Monitoring relatively new cathodic systems on steel Underground Storage Tanks (USTS) is a very straightforward business. In theory 100% of all systems tested should adhere to the NACE’S standard RP-02-85 (and consequently government compliance) without much difficulty. But an enigma exists in that a relatively small number of tanks are not able to meet that criteria. This paper intends to explore the human element often responsible for the factors which result in non-conforming potential readings.
As a private contractor monitoring cathodic protection systems nationwide, NCT(1) has tested seventeen thousand steel USTS since 1988; all of which are catholically protected by the galvanic anode-cathode method as opposed to the impressed current type. The equipment used for this kind of testing is a copper\copper sulphate reference electrode (RE), one testing reel of 14 gauge copper wire and clamp to connect to the UST, and one polycorder which is a computerized digital direct current voltmeter. An advantage of this type of meter is twofold: one, being digital it has a high input resistance factor that allows for very little voltage drop through the external circuit resistance. And two, this meter allows recording of all results of various tests performed which aids in eliminating human error. Both the reference electrode and the testing reel connect to the polycorder the RE is then placed in nearby soil, while the testing reel is clamped to the UST.
A good portion of the monitoring involves new tanks placed in the ground after September of 1988 and is in compliance with the EPA Federal Regulation Part 280; subpart C--General Operating Requirements, 280.31 (b) (1) which states that ail UST systems equipped with cathodic protection systems must be inspected for proper operation by a qualified cathodic protection tester every three years after installation. Being new, one might assume that one hundred percent of the tested systems would have passed with at least the minimum -850 mV reading. However, a figure closer to a 96% pass rate proved more realistic. What factors account for the 4% non-conforming rate? By observational analysis it is determined that 3% are directly related to human error. This paper will examine those situations. Furthermore, situations will also be examined in which mandated readings were impossible to record caused by the same factor, human error.
To begin the method by which the cathodic protection testis accomplished should be described as a clear understanding of this procedure will prove imperative in providing examples of subpar readings in several instances. Upon arrival at the site the technician immediately assesses whether the test lead (a wire running from the UST upward through the soil inside a manhole marked CP test station) is available or not. If the CP station is available, inside it the leads are connected to a plastic plate to avoid contacting any metal objects such as the metal containment in which the CP station is placed.
