Minnegasco — Pipeline Safety Interpretation

Page 1September 13, 1993 Mr. Eugene F. Schultz Minnegasco 6161 Golden Valley Road Minneapolis, MN 55422 Dear Mr. Schultz: Your letter of June 29, 1993, requests an interpretation of 49 CFR 192.201(c). You asked if it is acceptable to position a relief valve between two regulator stations located near each other to protect the system from overpressure. The regulator stations both supply low pressure gas to the same gas distribution system. The configuration you describe may be acceptable. You must demonstrate that the common relief valve has the capacity to limit the maximum pressure in the main to a pressure that will not exceed the safe operating pressure for any connected gas utilization equipment. The relief valve must have the capacity to protect the system if the largest volume regulator station fails wide open. Pressure loss in the section of main between each of the two stations and the relief valve must be considered so that the pressure in the main at each station complies with §192.201(a) (1). This could be a problem, particularly if the mains are old and have excessive accumulations of dirt, sediment, etc. Verification of relief valve capacity must also verify the absence of excessive pressure loss of this kind. We trust that this responds satisfactorily to your request. Sincerely, Cesar De Leon Director, Regulatory Programs Office of Pipeline Safety dal\192.201\93-09-13#