{"operation":"document","citation":"PI-70-024","title":"Missouri Power and Light Company — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1970-12-21","effective_on":null,"summary":"PI-70-024 response to Missouri Power and Light Company concerning 192.105.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-70-024.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-70-024.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-70-024","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1970/PI70024.pdf","body":"<<<PAGE 1>>>\n\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\ncurrent 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 plan perpendicular to\nthe 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 basic 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, for instance, the pipe being installed\nDB\nC:\\WP51\\INTERPRT\\192\\105\\70-12-21\n1\n\n<<<PAGE 2>>>\n\nis 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 the, nondestructive testing of welds is required where the\noperating pressure will produce a hoop 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\nC:\\WP51\\INTERPRT\\192\\105\\70-12-21\n2","truncated":false,"body_characters":2845}