Volume based exemption for pressure vessels?

[SM2K]

Hi,

Is there any code or guideline which exempts a vessel from having a relief valve sized for a fire case based on volume? I have seen specific companies having a guideline to exempt a vessel from fire case if the volumes contained were less than 15-60 gal. I have searched through all I could find but didn't find a specific mention in API 521 or ASME. The vessel in question is a filter, and it does have a thermal valve on it.

I would appreciate if anyone can guide me to the right code or guideline.

Thanks,

SM

 

[jcfoley]

SM2K,

What fluid is in the filter? Is the filter subject to a fire hazard? Are you the manufacturer or the user? These questions are rhetorical - see below.

There are exemptions to vessels containing water in the 2004 ASME Section VIII code. This section on scope (U-1) was modified heavily either with this edition or the one just prior to it. The exceptions apply only to water heated by indirect means. The volume limit was 120 gallons but several temperature and pressure limits also apply. This could exempt vessel from having to follow ASME simply by the scope of the code.

ASME Section VIII does place the responsibility of PRVs on the owner, NOT the manufacturer. However, I have just made a fire scenario review of Section VIII for my applications. The code says something like "where an additional hazard can be created by fire" or something like that. It is not very specific about the fire risk other than to require fire size PRVs.

I have seen no reference on "exempting" a vessel from fire sized PRVs. However, good engineering practice should prevail.

Chris Foley
Midland, TX

 

[EGT01]

SM2K,

I have also known some companies to use the language in ASME Section VIII, Div 1, paragraph U-1(c)(2) as "part" of the argument that they did not have to follow ASME code regarding pressure relief for fire exposure. That paragraph lists certain classes of vessels considered not within the scope of the division but code be stamped with a Code U symbol.

But the other part of the argument would be the "vessel" would have to be made out of piping components and could otherwise be classified as part of the piping system. In that case, you usually don't see piping systems that include relief systems to cover a fire event. I've heard that ASME B31.3 says something to this effect but all I can find in B31.3 is that only high pressure piping (2500# class or greater) actually discusses overpressure protection due to fire exposure (see K322.6).

As added reference, from the AICHE/CCPS publication, Guidelines for Pressure Relief and Effluent Handling Systems, in the section covering Fire Exposure...
"Piping: Typically relieve through connected associated vessels. Long or blocked-in sections of piping may require additional relief. Design decisions must be left to experienced designers."

If it is a filter that is always in service with another vessel, you may could take credit for the other vessel's relief valve if you were assured of an open path. If it is a dual filter arrangement with an off-line spare, that could cause complications for the one off-line unless you had a procedure to immediately drain the one taken off-line.

 

[jcfoley]

EGT01,

Well said. I should have mentioned the piping components issue in original post!

This question does lead me to ask another question however. If fire size relief valves are required, what heat input would you use? I have seen one chart in a code or reccomended practice but I cannot seem to locate it the second time around. Does anyone know of a good fire based heat input reference?

Chris Foley
Midland, TX

 

[SM2K]

Thanks jcfoley and EGT01 for your valuable inputs. I also remembered something which said that if the volume is below a certain number of gallons, it can be considered as a part of piping and hence won't require a fire protection. Well I think as jcfoley said they may have taken it out during the modifications in the recent issues.

SM

 

[EGT01]

JCFoley,

The heat input methods that I'm familiar with originate from either NFPA 30, API Standard 2000 or API Recommended Practice 521. Generally speaking, the NFPA 30 and API 2000 methods are applied to storage tanks while the API RP-521 method applies to process vessels but I have seen variations on applying these methods. If you are remembering a chart, it is likely the one in NFPA 30 or API 2000 which happens to be the same as the one in 29 CFR 1910.106

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9752