§192.619 – MAOP, lowest of the following.

Recently a question was submitted regarding §192.619(a)(1)(i) and (ii) and where/how these limitations originated.  In particular the operator wanted to know what the reasoning was behind the 200 psi design pressure in (ii).  It was not an easy search, but an answer was finally found.

The text in question is:

(a) No person may operate a segment of steel or plastic pipeline at a pressure that exceeds a maximum allowable operating pressure determined under paragraph (c) or (d) of this section, or the lowest of the following:

(1)  The design pressure of the weakest element in the segment, determined in accordance with subparts C  and D of this part.  However, for steel pipe in pipelines being converted under §192.14 or uprated under subpart K of this part, if any variable necessary to determine the design pressure under the design formula (§192.105) is unknown, one of the following pressures is to be used as design pressure:

(i)  Eighty percent of the first test pressure that produces yield under section N5 of Appendix N of ASME B31.8 (incorporated by reference, see §192.7), reduced by the appropriate factor in paragraph (a)(2)(ii) of this section; or
(ii)  If the pipe is 12¾ inches (324 mm) or less in outside diameter and is not tested to yield under this paragraph, 200 p.s.i. (1379 kPa) gage.

These two paragraphs were amended in 1996 with Amendment 192-78.  The discussion in the NPRM and Final Rule was found in discussion about 192.14 Conversion to Service.  It appears the 200 psi was established considering distribution systems, however as the regulation is written it would apply to all categories of pipelines.

The following are the discussions from these two documents including the proposed and final text of the regulation.

Docket PS-124; NPRM #1 

Section 192.14  Conversion to service subject to this part.  (Also includes changes to §192.553  General requirements.):  Section 192.14 establishes various criteria for qualifying a pipeline previously used in service not subject to part 192 for use under part 192.  Section 192.14(a)(1) requires that the design of the pipeline must be reviewed and, where sufficient historical records are not available, appropriate tests must be performed to determine if the pipeline is in a satisfactory condition for safe operation.  Section 192.14(a)(4) requires that the pipe must be hydrostatically tested in accordance with subpart J to substantiate the maximum allowable operating pressure (MAOP) permitted by subpart L.

Section 192.553 establishes general requirements for increasing the MAOP (uprating) a pipeline.  Section 192.553(d) limits a new MAOP established under part 192 to the maximum that would be allowed under part 192 for a new segment of pipeline constructed of the same materials in the same location.  Neither section provides for verifying design calculations or limiting MAOP when one or more of the steel pipe variables necessary for the determination of design strength or MAOP are unknown.

ANR Pipeline Company suggested using a hydrostatic test to establish the yield strength of pipelines for which yield strength is not known.  The ASME B31.8 Code does not directly provide for hydrostatic testing to determine the yield strength of pipe (ASME B31.8 Code for Pressure Piping for Gas Transmission and Distribution Systems), paragraph 845.214, Qualification of a Steel Pipeline or Main to Establish the MAOP).  However, the Code provides for establishing MAOP on the basis of hydrostatic testing of existing natural gas pipelines or of pipelines being converted to natural gas service where one or more of the factors in the design formula are unknown.  The test pressure used in the referenced Code MAOP calculation is limited to the test pressure obtained at the high elevation point of the minimum strength test segment and to the pressure required to produce a stress equal to the yield strength as determined by hydrostatic testing.  The procedure for determining yield strength by hydrostatic testing is included in B31.8 appendix N, Recommended Practice for Hydrostatic Testing Pipelines in Place.

RSPA proposes to change §§192.14(a)(1) and 192.553(d) to permit verifying the design pressure and establishing a new MAOP for steel pipelines when one or more of the variables necessary for determining those pressures are unknown by (1) testing the pipeline in accordance with ASME B31.8, appendix N, to produce a pressure equal to yield strength, and (2) applying to not more than 80 percent of the first pressure that produces yielding the appropriate factors in §192.619(a)(2)(ii) and proposed §192.619(a)(2)(iii).

The proposed change will enable the conversion or uprating of certain pipelines, or reduce the cost of conversion or uprating of certain pipelines, and will enable the operation of the lines at their fullest potential.
The proposed change should not have an adverse effect on pipeline safety.  To determine the MAOP at a stress equivalent to the yield strength of the pipe in the affected pipelines, testing the lines to hydrostatic pressures greater than otherwise required for the determination of the MAOP under §192.619 will be necessary.  The result will be a greater margin of safety between hydrostatic test pressure and MAOP.  Any defects present in the pipeline will likely fail during hydrostatic testing and be removed from the line.

