I am in process of evaluating relief header for one of our unit. From plant operations it is known that this header is also used as dump header. They tell me that this 1100 ft of 12" has water contained in it all the time.

Now from reading API it looks like having water in your relief header all the time is not a good practice as in the case of multiple relief in vessels attached to this header there will be lot of back pressure due to water in the relief header and also this might create two phase scenario in header.

Some of the header piping is under ground so we do not know it's capacity to expand and suspect that entire length of pipe will cause undue stress and a high liklihood of failure under relieving conditions.

I want to know what approach should i take to evaluate this header. Is there any specific way to evaluate header with wate in it all the time??

Thanks,

AJ

AJ,
I think in the first place, the information provided is insufficient to provide further advice.

You mentioned that the header is used as dump header. What is the meaning of this statement ? Is it drain header ?

When you said the header has water contained in it all the time, what does it mean ? Is it a low pocket ? Is it the header outlet is submerge in a seal drum ?

Is there any KO drum in your system ?

Is the header slopping in to the KOD ?

Please submit some sketch for better understanding.

The way you present your information, sound that you are not 100% understand the situation. This is very dangerous. Rubbish in rubbish out. The advice that you get may total useless as the information provided is not true. Please check and verify your situation and information before you ask for advice.

If you are indeed going to evaluate an existing PSV relief header, then I highly recommend you first - before doing anything else - take an AS-BUILT listing of ALL the relief devices relieving into the header AND an AS-BUILT P&ID of the header system and perform an accurate and detailed check on all the capacities and their combined flow rates. I cannot over-stress that the listing and the P&ID be AS-BUILT. Confirm everything on the P&ID - especially the PSV rated capacities. You will never regret doing this essential, up-front work detail.

If you fail to do the above, you are leaving yourself and your design check at risk if the header design winds up being modified or not documented - or both. After many years of finding mistakes, oversights, and the wrong installed equipment out in the field, I would not be surprised if you find you are working with the wrong basic data in your evaluation.

In order to accept and respect all your evaluation work results, the accuracy of the basic data must be confirmed.

Good Luck.

Joe,

I accept everything you said. And I understand that half-information is bad for evaluations. But I am still trying to find out lots of information as Mr. Montemayor suggested. And he is right; I am getting so many conflicting details.

Now let me explain few things (based on information i have at this time, and I am still trying to get more information):

By sayind dump header I am implying that this header system is used at times as a drain header. And yes, there are low pockets in the system. In fact, there is a total 1,100 ft of pipe and 75% of it is under ground - and at the end of the system there is KO drum too.

I am still in the process of tracing complete line and all assoociated PSV on as-bulit P&ID's.

I want to know your take on the header system which is underground, and also has pockets of water in it. This is first time I have dealt with this type of system. I will try to post more information once I have it -- Mainly sketches.

Thank you for your time.

AJ

PS: Joe, I know that this is not enough information for any one to comment anything on, but I just wanted to give whatever information was availabe to me at this point.

Josh:

You are doing the right thing. And what is more important, you are doing it with the right attitude. Do not put your faith or trust on anyone's word or hearsay. Demand and obtain DOCUMENTATION and calculations on ALL the related equipment - PSVs and the header(s). As I said previously, do not be surprised (or perturbed) upon finding discrepancies – and errors – in the existing installation. This is the purpose of doing a header evaluation. That’s why they have you out there and why they are relying on you to confirm that they are operating safely. Don’t let anyone down by being lax in your analysis.

“Walking down” the As-Built P&ID and personally confirming what is physically out there is the smartest thing you can do. Items such as the size, location, and length of the PSV inlet and discharge nozzles should be checked. Do not be surprised if some PSVs are in violation of the 5% inlet pressure drop API guideline. Make sure that the indicated PSVs on the P&IDs are, indeed, there – and that they are the correct, specified type and capacity. If you are doing this for CDI or as a CDI rep for a client, do not accept the claim that “strict Management of Change” has been practiced and that the system is totally as depicted on the P&IDs – at least not without a written and signed statement to that effect. That is why personally walking down the P&IDs is the best insurance – for everyone. Your evaluation will rest on the Basic Data that is on the P&IDs and installed out there in the yard. You have to protect your client and yourself and verifying all the basic data is part of that job.

You are on the correct path in challenging the type of header, the type of fluids deposited there, and how it is operated. Too many things can go wrong with an underground header if the design and the operating procedures are not checked and followed religiously. You have a tough job on your hands, but base your decisions on facts, logic, safe operating practices, and good engineering judgment.

Good Luck!

Josh,

Good...

My experiences tell me that you spent 50% of your time to find information, 30% of your time to validate the information and remaining 20% of your time actually doing the real work.

The percentage is just arbitrary figures. It tells you that correct information is vital prior to inception of any works.