{"operation":"document","citation":"PI-71-008","title":"United Natural Gas Company — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1971-01-20","effective_on":null,"summary":"PI-71-008 response to United Natural Gas Company concerning 192.241, 192.719.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-71-008.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-71-008.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-71-008","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1971/PI71008.pdf","body":"<<<PAGE 1>>>\n\nJanuary 20, 1971\nMr. Richard M. DiValerio\nUnited Natural Gas Company\n308 Seneca Street\nOil City, Pennsylvania 16301\nDear Mr. DiValerio:\nThis is in reply to your letter requesting an interpretation of the relationship of 49 CFR, Sections\n192.241(b) and 192.719(a)(2).\nSection 192.241(b) established limited exceptions to the requirement for non-destructive testing\nof all welds on pipe to be operated at 20 percent or more of SMYS, while §192.719(a)(2) deals\nonly with repair welds.\nAs you have mentioned repairs usually consist of replacing a short section of pipe. The tie-in\nwelds on these short sections of pipe are generally more difficult to make and more often\nperformed under adverse conditions. Experience has demonstrated there is a greater need to\nrequire weld quality in these situations.\nTherefore, if these welds are not strength tested, the requirements of §192.719(a)(2) must\noverride the exceptions in §192.241(b).\nThank you for your interest in pipeline safety.\nSincerely,\n/signed/\nJoseph C. Caldwell\nDirector, Acting\nOffice of Pipeline Safety\nDB/dal/192.241\n71-01-20\n1\n\n<<<PAGE 2>>>\n\nDecember 21, 1970\nMr. J. F. Nienhueser\nAdministrative Assistant\nMissouri Power and Light Company\n101 Madison Street\nJefferson City, Missouri 65101\nDear Mr. Nienhueser:\nThis is in answer to your letter of November 4, 1970, requesting information on hoop stress and\nthe current method used by this office for determining hoop stress in steel pipe.\nHoop stress is defined in Section 805.32 of ANSI B31.8 (formerly USAS B31.8) as follows:\n\"Hoop stress is the stress in a pipe wall, acting circumferentially in a plane perpendicular\nto the longitudinal axis of the pipe and produced by the pressure of the fluid in the pipe.\"\nThe hoop stress, then, is an action which is attempting to pull the pipe apart in a circumferential\ndirection with the \"pull\" being produced on the pipe wall by the internal pressure of the natural\ngas or other fluid in the pipe.\nBarlow's Formula is the common method used to determine hoop stress in the wall of pipe. The\nformula is written as follows:\nS = PD\n2t\nwhere: S = hoop stress, psi\nP = internal pressure, psi\nD = diameter, in.\nt = wall thickness, in.\nThis basis formula written in terms of solving for the pressure is used in Part 192 to determine the\ndesign pressure for steel pipe. The formula, located in Section 192.105, contains factors in\naddition to the basic formula which limit the design pressure in gas pipelines for safety purposes.\nAn example of applying hoop stress in Part 192 would probably be helpful. Section 192.241(b)\nrequires the nondestructive testing of welds on pipeline \"to be operated at a pressure that\nproduces a hoop stress of 20 percent or more of SMYS.\" If, the instance, the pipe being installed\nDB/dal/192.241\n71-01-20\n2\n\n<<<PAGE 3>>>\n\nin Grade B, the SMYS is 35,000 pounds per square inch (psi) and 20 percent of 35,000 psi is\n7,000 psi. For this particular example then, nondestructive testing of welds is required where the\noperating pressure will produce a hoops stress of 7,000 psi or more.\nThe pressure which will produce a hoop stress of 7,000 psi is now determined by using the\nformula in Section 192.105 and solving for \"P\". In this example all of the elements in the formula\nwould be as defined in Section 192.105 except for \"S\" which is no longer the hoop stress at yield\nbut a hoop stress of 7,000 psi, and \"P\" which is no longer the design pressure but the pressure\nwhich will produce a hoop stress of 7,000 psi.\nIf the proposed operating pressure is equal to or greater than the pressure solved for,\nnondestructive testing is required. If the proposed operating pressure is less than this pressure,\nnondestructive testing is not required.\nI hope this explanation answers your questions. If I can be of any further assistance, please\ncontact me.\nSincerely,\n/signed/\nJoseph C. Caldwell\nDirector, Acting\nOffice of Pipeline Safety\nDB/dal/192.241\n71-01-20\n3","truncated":false,"body_characters":3946}