Scope - Tank Vent Piping/Ducting

[1974vet]

What code applies to the piping/ducting that is connected from a tank nozzle to an emergency vent/conservation vent? For this example, a tank built to API-610 is located indoors, and the piping/ducting essentially routes up throught the roof to the emergency and conservation vents. B31.3 appears to exculde this piping in 300.1.3. It seems that given the low pressures, thin wall stainless tubing or piping with plate flanges (say 1/4 or 3/8) will work fine. And due to the low pressures, the rules for unlisted components (B31.3) seems excessive. Also, SMACNA does not seem appropriate from what I have seen, as leaks in some of the ductwork are allowed. The client wants to save money and use thin wall stainless and plate flanges, but I'm just not sure what code applies. Any help is appreciated.

 

[1974vet]

API-610 = API-650
sorry

 

[JoeTank]

API-650 does not address this issue.
API-2000 might, but I do not have a copy to check.
NFPA-30 might, but I don't have a copy of it either.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[1974vet]

Steve,
Agreed, API-2000 does not address this issue, but NFPA 30 does. The following are excerpts:

"3.2.1 Performance Standards.
The design, fabrication, assembly, test, and inspection of piping systems shall be suitable for the expected working pressures and structural stresses. Compliance with applicable sections of ASME B31, Code for Pressure Piping, and the provisions of this chapter shall be considered prima facie evidence of compliance with the foregoing provisions.
3.2.2 Tightness of Piping.
Piping systems shall be maintained liquidtight. A piping system that has leaks that constitute a hazard shall be emptied of liquid or repaired in a manner acceptable to the authority having jurisdiction."

One way to interpret this takes one back to para. 304.7.2 (using B31.3) for unlisted components, like plate flanges. This paragraph requires (a) "armwaving" (I'm not gonna do) or, (b), (c), (d), (e), techniques not at my disposal. The requirements of this paragraph do not seem excessive for high pressure or hazardous fluid transport. Anyway this seems to be somewhat of a circular reference given the defined scope of B31.3. The authority having jurisdiction wants plate flanges, and they do not have "standards", per se, for this application.

Lap joint flanges for an 8" vent pipe weigh almost 77 lbs each, where plate flanges will be significantly less. It just seems that if plate flanges are good enough for a tank manway, they should be good enough for the vent. If this is true, how do I get to there in the codes? Thanks. . .