in your procedure that you are using ASME B 31.3 and let who ever is approving your document correct it.

Inerting

Look at this

https://www.hse.gov.uk/comah/sragtech/techmeasinerting.htm

You need to know what fluid you are inerting from to calculate the required min oxygen levels

There are not standards for everything - sometimes you just need to know it or state what you are using and let others review and approve it.

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

 

[1503-44]

What fluid, oil/gas, hydrocarbons, refined products, chemicals? Water, CO2. All have different requirements
ASME B31.3
ASME B31.4
ASME B31.8
Many others.
API 1110
API 1110 Pressure Testing of Steel Pipelines for the Transportation of Gas, Petroleum Gas, Hazardous Liquids, Highly Volatile Liquids, or Carbon Dioxide

Pipelines

https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-D/part-195/subpart-E

Facilities

https://docs2.cer-rec.gc.ca/ll-eng/llisapi.dll/Open/2776208

What are you building?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Snickster]

In addition to the ASME B31 codes indicated above, if this is a pipeline on public land the installations and testing mustcomply with 49CFR 192.

I believe it correctly 90% of SMYS (specified minimum yield strength) or 1.5 design MAOP for testing pressure but need to look at the requirements of the govening Code.

Procedures for purging are developed by engineer or client specifications. Never seen an industry procedure but one may exist, I don't know. Attached is an old pipeline purging procedure of a pipeline operator. As you can see it is pretty detailed and complex. You should really have some experience in this to understand all of the requirements before proceeding.

I would read over the applicable B31 standard - B31.3 Plant Piping, B31.4 Liquid Transportation, B31.8 Gas Transmission, and 49CFR 192. Understand testing requirements. Also may be some industry standard has white paper detailing purge procedures such as ASME, API, AGA, etc. You can go to their website and see if they have any publications available.

 

[king92]

Dear collegues,

Let me clear it one time, so you will understand it clearly.
I am not asking about the leak test for pipeline or during construction phase such as hydrotest or pneumatic test.
The test will be conducted after completion of hydro/ pneumatic test by construction team and air blowing by pre commissioning team. after the reinstatement of these tests will be carried out general leak test by system wise inorder to check the integrity of the system to be into operation. for that test only i am requesting your knowledge over it.

For the purging, need clear details such as dew point and oxgen content how much need to be present as per the american standards.

Here we are conducting work for gas processing plant and sulfur recovery unit. so as you know both of them having high concentration of H2S. but we don't have any specifications from our side or client side. so i would like to follow as per the american standards if available. so if you guys know about this please let me know.

actually i have refered some documents such as
ASME B31.3 section 345.8.2(the test pressure shall be at least the lesser of 105
kPa (15 psi) or 25% of the design pressure.)
ASME PCC -2 section 501-6.3 Tightness test (A sensitive leak test per ASME B31.3 is the
preferred method for conducting a tightness test. The applied test pressure for vessels and piping
should not exceed 35% of the design pressure)

If you refer both are ASME standard and refering to as sensitive leak test but test pressure given on both of them are different. I don't know how comes both of the standards are referring to same but having different test values. Because of these cnfusions only i can't take one value for testing purpose. so i am seeking your help.

we are creating a gas facility not pipeline and it's a new one not we are doing modification or repairing. Purging is planned to carry out using nitrogen.

 

[Snickster]

I found the very brief old project spec for cleaning and drying of pipeline. Just a little information. I will see if I have anything else in my files tomorrow specifically for a gas plant.

 

[shvet]

2. Is there any standard is available for inerting or nitrogen purging acceptance criteria.

Standard applicable depends on a local code. What is the piping code? Describe your issue in details. Start with CEN/TR 15281, AGA's Purging Practice and Principles, NFPA 56, NFPA 69, IGE/SR/22.

 

[1503-44]

Test Pressure
As per ASME B31.3 Section 345.4.2 the hydrostatic test pressure at any point in a metallic piping system shall be as follows:

[latexpage]

(a) not less than 11⁄2 times the design pressure;
(b) for design temperature above the test temperature, the minimum test pressure shall be calculated by Eq.
(24), except that the value of ST/S shall not exceed 6.5:

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

The ASME PCC test pressure is a do not exceed limit.

The ASME B 31.3 are the lower of two numbers. There fore chose which one you will use and stick to it - Probably B 31.3 sensitive test.

AFAIK Dew point and Oxygen levels are not something contained in any code or standard as they very depending on local circumstances and requirements. E.g. The dew point you need for say an LNG plant is a lot lower than you would need for a Crude oil plant.

Unfortunately the wording is confusing all round. Leak test, Pressure test, Strength test, tightness test can all mean different things to different people (and different codes) as you can see so you always need to describe what you're doing and not rely on a headline title.

It sounds like you're picking up this plant from the construction team after the main pressure test / strength test (B31.3 calls it a "Leak test" which confuses things even more) and basically preparing the plant for full commissioning so you want to both do a final low pressure sensitive tightness test of the finished plant after all flanges tie ins etc have been completed and also purging the system ready for introduction of whatever fluids you are processing.

Shvet has given you some ecellent guidelines and if you can ask around and see if anyone can give you the procedures used by the likes of Shell, BP, Total etc.

I am very surprised your client / operator has no such standards anr procedures, but are you the operator?

