(Revised 04/01/07)

To date in the transportation of corrosive liquid industry, a conductivity test is generally used to verify the integrity of tank car interior linings. Now there is a better method for verification of tank car interior lining integrity. It is the Liner Monitoring System (LMS). The LMS design incorporates the following.

The LMS was designed accepting the fact that rubber linings and coatings inside tank cars conduct electrical signals. It is true that rubber linings and coating materials are not very good electrical conductors but they are conductive.

Actually there is a test, ASTM D991, for measuring the volume resistivity of rubber lining materials. Using this test we can measure the volume resistivity (ohm-cm) for a rubber lining material. As we know, resistance is directly proportional to the length of the conductor, increasing the length of a conductor is similar to combining resistors in series. Further, resistance is also inversely proportional to the cross-sectional area, increasing the cross-sectional area is similar to combining resistors in parallel, which is known as the equivalent resistance of parallel groups. Using the volume resistivity value and the cross-sectional area, a rough equivalent resistance calculation is possible for the rubber lined area of a tank car. So, rubber linings and coating materials are electrically conductive and the larger the surface area of the tank lining exposed to the conductive liquid, the lower the equivalent resistance value.

The LMS generates a conditioned signal at a controlled frequency. This is in effect an alternating current (ac). The signal generated by the LMS does not polarize the circuit like direct current (dc) signal.

In the bulk electrolyte current is carried by ions. If a dc signal is imposed upon a chemical cell, chemical reactions can occur at the electrodes. If an ac rather than a dc is used, the chemical reactions that take place on the half-cycle, are reversed on the following half-cycle. It is generally accepted that measurements of ionic conduction are made by ac techniques to avoid complications of processes taking place at the electrodes.

The signal direction of the LMS is from the instrument through the probe, the conductive liquid, the lining, the shell and back to the instrument. Then the LMS reverses the signal direction. So, the LMS signal will neutralize any possible capacitive reactance and/or galvanic potential in the case of a liner breach.

A rubber lined steel tank car is an electrochemical cell. But because only one electrode is exposed directly to the electrolyte and the other covered with the rubber lining, it tends to resist the chemical reactions and thereby the electrochemical reactions that accompany dissimilar metals in an electrolyte. However, when the rubber lining is breached and the steel shell electrode becomes exposed to the electrolyte, these chemical and electrochemical reactions are present.

In the case of the LMS, the large electrode is steel (the shell or tank) and the relatively smaller electrodes are graphite (the probes). The LMS uses two graphite probes and two tank connections. The processor program measures and displays the probe to probe (P/P) resistance, the tank to tank (T/T) resistance and the probe to tank (P/T) resistance. Even when chemical and electrochemical reactions are present, the LMS will still monitor the lining because the signals are conditioned at a controlled frequency and are impressed in both directions. In one direction it will add any galvanic potential and in the other direction it will subtract the same. It will null out the galvanic potential.

The US Patent and Trademark Office issued a patent on December 16, 2003 for the LMS, U.S Registration No. 6,662632. We think the LMS is a superior device for verifying the integrity of elastomer linings in tank cars, cargo tanks and stationary tanks. For further information on the LMS please call Terry Parker at (772) 234-2993, via e-mail at or visit our website