Proposed text

§192.14  Conversion to service subject to this part.
(a)  *     *     *
(1)  The design, construction, operation, and maintenance history of the pipeline must be reviewed and, where sufficient historical records are not available, appropriate tests must be performed to determine if the pipeline is in satisfactory condition for safe operation.  If one or more of the variables for a steel pipeline necessary to verify the design pressure under §192.105 or to perform the testing under paragraph (a)(4) of this section are unknown, the design pressure may be verified and the MAOP determined by:

(i)  Testing the pipeline in accordance with ASME B31.8 Code, Appendix N, to produce a stress equal to the yield strength, and
(ii)  Applying, to not more than 80 percent of the first pressure that produces a yielding, the appropriate factors in §§192.619(a)(2)(ii) and (a)(2)(iii).

————————————————————————————–

Final Rule, Docket PS-124; Amdt. 192-78

Sections 192.14 and 192.553, Conversion and Uprating.

If a steel pipeline to be converted to gas service under part 192 has not been designed and constructed to meet part 192 standards, it must be converted according to §192.14 (§192.13(a)(2)).  Section 192.14(a)(4) requires that each pipeline must be pressure tested under subpart J of part 192 to substantiate the maximum allowable operating pressure (MAOP) permitted by subpart L of part 192.  Under subpart L, to compute the MAOP of a pipeline being converted, an operator must determine the design pressure of the weakest element of the pipeline (§192.619(a)(1)).

Design pressure is also a factor under §192.553, which establishes general requirements for increasing any pipeline’s MAOP (uprating).  Under §192.553(d), an increased maximum allowable operating pressure may not exceed the MAOP part 192 allows for a new pipeline constructed of the same materials in the same location.  Thus, to uprate a pipeline within this MAOP limit, an operator must determine the design pressure of the weakest element of the pipeline (§192.619(a)(1)).

Because of the role of design pressure, a steel pipeline may not be converted or uprated when any of the pipe characteristics needed to calculate design pressure under §192.105 is unknown.  Therefore, RSPA proposed to amend §§192.14(a)(1) and 192.553(d) to permit the conversion or uprating of steel pipelines based on an approach found in paragraph 845.214 and Appendix N of the ASME B31.8 Code.  Under the proposal, when design pressure is unknown, operators would have to pressure test the pipeline under Appendix N until pipe yield occurs.  The first pressure that produces pipe yield, reduced by 20 percent and the appropriate factor under §192.619(a)(2)(ii), would be used instead of design pressure to calculate MAOP.

Twelve TPSSC members voted for the proposed revision of §192.14, one member supported it with a recommended change, one member opposed it but suggested changes, and one member abstained.  Eleven members voted for the proposal regarding §192.553, two supported it with a recommended change, one opposed it, and one abstained.  The recommended changes were to make yield testing mandatory instead of permissive, and to allow yield testing that is based on other than the “first pressure” that produces yield, since Appendix N does not use that term.  The reasons against the proposal were that yield testing appeared to be mandatory, and use of the Appendix N method should be discretionary.

RSPA has adopted the recommended change regarding mandatory yield testing.  Although, in the proposed rules, yield testing may have appeared permissive, RSPA clearly intended such testing to be the only alternative when design pressure is unknown.  Therefore, in the final rule, if factors in the design formula are unknown, a pipeline to be converted or uprated would have to be pressure tested under Appendix N to determine pipe yield, except as discussed below for low-stress pipe.

The TPSSC member’s recommendation to delete “first pressure” from the proposed rule was not adopted.  Although Appendix N does not refer to the first pressure that produces yield, paragraph 845.214(a)(2) of the ASME B31.8 Code, which applies to the establishment of MAOP when design pressure is unknown, provides that only the first test to yield can be used to determine MAOP.  The proposed rules were consistent with this B31.8 standard, which precludes the use of higher yield pressures that can result from successive testing.

RSPA did not adopt the TPSSC member’s comment that use of the Appendix N method should be discretionary.  When MAOP is determined without knowing the pipeline’s design pressure, conformity to a standardized practice (Section N5.0 of Appendix N) assures additional safety to offset the lack of knowledge about design pressure.
RSPA received comments on the proposed rules from 11 operators and three pipeline-related associations.  Four operators and one pipeline-related association recommended removal of the proposed requirement to use the “first pressure” that produces yield.  Our position on this subject is given above in response to a similar comment by a TPSSC member.

