Interpretation Response #PI-76-0112

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date: 09/02/1976

Company Name:

Individual Name:

Location State: AZ Country: US

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Response text:

September 2, 1976

Mr. H. R. Garabrant
Gas Utilities Safety Engineer
Utilities Division
Arizona Corporation Commission
2222 West Encanto Blvd., Suite 210
Phoenix, Arizona 85009

Dear Mr. Garabrant:

This responds to your letter dated June 23, 1976, which discusses overpressure protection of
petroleum gas systems, stating that the pressure in the storage tank exceeds 60 psig during summer,
and suggests a technical review and “rule changes to eliminate the use of relief valves on piped LP
gas systems except when used as a second overpressure device downstream of a monitor and working
regulator combination and as required on LP storage, tanks.”

The significance of your comment that LP tank pressure will exceed the specific value of 60 psig is
not readily apparent from the information presented. Further discussion, therefore, seems
appropriate solely for clarification and to avoid
any possibility of misinterpretation. Title 49 CFR Section 192.195 requires that pressure limiting
or relieving devices must be provided so that the maximum allowable operating pressure (MAOP) of a
pipeline will not be exceeded, and that a distribution system which is supplied from a source
having a higher pressure than the MAOP of the system must have properly designed pressure
regulation devices which can be activated in the event of some failure and will prevent
overpressuring.

The criteria for determining whether a requirement exists for a monitor, relief, automatic shut
off, or other arrangement for overpressure protection, thereby, is the MAOP of the pipeline and not
necessarily a system pressure in excess of 60 psig.

A maximum actual operating pressure of 60 psig for a distribution system is applicable as criteria
only in connection with service regulator requirements. As set forth in 49 CFR Section 192.197,
pressure limiting or relief devices are required in addition to the service regulator if system
pressure exceeds 60 psig, but for distribution pressures below 60 psig, no pressure limiting device
is required other than a service regulator having certain characteristics.

On the basis of the described criteria, it must be assumed that 60 psig is significant either
because the MAOP of the referenced systems is 60 psig or that the services are not equipped with
pressure limiting or relief devices.

Regarding your suggestion that Federal regulations be changed with respect to the use of relief
valves on petroleum gas systems, a review by this office has concluded that the initiation of rule
making procedures for such modification is unwarranted for the following reasons:

1.           Current Federal regulations, prescribing requirements for the characteristics,
application and installation of pressure relief devices, provide adequate and appropriate levels of
safety. Federal Standard, 49 CFR Section
192.11, incorporates NFPA Standards No. 58 and 59 by reference but significantly prescribes that
Part 192 shall
prevail in the event of conflict. Paragraph (b)(3) of Section 192.11 particularly provides that
discharge vents from relief valves must be located so as to prevent any accumulation of gas at or
belowground, and 49 CFR Section
192.199(e), reinforcing this requirement, specifies that a pressure relief device must have
discharge stacks, vents, or outlet ports located where gas can be discharged into the atmosphere
without undue hazard.

Numerous other requirements of Part 192 and NFPA 58 provide extensive coverage of the design,
application, and installation of relief devices, and since relief devices may not be installed
where discharged gas will
accumulate on the ground or cause undue hazard, the expressed central concern is null.

2.           Pressure relieving devices in most instances are the only practicable means of
providing overpressure protection for vaporizers, containers, and hydrostatic relief between
valves. NFPA 58 Section 314 requires that regulators used to control distribution or utilization
pressure be as close to the container as practicable. Since other required pressure relieving
devices would be present, all in the same general area, little, if any, benefit would derive from
the exclusion of the one relief device on the distribution system.

3.           In certain circumstances, such as a small closed distribution system, a pressure
relief device may be the best means of assuring safety from overpressure.

4.           Constraints imposed by the Office of Pipeline Safety Operations (OPSO) on an
operator's design flexibility are inappropriate where commensurate safety benefits are not evident.

We hope that this explains OPSO's position to your satisfaction and provides information which may
be of help in deter- mining whether an installation is in compliance with Federal regulations.

Sincerely, SIGNED
Cesar DeLeon Acting Director Office of Pipeline Safety Operations
Arizona Corporation Commision
222 West Encanto Blvd., Suite 210
Phoenix, Arizona 85009

June 23, 1976

Mr. Cesar DeLeon
Office of Pipeline Safety Operations Department of Transportation Washington, D.C. 20590

Dear Cesar:
In a piped gas propane system during the summer time, the pressure on the LP storage tank is over
60 pounds. I have cited LP companies in the past for the lack of over-pressure protection of their
distribution systems when fed with a single regulator set at 15 pounds. As a result, most have
installed monitor regulators. However, one company is planning on a relief valve. As I read the
rules, there are three choices (condensed to simplify) that are legal to provide protection:

(1)         A monitor regulator

(2)         An automatic shutoff valve

(3 )        A relief valve
For a situation such as this a shutoff valve (2 above) is obviously undesirable as you lose the gas
pressure in the system;
and the system relight procedure must be implemented which is quite costly and disturbing to
customers.

I cannot condone the use of a relief (apparently legal) as it spills LP gas which is heavier than
air, thus causing a hazard due to the ground hugging characteristics. In this case the relief valve
discharge is in a somewhat remote area; but, for example, one can never be sure where kids will be.

To protect the system with monitors would be better, but with the vaporizer and piping arrangement
at least three monitors would be required. Therefore, the operator is installing a relief valve on
the inlet to the system.

I am suggesting that your technical section review the situation and make rule changes to eliminate
the use of relief valves on piped LP gas systems except when used as a second over-pressure device
downstream of a monitor and working regulator combination and as required on LP storage tanks.
Sincerely,
ARIZONA CORPORATION COMMISSION H. R. Garabrant, P.E.
Gas Utilities Safety Engineer
Utilities Division

Regulation Sections