LAC 43:XI.4309. Internal Design Pressure (Formerly §1309)

A. Internal design pressure for the pipe in a pipeline is determined in accordance with the following formula. P = (2St∕D) × E × F P = internal design pressure in pounds per square inch gauge S = yield strength in pounds per square inch determined in accordance with Subsection B of this Section t = nominal wall thickness of the pipe in inches D = nominal outside diameter of the pipe in inches E = seam joint factor determined in accordance with Subsection E of this Section F = a design factor of 0.72, except that a design factor of 0.60 is used for pipe, including risers, on a platform located offshore or on a platform in inland navigable waters, and 0.54 is used for pipe that has been subjected to cold working to meet the specified minimum yield strength and is subsequently heated, other than by welding or stress relieving as a part of welding to a temperature higher than 900° F (482° C) for any period of time or over 600° F (318° C) for more than one hour. B. The yield strength to be used in determining the internal design pressure under Subsection A of this Section is the specified minimum yield strength. If the specified minimum yield strength is not known, the yield strength is determined by performing all of the tensile tests of API Standard 5L on randomly selected test specimens with the following number of tests. Pipe Size | Number of Tests Less than 6 inches in outside diameter | One test for each 200 joints 6 inches through 12-3/4 inches in outside diameter | One test for each 100 joints Larger than 12-3/4 inches in outside diameter | One test for each 50 joints If the average yield-tensile ratio exceeds 0.85, the yield strength of the pipe is taken as 24,000 psi. If the average yield-tensile ratio is 0.85 or less, the yield strength of the pipe is taken as the lower of the following: 1. 80 percent of the average yield strength determined by the tensile tests; 2. the lowest yield strength determined by the tensile tests. C. If the nominal wall thickness to be used in determining internal design pressure under Subsection A of this Section is not known, it is determined by measuring the thickness of each piece of pipe at quarter points on one end. However, if the pipe is of uniform grade, size, and thickness, only 10 individual lengths or 5 percent of all lengths, whichever is greater, need be measured. The thickness of the lengths that are not measured must be verified by applying a gage set to the minimum thickness found by the measurement. The nominal wall thickness to be used is the next wall thickness found in commercial specifications that is below the average of all the measurements taken. However, the nominal wall thickness may not be more than 1.14 times the smallest measurement taken on pipe that is less than 20 inches in outside diameter, nor more than 1.11 times the smallest measurement taken on pipe that is 20 inches or more in outside diameter. D. The minimum wall thickness of the pipe may not be less than 87.5 percent of the value used for nominal wall thickness in determining the internal design pressure under Subsection A of this Section. In addition, the anticipated external loads and external pressures that are concurrent with internal pressure must be considered in accordance with §§4311 and 4313 and, after determining the internal design pressure, the nominal wall thickness must be increased as necessary to compensate for these concurrent loads and pressures. E. The seam joint factor used in Subsection A of this Section is determined in accordance with the following table. Specifications | Pipe Class | Seam Joint Factor ASTM A53 | Seamless Electric resistance welded Furnace lap welded Furnace butt welded | 1.00 1.00 0.80 0.60 ASTM A106 | Seamless | 1.00 ASTM A333 | Seamless Welded | 1.00 1.00 ASTM A381 | Double submerged arc welded | 1.00 ASTM A671 | Electric-fusion-welded | 1.00 ASTM A672 | Electric-fusion-welded | 1.00 ASTM A691 | Electric-fusion-welded | 1.00 API 5L | Seamless Electric resistance welded Electric flash welded Submerged arc welded Furnace lap welded Furnace butt welded | 1.00 1.00 1.00 1.00 0.80 0.60 1. The seam joint factor for pipe which is not covered by this Paragraph must be approved by the commissioner. F. Piping systems designed for operation at high stress levels shall be analyzed for potential propagating fractures. Methods of limiting the extent of such fractures shall be applied where warranted.