Tuesday, May 25, 2010

Anonymous comments

I, like many others, are weary of the battle between those for and against the -0.850V "ON" criteria (yes yes with reference to a CuCuSO4 reference cell).

I do lean towards the science side of the debate, but also recognize that a lab is not the same as in the field, and practical measures are required in the field.

IMHO, a -0.85V "ON" criteria specifically for galvanic anode CP systems in soils above some soil resistivity (pick a number based on science 2000? 5000? ohm-cm)will protect the pipe. The amount of current an anode can generate would not be able to produce a significant IR drop, hence by default "considers" those drops other than those across the electrolye boundary.

Providing a sound basis that allows the operator to use the -0.85V "ON" criteria addresses the concerns I hear at the meetings. It provides the operator a safe criteria, supported by sound science, and give a valid/supported stance to take with a regulator. Most importantly, it provides for a procedure that can be performed cost effectively, repeatably, correlates with the historical data.

This is no different than what I hear others say they do. It just documents the process, brings some consensus and consistancy to the approach, and moves us forward on this standard.

Why is this important to some many operators? The practical issue, as I see it, are associated with trying to measure an "instant off" value on a pipeline that is protected by galvanic anodes that are cad welded to the pipeline. This is very imparactical to interrupt. Even if they the anodes came up into a test station, just the vast numbers of anodes involved make it an impractical test procedure to perform (how many interrupters would it take?). In many cases, we wouldn't even be allowed to dig down just to break the anode wire connection.

Besides the impractical nature, it is not warranted in these low current situations.

I propose a study to establish some norms for when the -0.85 ON criteria would be acceptable. Tables could be generated that might correlate soil resistivity, "typical" anode current flow, and "expected" IR drops associated with those currents. This should meet the concerns of most folks. Guidance could be provided if an operators system were outside of those norms.

Of course this is not 100% iron clad. There could be scenarios where interference could be involved, thus the "ON" reading might not be real, but this is no less true of any CP system, even with "instant off" readings. No criteria eliminates the need for knowledgeable CP personnel to monitor and interpret the results.

Standards of any kind do not lend themselves to performing a task in the most precise way, but takes complicated processes and builds in enough of a safety factor that it becomes a practical rule book to use in most cases. We always depend on knowledgeable folks to know when the "rules" or standards are applicable for a given situation.

No comments: