A high priority for operators of subsea cables is avoiding the cost of downtime. To help ensure that your equipment remains in good working order, we present a 5-step plan for inspecting and testing your cables, along with some tips and troubleshooting advice about when to call for help.
In this blog, we will cover ways to visually inspect your marine cables to ensure that they continue to operate according to design.
Performing a Visual Inspection
Many issues can cause a cable to leak or fail when deployed on the open sea. A severe storm, an electrical short, or even a shark bite can disrupt the electrical and/or optical connection to the ship.
Cables should be inspected regularly throughout their service life as part of standard operating procedures to ensure your equipment remains in good condition. We recommend inspecting a cable before major operations, offshore shipping, and storage. We also advise keeping a cable log that records the hours of use, faults, maintenance, and inspections. In some cases, photos of the damage and diagnostic test results can give the field service engineer onshore enough information to coach the crew aboard to perform the repair.
A visual inspection is crucial to discovering minor or major damage to the cable or termination. To visually inspect the entire cable length, it must be fully reeled in or out. Every time a cable is spooled, deployed or recovered, the outer jacket should be looked over closely. This prevents the need for additional inspections and ensures that any outer jacket damage is known.
During a visual inspection, check for loose wires, kinks, and “birdcages” in the cable, that need to be addressed. If the cable is pulled tight, the loops will reduce in size until the cable bends to such a sharp angle it cannot recover. The cable must therefore be kept straight from the shipping drum to the winch drum before the winding operation starts.
Bending a cable containing an air hose to a small radius can cause the hose-liner to kink and generate a weak point in the liner which may fail later under pressure. Damage to the hose braid also can create weak points where the liner blows through when pressurized. Never use a damaged cable containing an air hose (for example a source umbilical cable) as it could pose a life-threatening risk.
Locating Faults in the Cable
When performing the inspection, use a proven method for measuring cable length so that the position of any damage found can be accurately recorded. Cable length can be measured by equipment built into the winch or by a mechanical clock and wheel resting on the cable.
External damage is often an indicator of the location of a leak in the cable. This can be useful as low isolation cannot be linked to TDR measurements. When digital cables are used and the location of outer damage is known, low isolation can be verified by measuring the fibers. Very often a digital cable with low isolation and outer damage will show an event in the fiber attenuation which can be measured. When the calculated length of the event covers the length of the external damage you can be sure this is the low isolation area.
The best way to prevent unwanted downtime and save money on new equipment for your marine operations is to follow expert advice on maintaining your existing equipment. Working with your supplier will ensure your equipment remains operational during its full lifetime, saving you time and money in the long run.
Practical Guide to locating defaults quicker
For more practical tips to detect errors faster and more efficiently, our cable experts created a Seismic Guide on Cable Handling. Download it below and request your own sidekick in Visual Inspection: