Department of Transportation/Pipeline Hazardous Materials Safety Administration
(PHMSA) published “Guidelines for Integrity Assessment of Cased Pipe for Gas
Transmission Pipelines in HCAs” as well as the FAQs for this document on March
1, 2010. PHMSA worked with a group of state regulators, representatives from
industry, trade associations, and other stakeholders to develop guidelines for
performing External Corrosion Direct Assessment (ECDA) of gas transmission pipe
inside casings. These guidelines are intended to assist operators in complying
with 49 CFR 192, Subpart O for cased pipe in HCAs.
Cased pipe presents significant challenges to conducting a successful integrity assessment using ECDA/CDA, especially with regard to step 1 (region identification and indirect inspection tool selection), step 2 (indirect assessment) and step 3 (direct examination) of the 4-step process. The 4th step in the ECDA process is post assessment.
For cased pipe, PHMSA considers the following data critical to the success of the ECDA process. This data is important for proper selection and use of indirect inspection tools, ECDA region identification, feasibility determination, use and interpretation of indirect inspection tool results, and selection of casings for direct examination.
- Data needed for indirect tool selection,
- Data needed for region identification,
- Data on casing construction,
- For filled casings, type of fill material,
- Casing monitoring data (for example, if the casing is shorted, or wax fill is in poor condition),
- Operating conditions (operating pressures above 60% SMYS and operating temperatures above 120° F should be considered higher risk),
- Coating type and condition (note: these guidelines may not be used if the carrier pipe is bare, i.e., uncoated),
- History of metallic shorts and/or electrolytic contact.
The guidelines in this document address considerations for
tailoring the ECDA methodology to conditions specific to cased pipe. Indirect
inspection tools have limited ability to detect corrosion activity and/or
coating holidays reliably for pipe inside casings. The guidelines also address
the additional considerations for the selection of indirect inspection tools
when conducting ECDA on cased pipe.
For cased pipe, region identification can be particularly problematic. PHMSA has developed guidelines for assuring that all casings in a single region are sufficiently similar, as specified in NACE RP 0502-2002, §126.96.36.199.1, while still maintaining enough flexibility to allow the grouping of casings (where warranted) into a single region.
Exhibit C of these guidelines provide supplementary guidance on special considerations, cautions, engineering considerations, and limitations that should be taken into account when using, interpreting, and analyzing the results of indirect inspection tools used to assess cased pipe. PHMSA has previously released guidelines for using, interpreting, and analyzing the results of GWUT used to assess cased pipe.
The other assessment activities (such as monitoring casing integrity) supplement the indirect inspection tool data with additional data which is indicative of the effectiveness of engineered systems (such as casings, end seals, and wax fill) in preventing corrosion and protecting carrier pipe integrity. PHMSA has identified guidelines for these other assessment activities in order to:
- Compensate for the limited effectiveness of indirect inspection tools when conducting indirect inspections of cased pipe and,
- Assist the analysis of indirect assessment results and allow the selection the highest risk casings for direct examination.
For a copy of the Guidelines or FAQs, contact Jessica Roger.