One operator and one pipeline-related association suggested locating the proposed amendments in §192.105 instead of §§192.14 and 192.553.  RSPA did not adopt this suggestion because §192.105 affects the design of new pipelines, a subject the proposed rules did not address.
One operator and two pipeline-related associations argued that pressure testing to yield is unnecessary to qualify low-stress distribution lines (generally lines 123/4 inches or less in nominal outside diameter operating at pressures less than 200 psig) for conversion or uprating.  Part 192 recognizes that low-stress pipelines present a much lower risk to public safety than high-stress lines, all other factors being equal.  For example, certain welding standards in subpart E are less stringent for pipelines to be operated below 20 percent of SMYS.  Because of the lower risk, the final rule provides that pipelines 123/4 inches or less in nominal outside diameter to be operated at a pressure less than 200 psig may be converted or uprated without testing to yield.  The MAOP of such pipelines may be determined under §192.619(a)(1) by using 200 psig as design pressure.

An operator argued that pressure testing to yield should be discretionary, because sufficient safety would be provided by the proposed pressure reduction factors regardless of the level of test pressure.  The commenter was also concerned that pressure testing to yield for an extended time could cause the growth of defects that later cause failure during operation.  Two hours was suggested as the optimum hold time for yield testing, based on ongoing studies.
RSPA did not adopt these comments.  Pressure testing to yield exposes more material and construction defects than does testing to a lower pressure.  With fewer defects remaining after testing to yield, greater long-term protection against failures due to the growth of unexposed defects results.  RSPA intended this extra protection, combined with the proposed pressure reduction factors, to offset the absence of design pressure as a limit on MAOP.  Pressure testing to yield appears to be reasonable since many operators already strength test their pipelines at or above yield for safety and efficiency reasons.  Also, none of the other commenters or TPSSC members objected to pressure testing to yield, except as discussed above for low-stress lines.  As to the optimum hold period for yield testing, because the matter is still being studied by industry and is not addressed by the procedure for yield testing under Appendix N, it is too soon to consider establishing a special hold period for yield testing under part 192.

The final rules have been drafted to improve clarity, to show their relation to design pressure and MAOP under §192.619, and to include the changes discussed above.  The proposed amendments to §§192.14(a)(1) and 192.553(d) are revised and published as an amendment to §192.619(a)(1), because this section deals specifically with design pressure and MAOP.  Final §192.619(a)(1), set forth below, provides that when design pressure is unknown for steel pipelines being converted or uprated, a reduced value of first yield hydrostatic test pressure, instead of design pressure, is used to compute MAOP.  As discussed below, final §192.619(a)(1) does not include the reduction factors proposed for butt and lap welded pipe under §192.14(a)(1)(ii).  If the pipeline to be converted is 123/4 inches or less in nominal outside diameter, 200 psig, instead of design pressure, may be used if the line is not yield tested.  Section 192.553(d) is also revised to refer to amended §192.619(a)(1).  Also, because the 1992 edition of the ASME B31.8 Code is now out-of-print, the 1995 edition is referenced in §192.619(a)(1) as shown by the revisions to Appendix A of part 192 (see below).

31. In §192.619, paragraph (a)(1) is revised to read as follows, paragraphs (a)(4) and (a)(5) are removed, paragraph (a)(6) is redesignated as paragraph (a)(4), and paragraph (b) is amended by removing “(a)(6)” and adding “(a)(4)” in its place:

§192.619  Maximum allowable operating pressure: Steel or plastic pipelines.

(a)  *  *  *  *  *

(1)  The design pressure of the weakest element in the segment, determined in accordance with subparts C and D of this part.  However, for steel pipe in pipelines being converted under §192.14 or uprated under subpart K of this part, if any variable necessary to determine the design pressure under the design formula (§192.105) is unknown, one of the following pressures is to be used as design pressure:

(i)  Eighty percent of the first test pressure that produces yield under section N5.0 of Appendix N of ASME B31.8, reduced by the appropriate factor in paragraph (a)(2)(ii) of this section; or
(ii)  If the pipe is 324 mm (123/4 in) or less in outside diameter and is not tested to yield under this paragraph, 1379 kPa (200 psig).
*  *  *  *  *

All this and more including all the history of the regulations in WinDOT, The Pipeline Safety Encyclopedia.

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