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Interpretation Response #PI-71-088 ([Cathodic Protection Service] [Ted L. Canfield])

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

Interpretation Response Details

Response Publish Date:

Company Name: Cathodic Protection Service

Individual Name: Ted L. Canfield

Location State: TX Country: US

View the Interpretation Document

Response text:

December 20, 1971

Mr. Ted L. Canfield
Senior Project Manager
Cathodic Protection Service
P.O. Box 66387
Houston, Texas 77006

Dear Mr. Canfield:

In reply to your letter of November 18, 1971, to Lance Heverly, following are our comments on
your interpretation of certain sections of Subpart I, the corrosion part of our Federal gas pipeline
safety standards.

Your letter states:

"(a) Bare piping (distribution or transmission) under influence of impressed current
protective systems:

Initial survey and resurvey to consist of acquiring structure-to-earth potential
measurements at maximum 20' intervals over the entire length of line or system being influenced
by a given impressed current system. This resurvey procedure to be conducted on an annual

(b) Bare piping (distribution or transmission) under complete protection with magnesium
anodes (i.e., supposed protection of entire surface area):

Initial survey and resurvey procedure to be same as outlined above for bare piping
under influence of impressed current protective systems."

It is our position that when a bare distribution or transmission pipeline is under full cathodic
protection, regardless of whether the protection is provided by an impressed current type system
or by galvanic anodes, the system must be checked at least once a year in accordance with Section
192.465(a) and the level of cathodic protection must meet the requirements of Section 192.463.

We do not stipulate any distance intervals for making pipe-to-soil potential measurements.

Although checking at 20-foot intervals may be appropriate in some instances, conditions could be
such that no less than continuous inspection would be necessary. Our requirement is that the
cathodic protection system must protect the pipeline in its entirety. It is the operator's
responsibility to determine what spacing is required between pipe-to-soil potential measurements
to ensure that the pipeline is protected in its entirety. (If your firm is the consultant to a gas
operator, the operator will be looking to you for advice as to what spacing frequency is necessary
to comply with the regulations.)

"(c) Bare piping (distribution or transmission) which has been electrically surveyed to
determine areas of current discharge and subsequently provided with galvanic anode installations
("hot spot" protection) at points or areas of previously determined current discharge.

Resurvey procedure to consist of resurveying annually 10% of a given system or
line to determine that the structure is receiving a net protective current at the previously
determined current discharge points. A different 10% is to be surveyed each year so that the
entire system will have been resurveyed within a ten year period.

Further, that, at intervals not exceeding three years, a complete survey to be
conducted over the entirety of a given bare line or system under "hot spot" protection to
reevaluate unprotected portions and protect where active corrosion is detected. (This would
appear to be somewhat in conflict with the 10% per year resurvey program). By way of
commentary here, we can see that this requirement as written could certainly prove to be very
wasteful of scarce technical manpower. If the reevaluation survey is to be meaningful, so as to
pick up the possibly one newly developed "hot spot" areas every three (3) years for each 100
originally detected, it must still be conducted as thoroughly as the original survey."

With regard to the first two paragraphs of your statement (c), we wish to point out that the 10%
resurvey per year applies only to separately protected service lines or to separately protected short
sections of mains not in excess of 100 feet (Section 192.465). The 10% resurvey does not apply
to "hot spot" protection. Monitoring tests of "hot spot" protected sections of electrically
continuous pipelines must be made each year. (After all, this would require less work than
checking a bare pipeline that is cathodically protected in its entirety using galvanic anodes as
described in your statement (b).)

With regard to the third paragraph of your statement (c), when "hot spot" protection is involved,
the operator must resurvey his bare pipeline at intervals not exceeding three years, and provide
cathodic protection in each area where active corrosion is found (Section 192.465(e)).

Your letter also asked about the estimated date when the existing HM-6 code for liquid pipelines
will conform to the present natural gas code in respect to corrosion control. Although we may in
the future make those requirements essentially the same, we do not at this time have a schedule
for the necessary rule-making action. However, in regard to the questions which you have raised,
the two codes are quite similar. In the case of gas pipelines, complete resurveys are required
every three years instead of every five years as required for liquid pipelines.
In response to your question about gathering lines, the Natural Gas Pipeline Safety Act of 1968
requires that gathering lines in non-rural areas must meet our safety regulations. Section 2(3) of
the Act gives a detailed explanation of non-rural locations (copy of Act enclosed).

I trust this information will be helpful to you.


Joseph C. Caldwell
Acting Director
Office of Pipeline Safety

Regulation Sections

Section Subject
192.463 External corrosion control: Cathodic protection