tank emergency venting requirement

[vesselguy]

Hi all,

Pardon me with this trivial question but I'm working away from my office and have no access to reference material and I need a quick answer. I hope someone can help out here.

I just need a confirmation if I need a tank emergency relief valve on a storage tank (APi650)with frangible roof joint. I know API2000 section 4.3 specified this is optional but I think I recall NFPA 30 forces us to still put one on (or several depending on capacity) for fire case. Can someone with access to NFPA 30 or expert knowledge on tank venting confirm this for me? Thanks for reading this.

 

[JoeTank]

I too am away from the office, but do not recall any NFPA requirement that mandates a pressure relief device if the tank has a frangible roof.

Joe Tank

 

[doct9960]

vesselguy,

See page 30-14 on this document...

http://www.nfpa.org/assets/files/PDF/ROP/30-F2006-ROP.pdf

Chapter 22.6 on the above document corresponds to Chapter 22.7 of the 2008 Edition of NFPA 30.

As I understand it, a frangible roof joint is considered an "emergency relief venting construction".

 

[vesselguy]

Joetank, Thanks for responding.

Doct9960, Yes, I am aware that the frangible joint is considered an emergency relief "device". That's why I mentioned API2000 give us the option to put on an ERV when the roof in frangible. What I'm not sure of is what NFPA 30 dictates us to do. I remembered I read long time ago that NFPA 30 insists on a ERV for fire case even if the roof is frangible, but I'm not sure since its been 10 years ago. Heck of a time to forget to bring along my repository of knowledge in my portable drive.

Thanks guys and good night.

 

[CMA010]

Just browsed through NFPA 30, but it does not dictate an ERV for a tank with a frangible roof connection (NFPA 30, par. 2.2.5.2.2)

 

[doct9960]

vesselguy,

API STD 2000 paragraph 4.3.3.1 gives you the option to add emergency vents on frangible roof joints. The purpose of those nonmandatory vents is to avoid failure of the "frangible" joint.

 

[MJCronin]

Uuuummm...

My two cents....

As a mater of practicality, I suggest that the emergency device always be installed and that the reliance on a "frangible roof joint" to meet code requirements be discouraged.

As we all know, the shell to bottom welded joint is the most highly stressed one in the tank and also in a location most prone to corrosion. Whether that corroded joint or the "frangible roof joint" would be first to fail in an accident is up to anyones guess.

A few years back, there were seminars concerning the actual effectiveness of this type of roof joint on smaller diameter tanks.

The preferred device, as I understand, is always the manway mounted spring relief device. You do, of course, need a roof mounted manway.

My recollections only....

-MJC

 

[IFRs]

API 650 11th Edition Addendum 1 has an entire section devoted to frangible joints - 5.10.2.6 which bears reading.

 

[vesselguy]

I've done my damage and this is done. I had specified that we put on ERV along with the fragible roof joint simply for practical operation purpose: That is, to minimize fixing crack roof joint. Yes, fragible roof joint is not to be used on small tanks of say 30ft and smaller. Thanks all for your responses. Over and out.