ASME/API Fire Analysis

[DonyWane]

What are the requirements for evaluating the pressurization effects of external fire on atmospheric vessels? If there is no credible fuel source (ignition source is present, but no fuel), is it required by Section 8 of ASME BPV code to ensure the atmospheric vented vessels would remain below 15 psig in the case of fire? If you could offer suggestions and/or point me directly to the resolution to my question in the code, I would be most helpful. It seems rather ridiculous to analyze for fire if no fuel source is around (filling/draining and pressure control valve failure are already being considered).

Thanks!

 

[pleckner]

First, atmospheric vessels do not fall under ASME Section VIII, Division 1. They fall under NFPA and API 2000.

Second, there is nothing that says you have to size an emergency vent or relief device for a fire scenario if one does not exist. You just have to document for the authorities that you looked at it. If your conclusion is that fire is not a credible scenario, so be it. It's the same as if control valve failure was not credible. You wouldn't size a relief device for that scenario if it was not credible, would you?

 

[pleckner]

Add API 650 to the list of Codes as well.

 

[DonyWane]

Although I do not know the details, we have determined that NFPA is not applicable to our situation. Since I don't know the details, I can't elaborate...but assuming that is correct...what actual code drives atmospheric vessels in this case? Previous versions of API are not actually code, is that correct? However, I know that API 2000 is listed as an actual standard. I suppose my question is that API can serve as our car to get us where we are going....but what serves as the driver that determines where we are going?

Thanks!

 

[EGT01]

Watch out for questions like that last one, you might get blind-sided.

Not trying to be mean but in case you aren't aware, YOU are the driver. Only you can assess your problem and determine where you are going. Hopefully, it is to a safe place. If you are uncomfortable with making the drive alone, request the assistance of fellow co-workers such as might be done during a Process Hazard Analysis (HAZOP, etc) or retain a consultant to do the work.

I agree with pleckner's comments and you seem to have the same idea about discounting fire as being unlikely but you seem unsure about it because you can't find it in a code.

Generally, the codes, standards or practices are not going to tell you what the hazards are in you system, you have to determine that yourself. Though language such as that in NFPA 30 helps to assess the hazards. Similar guidance can be found in API Recommended Practice 521 but that usually applies to pressure vessels. You may also want to check some of the AIChE publications for process safety or relief system design. OSHA 1910.106 covers flammable and combustible liquids but I think it is more a compilation of the earlier established codes, standards and practices.

It will be important to establish to which standard or code that your equipment was constructed. That info certainly will be needed in sizing your relief or vent system to allowable criteria (vessel pressure accumulation) no matter what the overpressure case is. What kind of vessel is it? Flat bottom vertical storage tank with a fixed roof, horizontal cylinder with dished heads? Fabricated from steel, fiberglass (RTP), other?

Just for info, here are a couple of excerpts that may help to ease your mind. Though it sounds like ASME Sec VIII wouldn't apply, from UG-125 (c)(2) Where an additional hazard can be created by exposure of a pressure vessel to fire ...
Obviously, if there is no chance for a fire, you can't create a hazard. In other words, you can't evaluate the pressurization effects of a fire if you can't have a fire.

NFPA 30 Flammable and Combustible Liquids Code
2.2.5.2 Emergency Relief Venting for Fire Exposure for Aboveground Tanks.
Exception: Tanks storing Class IIIB liquids that are larger than 285 bbl (45,306 L) capacity and are not within the diked area or the drainage path of tanks storing Class I or Class II liquids do not need to meet this requirement.

Though you say NFPA doesn't apply, I would point out that the emergency venting tables in API 2000 are based on NFPA documents. NFPA are well established guidelines for fire protection issues. Even if you are dealing with a storage tank for acid or caustic, it is not unusual to spec an API tank in which you would follow API 2000 for venting requirements. If your vessel contains water you may want to look at some of the AWWA standards (D100) to see if anything there would apply.

 

[DonyWane]

Thank you EGT01. I will look at some of the sources you provided. And...no...you weren't being mean. I understand what you mean by me being the driver, and don't disagree. I guess, in that case, my question should have been "What should I use as my drivers manual?" Basically, most things we do are driven by code..or basic guidance is provided by code. My confusion was that if I have been told not to look at NFPA and if ASME Section VIII doesn't apply...what is the code I need to look at. In the cases I am considering, I am looking at storage of water, caustic, etc. Your guidance was helpful...thanks!

Wayne

 

[pleckner]

EGT01 said it very well. But let me repeat, atmospheric tanks do not fall under the scope of ASME Section VIII, Division 1. They DO fall under API 650 and API 2000. I really haven't read OSHA 1919 thoroughly enough (one day) but you should see if there are relevant paragraphs for you. Only you can decide whether they are relevant to you, we cannot nor should we.

If your tank containing non-flamable liquid is not within a fire zone (within a 50 ft. diameter of another source of a fire), then you don't have a fire scenario to be concerned about. I guess you were told that NFPA isn't applicable because flamable liquids are not the concern. Well, so be it. However, API 650 tanks have to be designed to API 650 standards. You will note that this is called API 650, NOT API RPxxx. The "RP" stands for "Recommended Practices". API 650 is NOT a recommended practice, neither is API 2000 (unlike 520 and 521 which ARE). You must conform to them for these types of vessels.

We can't emphasize too much that you do not need to make up hazards. I'm sure you can find plenty "real" ones!