I understand why you're looking for rules and codes, but in this industry you often need to determine these things yourselves and then review and modify the next time. I think you've been hung out to dry here by your managers, but you need to at least ask for similar procedures and then don't just blindly copy them, think about your specific requirments.



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

 

[GD2]

Kingsly A,
We understand you are newly onboarded to your new role and we are as confused as you are.
When you say I am working on a gas plant with H2S, I would assume you will be working with sour natural gas.
When you say the piping would have been hydrotested an dried, I would assume you are talking of a 'Tightness Test' during your commissioning activities.
Most of time you talk about 'tightness test' but in one place you talked about 'Purging'

Now let me try to clarify few things:
'Tightness Test; and 'Purging' are two different things and objectives are differently looked at.
For example: you will have a natural gas line and, therefore, you will need to isolate air mixing in the line due to risk of flammability. This can be done by purging an inert gas like Nitrogen at a positive pressure than ambient.
But when you talk about a 'Tightness Test, you will be guided by ASME B31.3/PCC-2 that will direct to ASME Sec V Article 10 Appendix 1. Nitrogen (inert)gas testing medium is allowed by this test but you can also use air.

Now let me clear you on whether ASME B31.3 or PCC-2 and the difference in Test pressures.
You need to follow ASME B31.3, the reason being that it has not been placed into service yet. Therefore,.... at least the lesser of 105kPa (15 psi) or 25% of the design pressure will apply.
If you are to do the same thing in your next turn around, then you will need to apply the rule of PCC-2.

The reason why different pressures is:
Even if both the documents are published by ASME, these had been written by different committee members. Each group can have their own opinions and therefore the variations.

By using nitrogen, I would say that you will achieve both the objectives but could be an expensive option. To avoid this expensive option and where you will have multiple piping systems on the gas plant, the cheaper option will be to:
Charge the dried hydrotested piping section with natural gas with a leading nitrogen slug displacing the air but I don't think you would like to buy this option given the fact that it will be now as good as working in a live plant with a sour natural gas where construction work/workers safety will be compromised.


GDD
Canada

 

[king92]

Hello dears, thanks for the info shared. But i didn't find the solution. Like i said i am working in a sour gas plant which need to be commissioned. so after completion of hydro/ pneumatic test by construction team. we will start air blowing when blowing and reinstatement of the removed instrument and piping items installed then will start gross leak test for the entire system at a time. after completion of successful leak test/ tightness test of the system, will start nitrogen purging to displace the air inside the pipes. i am asking about this, which standard i need to follow leak test and purging acceptable values.
because in our last project we had like this

For leak test, test pressure should be 90% of design pressure, duration will be 4 hours and allowable pressure drop is 0.2% per hour
For Purging, oxygen content is 4 Vol% and Dew Point is -40 C

I don't know how my manager was selected these values but when i asked him that time he only mentioned that he took it from API standard. also i refered Commissioning Execution general specification for Total. In that also test pressure for leak test during commissioning is mentioned as 90% of design pressure. so i checked the procedure to find out the reference dcuments but i failed because there is no mention about that. so it confirmed that some API standard is there for leak test during commissioning and purging using nitrogen. So if you know this standard please let me know. Because i have Russian standard and Indian Standard for these works but i don't have American standard. i would like to know these standards for future references

 

[1503-44]

What references does Total's specification cite?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Mr 44. Don't you know that TEPs are written on tablets of stone handed down by the (French) gods of design and cannot be questioned or challenged! They don't need any references. They ARE the reference.....

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

 

[LittleInch]

Kingsley,

All joking aside I sense you're getting frustrated with asking the same question and getting no answer.

The reason is that for this sort of operation, there are no firm rules and requirements written into the codes.

The fact your manager cannot tell you which out of hundreds of "API standards" he means tells me he doesn't actually know, but doesn't want to appear that way in front of you or others.

Sometimes, indeed many times, you need to make your own engineering judgement based on your own particular system.

We've given you lots of help here, but only YOU can decide what to do next.

You can decide to pump up the system with air or nitrogen to 90% of design pressure but this either takes a lot of time or costs a lot of money. or you can do the sensitive leak test outlined by B31.3 which is low pressure and then you examine each joint for bubbles using soapy type water.

As for dewpoint, again that is a process driven thing and dependant on how dry you need the system to be in preparation for the fluids entering. -10C is generally the minimum dewpoint to stop condensation on the inside, but lower than -40 might be required if the fluids really don't like water vapour.

Choosing the right pressure and right dewpoint for you is not always easy, but too conservative and it will costs lots of money and take a long time for no real benefit.

You are being placed in a position which you don't have the experience for and not being given much or any help so I feel for you, but in that case the best place to start is from what you or your manager did before because then he can't blame you for copying it.

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

 

[1503-44]

LittleInch, Oui monsieur. There are no citations. That is my point. You can do what you like.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

When people need to reach low dew points and there is a chance that there is still some residual water in the system they commonly purge with air that has been dehumified and then heated initially.
Once it looks like they have the water taken care of (by watching outlet DP) they switch over to nitrogen and watch DP and O2 to reach targets.
Unless someone can give you an actual reference you need to make some judgements.
In my limited experience doing this it sounds like your O2 is higher and your DP is lower than I have seen.

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P.E. Metallurgy, consulting work welcomed