Written by: Brian Pottebaum, Director of Training Services
A metal flex connector is a braided stainless-steel hose fitting typically used to connect the product line to the dispenser or submersible pump. It is designed to minimize vibration as the system operates, as well as to add flexibility to the product line as it enters the sump or manway.
The braided steel mesh protects an interior plastic or steel hose that carries the petroleum. Some of the earlier designs of this fitting were only allowed for underground use by fire code. The installation had to be contained underground, and the flex connector needed adequate protection from corrosion.
Although the braided portion of the flex connector is typically made of stainless steel, the two ends of the fitting are typically not the same grade of steel. The “non-stainless” steel portion of the connector is susceptible to corrosion and can quickly fail if not properly maintained and monitored. Therefore, it is not rated or approved for direct burial (covered with backfill or submerged in water). Constant exposure to backfill or liquid will accelerate corrosion. The same would be true for any metal fitting, like valves, unions, and couplings in the fuel supply system that is not properly protected.
There are two different ways to protect flex connectors from corrosion: Isolation and Cathodic Protection. Both methods may be installed after the original installation, however, the flex connectors should be properly protected when first installed. Modern installations require these fittings to be installed inside secondary containment sumps designed to keep them isolated from backfill and liquid.
If complete separation from backfill cannot be achieved and permanently maintained, then isolation boots can be installed. The boots are placed around the entire flex connector assembly to prevent corrosive agents from making contact with the metal.
There are several different designs of isolation boots. One design includes adjustable ends that can be loosened to allow movement on the product line for correct placement. Another design is a boot that is heat shrunk directly to the flex connector once installed. Isolation boots are a relatively low maintenance means of protection. When the boots show signs of degradation and failure, they must be replaced.
Cathodic protection is the only other option if isolation cannot be accomplished. Some flex connectors were manufactured with an anode already attached, so contact with backfill is not a problem. In fact, constant contact with backfill is required for the anode to work properly. If the factory designed anode is not already attached, cathodic protection can be added in the field. Sacrificial anodes, such as spike/pencil or bracelet anodes, can be connected to the flex connector at the submersible or under the dispenser. A spike/pencil anode is attached with a clamp and driven into the soil/backfill next to the piping. In addition, bracelet anodes can be attached with a U-bolt around the flex connector. In either case, it is required that the anode be buried below the surface to function properly.
PMMIC has documented several flex connector failures. Along with corrosion, other factors contributing to the failures include flex connectors that have been twisted, kinked, or installed with too much bend. The bend is determined by the length of the flexible portion of the connector but should never exceed 90 degrees.
Contact your licensed petroleum equipment installer to determine the best method to protect your flex connectors.
Flex connectors have been viewed as a worry-free link in a fuel delivery system. However, these fittings are not immune to corrosion or wear and tear. Flex connectors must be inspected frequently. Have you inspected your flex connectors lately?