Placement of RVs on Piping - fire case

[Bill3752]

I am evaluating several dozen relief valves that are protecting piping. Per earlier posts I surmise that I must provide for fire protection of the piping per ASME. That being said, the actual location is of interest.
For example, several of the valves protect piping at railcar loading stations. The material is feed through elevated piping (~15 feet), which then drops down to nearly ground level. The valves are currently in the horizontal run of piping at the loading area.
Is there a code which dictates that the valves should be placed in the elevated piping? Or am I allowed to keep the valves in their current, lower, area?

 

[don1980]

There are no overpressure protection requirements, ASME or other codes, that mandate fire protection for piping, or even for pressure vessels. In almost all codes, the user is responsible for making the scenario decisions. Pressure vessels and tanks are typically protected from fire exposure when flammables are present, but piping is not.

That said, there are always special cases in which piping needs to be protected from overpressure due to fire, but those are the exceptions.

Speaking globally, the only mandatory requirement for fire protection is a US requirement (OSHA 1910.106) that applies to storage tanks (operating pressure < 15 psig) which contain liquids with a flash point of 200F or less. Otherwise, the user is responsible for assessing the all potential causes for overpressure, and using good risk management judgment in determining which scenario(s) to consider for the final sizing. For guidance, refer to API 521.

 

[Bill3752]

Don, thanks for the response. We do realize that not all piping will be in fire zones. However, the logic we have applied is as follows: (a) With the consistent references to both piping and equipment in ASME, plus the reference in B31.3 regarding process piping, we are defaulting to protecting piping for fire cases just as we would equipment, assuming (b) there is a legitimate chance of a pooled fire being present.
Your comments indicate that one would use a less conservative approach for piping vs. equipment. Can you point me towards a specific code that I might apply? I certainly don't want to be overly conservative when it comes to the piping.
Thanks again for the feedback.

 

[don1980]

Yes, there's a fundamental difference between the overpressure protection rules and practices for piping as compared to pressure vessels. The code for piping is the one you cited, B31.3. Pressure vessels follow the rules in ASME Sec VIII and API 521. Relief devices are installed on pressure vessels by default, whereas they are installed on piping by exception. Relatively few pipe segments need a safety valve.

Safety valves on piping are needed when there's a risk of overpressure from causes such as valve failure/misalignment. Piping in liquid services also need to be protected from thermal expansion, but in most cases that done by inherently safe design or by administrative procedures. There are certain liquid services (ex:cold services, heat-tracing) that justify a relief valve. There might be some large liquid line that justify a fire sized safety valve, but that is very uncommon.

There's certainly a risk of fire at a loading station for flammable liquids, and if that occurs the load lines need to be shut off so they don't feed the fire. I would focus attention on that rather than on installing fire-sized safety valves on the piping.

 

[Chance17]

In my experience, safety valves at rail car stations
are installed to protect hoses - not pipe.

 

[dcasto]

above ground lines that be isolated are subject to overpressure due to solar thermal heat. I use a small check valve that goes around the isolation valve instead of a PSV

 

[Bill3752]

Thanks for the responses.
The root questions are (1) Is RV protection required for a fire, and (2) for a straight thermal case, is a certified valve required? I have attached a couple of highlighted pages from B31.3 for reference. Section 301.2.2 pretty much indicates that RV protection is needed; however, a fire case is not listed in (b).
Section 322.6.3 states that the valves must be designed per Section VIII. However, note that UG-129 - U-136 are not included; these sections pertain to valve capacity certification and stamping.
On a separate note, API 520 mentions that vessels and piping are covered.
Bottom line on the fire issue is that I have left myself quite confused. And I am not sure if a certified valve is required, especially for thermal protection.

 

[Bill3752]

I see that my attachment did not in fact attach. Section 301.2.2 states "(a) Provision shall be made to safely contain or relieve any pressure to which piping may be subjected...... (b) Sources of overpressure to be considered include ambient influences, pressure oscillations and surges, ...., and failure of control devices."

Section 322.6.3(a) states "Pressure relieving devices required by 301.2.2 shall be in accordance with BPV Code, Section VIII, UG-125(c), UG-126 through UG-128, and UG-132 through UG-136, exluding UG-135(e) and UG-136(c).

Hope this helps.