Proper adhesion is key to maintaining a watertight splice. Under deep ocean pressure, water can migrate along the interface between the cable and the potting compound. This ingress can eventually lead to cable failure or, worse, a short circuit. A well executed splice is shown in the figure above - note that the cable is bend without producing any gaps.
Adhesion is primarily determined by the characteristics of the cable jacket materials and surface preparation.
As usual, our discussion applies to smaller cables used for low-voltage power and communications. Subsea cables for power transmission, which are oil-filled and armored, are not within our scope.
Cable outer sheath materials used in many subsea applications include polyurethane, polyethylene, and chloroprene (neoprene). Standard industrial power and communications cables are typically PVC or polyethylene.
Adhesion can be improved by the following methods:
- Surface roughness: Abrading the jacket with 120-grit emery cloth.
- Cleanliness: Removing any traces of oils or grease with a cleaning agent such as IPA, acetone, or MEK, depending on the jacket material.
- Primers: Enhancing adhesion with additional polymers. We suggest considering Robnor MP335 or Clibond 41, but you should consult with the supplier based on the cable and potting compounds you're using.
Once the cable has been cleaned or primed, it should not be handled before potting. Ensure operators wear nitrile gloves to prevent contamination.
After the potting operation is completed and the assembly is removed from the mold, inspect the join between the potting and the jacket. A properly executed splice should be able to bend without a gap appearing at the interface. Any gap at the interface could create an ingress path, leading to long-term failure.