Public Service Commission — Pipeline Safety Interpretation

Page 1November 3, 1970 Mr. F. M. Hoppe Director of Public Utilities Public Service Commission Seven Story State Office Bldg. Lansing, Michigan 48913 Dear Mr. Hoppe: Thank you for your letter of October 14, 1970, concerning construction of two Sections of Part 192, 49 CFR as issued on August 11, 1970. With regard to your first question concerning Section 192.197(c)(4), it is not intended to permit the automatic shut-off device to be located downstream of the service regulator. If this were done, it certainly could cause a ruptured diaphragm in the service regulator which would be dangerous. What is intended is that the shut- off device be located up stream of the service regulator, but controlled by excessive pressure downstream of the service regulator by means of a control line connected from a point downstream of the service regulator. Section 192.197(c)(3), in its second sentence states "The relief valve may either be built into the service regulator or it may be a separate unit installed downstream from the service regulator." No mention is made of a shut-off device downstream of the service regulator. There are service regulator diaphragm, and those would meet the requirements of this section. In regard to the possibility of exceeding 60 psig or 125 psig, depending upon the design of the system, there are requirements in Sections 192.199 and 192.201 for limiting pressures ar regulator stations supplying distribution systems. We are at present actively considering revision of several sections of Part 192 for clarification. Section 192.197(c)(4) will be added to the list for such consideration. With reference to your second question, Section 192.555 does provide an exception to the usual test requirements of Section 192.619 . This exception was provided for in the previous minimum safety standards, the ANSI B31.8 Code §845.23(3) and was apparently believed to be an adequate safety requirement by the B31.8 Code Committee. The exception, in Class 1 locations only, provides that a line may be operated at up to 80% of the pressure allowed for a new line of the same design in the same location. Section 192.555(d)(2)(ii) is subject to the further requirements of Section 192.555(d)(2)(i), which states that a test must be impractical. Section 192.555(d)(2)(iii) places the burden on the operator to determine that the new MAOP is consistent with the condition of the segment of pipeline and the design DB/dal/192.197 70-11-03 1#

Page 2requirements. A new line in a Class 1 location may not be designed for operation at more than 72% of SMYS, (Section 192.1110. Combining the limitations of those two sections leads to the conclusion that a line uprated under the provisions of Section 192.555(d) could only be operated at 57.6% of specified minimum yield strength. Since you have raised the question of the safety of such a procedure the question will be considered for future rulemaking procedures. Sincerely, /signed/ Joseph C. Caldwell Director, Acting Office of Pipeline Safety DB/dal/192.197 70-11-03 2#