Interpretation Response #PI-16-0002
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Mr. Nate Chandler
Bureau Veritas North America, Inc.
Industry, Power and Utilities Group
180 Promenade Circle, Suite 150
Sacramento, CA 95834
Dear Mr. Chandler:
In a letter to the Pipeline and Hazardous Materials Safety Administration (PHMSA) dated January 11, 2016, you requested an interpretation of 49 CFR Part 192. You asked what the value for the longitudinal joint factor (E) in 49 CFR 192.113 should be in determining the yield strength (S) for steel pipe in 49 CFR 192.107.
You stated that Part 192 Subpart C - Pipe Design requires that the yield strength to be used in the design formula in 49 CFR192.105 is 24,000 psi if a pipe's specification or tensile properties are unknown. Also, you stated the longitudinal joint factor (E) should be employed in the yield strength calculation because the quality of the material properties, and the quality of joint are two separate and distinct items required to be accounted for the calculation.
You stated that your understanding of §§ 192.107 and 192.113 is that for unknown pipe material with unknown seam, the specified minimum yield strength value used in the denominator of the percent specified minimum yield strength calculation should be 14,400 psi (24,000 x 0.6) using the E value of 0.6. Therefore, you asked if your understanding of the yield strength determination is correct.
In addition, PHMSA asked you to provde us with an example of the numerator and denominator values for yield strength calculations. You responded to our follow up questions on April 4, 2016, as follows:
- You assumed SMYS to be 30,000 psi (no tensile data available) because the operator thinks this is what it should be based on inconclusive records, from 30's, 40's, 50's or 60's or 70's, and has "no tensile," data for these vintages to support 30ksi.
- You stated that the operator is unsure about wall thickness or seam joint of this vintage pipe based on lack of records.
- You asked if the calculation for percentage SMYS is equal to = 30,000/(30,000*0.6) x 100 using the 30,000 psi and E factor of 0.6 in the denominator, or equal to = 30,000/(24,000*0.6) x 100 using 24,000 psi and E factor of 0.6 in the denominator, or equal to = 30,000/24,000 x 100 using 24,000 psi in the denominator and without E factor?
Our responses to your April 4, 2016, email are as follows:
- It is incorrect to assume 30,000 psi for a pipeline without proper records and your calculations would increase the percentage SMYS than decrease it. Per § 192.107(b)(2), a yield strength of 24,000 psi should be used for a steel pipeline with unknown yield strength.
- When a pipe's wall thickness is unknown, the wall thickness is determined by the method used in § 192.109. If a pipe's longitudinal seam type is not known, it is determined using the information in § 192.113.
- Your values chosen for yield strength and related calculations are incorrect. Under § 192.105, an accurate yield strength is required to determine the design pressure of a pipeline. Your calculations are therefore incorrect, as you use an estimated, and inaccurate, SMYS within these calculations.
If you chose to use the §§ 192.107 and 192.113 requirements instead of tensile testing, for unknown pipe material, you must use 24,000 psi yield strength to determine the design pressure in § 192.105. Pipe mechanical properties of diameter, wall thickness, pipe grade (strength) and longitudinal seam type are then used in the design pressure formula of § 192.105, along with any derating based upon operational temperatures and derating factors in § 192.115. If we can be of further assistance, please contact Tewabe Asebe at 202-366-5523.
John A. Gale
Director, Office of Standards
|§ 192.113||Longitudinal joint factor (E) for steel pipe|