UL 1746 External Corrosion Systems for Steel Underground Storage Tanks

EUROLAB laboratory provides testing and compliance service within the scope of UL 1746 standard. It satisfies the requirements for corrosion protection of steel underground tanks. There are three types of protection systems covered by the standard; tanks with cathodic protection, composite tanks and jacketed tanks. The main tank is constructed in accordance with Standard UL 58 and added more abrasive protection.

UL 1746 Part I Pre-Engineering

Part I of UL 1746 covers pre-engineered cathodic protection systems. The tanks are provided with a galvanic anode. In addition, the filler around the anode specifies the requirements for cable connectors for insulating bushings and core anodes for electrically insulating the tank from the pipes.

The cathodic protection system will be constructed to provide minimum system design based on 4.000 ohm-cm earth resistance. The system consists of dielectric coating applied to all exposed outer tank surfaces, electrical insulating devices (gaskets and bushings) fitted to each tank opening prior to shipment, at least two galvanic anodes per tank, and test station provisions.

UL 1746 Part II Composite Tanks

II of UL 1746. The part covers composite tanks. These are UL 0.100 compliant steel tanks lined with a non-metallic coating at least 58 inch thick. If soil load testing, water load testing and external pressure testing are performed on a sample tank, the steel thickness of the tank can be reduced.

Samples of the composite tank coating system are subjected to air-oven conditioning and immersion in environmental fluids for 30, 90 and 180 days. Samples should retain 80% of the flexural strength value "as taken" after aging.

Samples of the composite tank coating system are subjected to air-oven conditioning and immersion in environmental fluids for 30, 90 and 180 days. Samples should retain 80% of the flexural strength value "as taken" after aging.

In addition, the tank assembly will be subjected to leak testing, tank impact testing and holiday testing. The tank should be subjected to a 5 psi aerostatic leak test and checked for leaks using a leak detection solution. The tank crash test consists of hitting the tank with a 12 pound steel ball. The complete tank assembly is subjected to a holiday test using a 35.000 volt holiday tester.

UL 1746 Part III Jacketed Tanks

III of UL 1746. It covers partially jacketed tanks. These tanks consist of a UL 58 compliant steel tank with a non-metallic outer FRP or thermoplastic jacket. The tank and jacket are separated by an intermediate space where the jacket acts as a secondary containment barrier. The jacket shall be manufactured using a material that is at least 0.100 inch thick.

The complete tank will be subjected to piping test; bending moment and strength test of hoists, tank impact test, leak test, vacation test and ring tight pressure tests as mentioned below.

In addition, a jacketed tank will also undergo an intermediate communication test. During the communication test, a sample is placed underground and filled with water to its capacity. At a point further away from the interground monitoring point, the pressure created by the water and vacuum will add to the interground space. A measurable communication to the monitoring point will be provided within 24 hours.

UL 1746 Part IV Urethane Lined Tanks

IV of UL 1746. Part is currently under development and will include urethane lined tanks. As part of normal production, each tank will be subjected to leakage age testing. Each cathodically protected tank is subjected to an anode continuity test to verify continuity between the anode lead wire and the tank connection. Each composite tank where the FRP is bonded to the steel tank and the areas of the FRP jacketed tanks will be subjected to the holiday test.