On Nov. 17, new rules took effect increasing the maximum allowable operating pressure (MAOP) for natural gas transmission pipelines beyond that allowed by previous regulations. The Pipeline and Hazardous Materials Safety Administration (PHMSA) rule update amends 49 CFR 192 to reflect improvements in pipeline materials, assessment tools, and maintenance practices over the past 25 years.
The final rule will apply to both new and existing pipelines posing a low safety risk based on location, construction, and materials. He also will remove PHMSA from granting case-by-case special permits allowing operation of particular pipeline segments at higher MAOP.
PHMSA began special permitting in conjunction with its 2003 issuance of gas transmission integrity management regulations. A class location waiver allowed an operator to maintain operating pressure on a pipeline following an increase in population, changing its class location, given the operator’s ability to demonstrate an alternative integrity management program for the affected pipeline.
Waivers would only be granted when pipe condition and active integrity management provided a level of safety greater than or equal to pipe replacement or pressure reduction, according to an Apr. 23, 2004, PHMSA statement.
Absent a waiver, the operator would have to either reduce pressure or replace the pipe with thicker walled pipe. The first three pipelines to receive special permitting for segments of their systems were Maritimes & Northeast, Rockies Express, and Alliance, all granted July 11, 2006.
Precedent
Both Canadian and British standards have long allowed operation of pipelines at higher stress levels. The Canadian pipeline authority has allowed higher stress levels since 1973, while roughly 1,140 miles of the UK’s Northern pipeline system have operated at higher levels for the past 10 years.
In the US, some 5,000 miles of gas transmission lines have operated at higher MAOP since initially being grandfathered when federal pipeline regulations were adopted in the 1970s.
PHMSA bore these examples in mind both when considering individual waivers and when codifying them into new regulations.
Change
The new regulations boost operating pressure for qualifying pipelines in Class 1 areas to 80% of specified minimum yield strength (SMYS) from 72%. The Class 2 ceiling rose to 67% from 60% for qualifying pipelines, with Class 3 increasing to 60% from 50%.
Several types of pipeline will not qualify for a higher MAOP, including:
- Segments in densely populated Class 4 locations.
- Grandfathered segments already operating at higher MAOP but not constructed to modern standards.
- Pipe experiencing failures suggesting a systemic problem during initial hydrostatic testing.
- Pipe manufactured by low-frequency electric welding.
- Segments that cannot be internally inspected.
- Non-steel pipe.
- Bare pipe.
- Pipe with wrinkle bends.
Adoption of the prior standards for calculating MAOP on gas transmission pipelines occurred in 1970 as part of the original set of pipeline safety regulations established as federal law.
Beyond the improvements in materials, tools, and maintenance practices seen since, PHMSA pointed to pipeline operators’ implementation of integrity management programs as improving both the industries’ understanding of the risks it faces and its ability to reduce these risks in issuing the new rules.
PHMSA also cited the success of case-by-case special permit proceedings in Class 1, 2, and 3 areas as showing the viability of enacting more general standards officially codifying the rule changes allowed in these cases.
In addition to being located in Class 1, 2, or 3 locations and being required to meet the new design and construction requirements set forth in the amended CFR 192, pipelines wishing to operate at a higher MAOP will need:
- Supervisory control and data acquisition (SCADA) systems that include the monitoring of line flow and pressure, compressor start-ups and shutdowns, and the ability to remotely close valves.
- No mechanical couplings used in place of girth welds.
- No failures during normal operations indicative of a systemic fault in materials as determined by root-cause analysis.
- If constructed before Nov. 17, to have subjected at least 95% of girth welds to nondestructive examinations.
The new rules are well timed, increasing the efficiency of the US natural gas transmission pipeline network while maintaining its safety at a time when the capital available for either building new capacity or repairing existing facilities is limited. PHMSA estimates about 3,500 miles of existing pipeline and 700 miles of pipeline built each year will use an alternative, higher MAOP.