Hi guys. Well SOMEBODY IS CONFUSED, but I don't think its me. Its MAOP + 10 %.
pmover's quote of CFR 192.169 is exact.
In combination with p 169, see part 201, where the set pressure is specifically addressed and the allowed maximum condition is plainly stated.
Reading this immediately took me by surprize, as I have never limited PSV set pressures to MAOP. Based on many years working directly for and with a number of major USA gas companies, Northern Natural Gas, Enron, Transco, TransTexas, Texas Eastern, and working on many projects at engineering companies specializing in design of both gas and liquid pipelines for all types of gas pipeline transporters from gathering systems to city gates, none of which limited PSV settings to MAOP, I have to disagree with your interpretation.
Looking directly to the text of the gas pipeline regulation and noting the highlighted lines of paragraph 201, of Part 192.201, I think its obvious what pressure setting is applicable,
[/quote]
§ 192.201 Required capacity of pressure
relieving and limiting stations.
(a) Each pressure relief station or
pressure limiting station or group of
those stations installed to protect a
pipeline must have enough capacity,
and must be
set to operate, to insure the following:
(1) In a low pressure distribution system,
the pressure may not cause the
unsafe operation of any connected and
properly adjusted gas utilization equipment.
(2) In pipelines other than a low pressure
distribution system:
(i) If the maximum allowable operating
pressure is 60 p.s.i. (414 kPa) gage
or more,
the pressure may not exceed the maximum allowable operating pressure plus 10 percent, or the pressure that produces a hoop stress of 75 percent of SMYS, whichever is lower;
[/quote]
OK, so you may ask, to what pressure does "the pressure" refer? "My logic is as follows,
Well, it absolutely could not be MAOP, so it must be referring to either PSV set pressure, or it is saying that it is the pressure in the system during a relief event. In either of those 2 cases the end result is that the maximum pressure IS = MAOP + 10% and, if it refers to "set pressure", or "relief event pressure", is immaterial, as BOTH have values greater than MAOP. As such, settings for relief valves CAN be higher than MAOP.
What about that part "75 percent of SMYS", what then? See section 192.739. This is especially interesting here, since sub (b) specifically mentions "MAOP + 4%" is the "pressure limit". Again, not specifically limiting PSV setting to MAOP.
That interpretation is not contradicted by 192.169 Compressor stations: Pressure limiting devices.
(a) Each compressor station must have pressure relief or other suitable protective devices of sufficient capacity and sensitivity to ensure that the maximum allowable operating pressure of the station piping and equipment is not exceeded by more than 10 percent.
Now, even though CFRs are law, B31.8 could play a part in that law by reference, so checking the provisions of ASME B31.8, once again IMO the limit is MAOP + 10%. In Section 843.44 pressure Limiting Requirements in Compressor Stations, 441 shows,
Pressure relief or other suitable protective devices of sufficient capacity and sensitivity shall be installed and maintained to ensure that the maximum allowable operating pressure of the station piping and equipment is not exceeded by more than 10%
Here reading that carefully, one we note that actual PSV set pressure is not directly addressed and that all pressures are simply limited to MAOP+10%, and this does not contradict the interpretation above that a PSV setting could indeed be higher than MAOP, as long as MAOP + 10% is never exceeded, and that provision applies to compressor station factilities too.
Additionally,
It is usually contended that MAOP is possible to be exceeded during transient events, as under the definition of Maximum Operating Pressure found in B31.8 section 213, MOP is defined as the highest pressure under a "normal operating cycle". If relief events are not included in "normal operating" cycles, then MOP is allowed to be exceeded during relief events. What relief event could possibly be included in a "normal operating cycle", when relief valves are designed to protect against "overpressure" protection? IMO, it is impossible to include overpressure within the definition of "normal" operating pressures. The concept of exceeding MAOP for transient events defined under maximum time ranges is recognized in various international codes, such as DNV, and many major oil/gas company pipeline design guides as well. Under the time limit definitions, it is hard to categorize relief events as normal operations, as they are almost always short term events. B31.3 recognizes higher PSV set pressures than MAOP. B31.3 on which the US Army process piping guide is based recognizes relief valve discharge as transient effects. EM1110-1-4008 5 May 1999, see example in Chapter 3, where relief valve set pressure is 2780, but maximum allowed operating pressure is only 2650, that representing a 5% increase over MAOP.
None the less, and allowing for misinterpretations to become entrenched in hand me down company standards in some manner or another, I made an extensive search through Office of Pipeline Safety records to find out if this question has arisen before and I have found the following interpretation by the Acting Associate Director for Pipeline Safety Regulation,
The allowable override of 10 percent of the MAOP is included in the regulation
As this OP deals with the specific application of set pressures to pipelines, I was wondering what the opinion is for other applications and spent quite a number of hours searching the net and turned up with this. Apparently the same rather convincing logic can be found for set pressures above working pressure based on capacity for vessel design, which I share and at the least this proves I'm not alone in my opinion, and no matter how hard this evidence is, there are some die-hards that still maintain PSV settings maximums should be MAOP of the vessel. Read the article here, http:/
Well, don't know if I convinced you, but I'll stick with allowing PSV settings over MAOP when necessary. It appears to me that OPS has clarified it very well.
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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that
99% for pipeline companies)
