Missouri Public Service Commission — Pipeline Safety Interpretation

Page 1September 16, 1982 Mr. Dale W. Johansen Assistant Director, Gas Department Engineering Section Missouri Public Service Commission Jefferson City, Missouri 65102 Dear Mr. Johansen: The enclosed pipeline safety interpretation has been issued in response to your recent inquiry regarding the relationship between §192.743 and §192.201(a). While your inquiry referred only to relief devices installed before Part 192 became effective, the interpretation applies to all relief devices that are subject to §192.743, and provides that §192.201(a) should not be used to determine the relief capacity needed to comply with §192.743. Sincerely, /signed/ Richard L. Beam Associate Director for Pipeline Safety Regulation Materials Transportation Bureau Enclosure DB/dal/192.743 82-09-16 1#

Page 2No. 82-9 Date: September 16, 1982 DEPARTMENT OF TRANSPORTATION RESEARCH AND SPECIAL PROGRAMS ADMINISTRATION MATERIALS TRANSPORTATION BUREAU PIPELINE SAFETY REGULATORY INTERPRETATION NOTE:A pipeline safety regulatory interpretation applies a particular rule to a particular set of facts and circumstances, and as such, may be relied upon only by those persons tow whom the interpretation is specifically addressed. SECTION: 192.743 SUBJECT: Pressure limiting and regulating stations. FACTS: None QUESTION: Should values for "desired maximum pressure" and "required capacity," as used in §192.743(a) and (b), respectively, be based upon the criteria for pressure relieving and limiting stations set forth in §192.201(a)? INTERPRETATION: Under §192.743, paragraph (a) requires that relief devices at pressure limiting and regulating stations be tested annually to assure they have enough capacity to limit pressure on connected facilities to the "desired maximum pressure." Paragraph (b) provides that if testing is not feasible, the "required capacity" of the devices must be reviewed, calculated, and compared with their rated or experimentally determined capacity. The "desired maximum pressure" of facilities is not defined or specifically regulated by Part 192. However, the operating pressure of a pipeline may not exceed its maximum allowable operating pressure (§§192.619, 192.623) or any lower pressure that might be required as a remedial measure for safety (e.g., §192.485). Thus as long as these limits are not exceeded, the "desired maximum pressure" of facilities is subject to the reduced (due to remedial measures, revision of the maximum allowable operating pressure (§192.611), or any other reason) and testing shows there is insufficient relief capacity to limit pressure to the lower DB/dal/192.743 82-09-16 2#

Page 3level, new or additional relief capacity would have to be installed as required by §192.743(c). The plain language of paragraphs (a), (b), and (c) makes it clear that the purpose of §192.743 is to assure that relief devices at pressure limiting and regulating stations have sufficient capacity to limit downstream pressure to the "desired maximum pressure." It follows that the term "required capacity" in paragraph (b) refers to the capacity of relief devices that is needed to achieve this purpose, and not to a capacity required by §192.201(a). Section 192.201(a) prescribes capacities that apply to the design of pressure relief and limiting stations. The purpose of this rule is to assure that stations are installed with sufficient capacity to prevent accidental overpressure in connected facilities, based on specified safe pressure limits known at the time of design. As operating conditions change, these limits may exceed the "desired maximum pressure" of the facilities. so that additional capacity would be required to meet §192.743. Therefore, the capacity requirements of §192.201(a) should not be used to determine the capacity of relief devices needed to meet §192.743. Richard L. Beam Associate Director for Pipeline Safety Regulation Materials Transportation Bureau DB/dal/192.743 82-09-16 3#