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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #PI-03-0100 ([Pacific Gas and Electric Company] [Shan Bhattacharya])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: Pacific Gas and Electric Company

Individual Name: Shan Bhattacharya

Location State: CA Country: US

View the Interpretation Document

Response text:


U.S. Department of Transportation
Research and Special Programs Administration
400 Seventh Street, S.W.
Washington, D.C. 20590

February 14, 2003

Mr. Shan Bhattacharya, P.E.
Vice President, Engineering and Planning
Pacific Gas and Electric Company
123 Mission Street, Room 1521
San Francisco, CA 94105

Dear Mr. Bhattacharya:

This is in response to your request of July 29, 2002, for an interpretation of the gas pipeline atmospheric corrosion requirements at 49 CFR § 192.481. You ask whether it is the intent of this section to require operators to monitor for atmospheric corrosion "in areas that are not subject to atmospheric corrosion."

Section 192.481 states that operators shall evaluate each onshore pipeline that is exposed to the atmosphere at least every three years and take remedial action whenever necessary to maintain protection against atmospheric corrosion. This section does not exempt pipelines that are in areas initially determined to have a noncorrosive atmosphere under § 192.479, but rather requires periodic evaluation of all pipelines exposed to the atmosphere.

Corrosion can, and does, occur in areas that, in general, have a noncorrosive atmosphere. Local moisture conditions, chemicals in the environment, and air-soil interfaces may result in severe corrosion in areas where corrosion is not expected. Periodic evaluation is necessary to identify and remediate these conditions for every pipeline facility exposed to the atmosphere. This requires an investigation of the conditions that exist in the immediate area of an exposed pipeline. A general or regional determination that a corrosive atmosphere does not exist is insufficient to meet this requirement.

Pacific Gas and Electric (PGE) appears to be basing its determination of "zones or areas of its service territory where a corrosive atmosphere exists" solely on regional moisture conditions. If that is the case, it has not considered all conditions that can lead to corrosion. Furthermore, § 192.479 does not establish a two-class system for the periodic corrosion inspections—one for pipelines in areas documented to be noncorrosive and one for areas subject to corrosion. Even for areas with a generally noncorrosive atmosphere, periodic evaluations are required to ensure that local conditions are not causing atmospheric corrosion.

Therefore, all pipeline facilities exposed to the atmosphere must be periodically monitored for evidence of atmospheric corrosion. A general determination of broad zones of noncorrosive atmospheric conditions based on a sample survey may be useful, but does not fully meet the intent of § 192.481, which requires periodic evaluation of each pipeline exposed to the atmosphere. Inspection data gathered during routine service calls, patrols, and five-year leak surveys can be used to meet this requirement, provided personnel performing these tasks are qualified to inspect for corrosion.

If you have any further questions about the pipeline safety regulations, please contact me at (202) 366-4565.


Richard D. Huriaux,
P.E. Manager, Regulations
Office of Pipeline Safety

Regulation Sections

Section Subject
192.479 Atmospheric corrosion control: General