SKF Microlog Analyzer CMVA 60 ULS for Drilling Platform Anchor Winches

Background

Drilling for oil in deep water requires some unique equipment to provide the stability needed for the drill platform during operations. Using a combination of cable and anchor chain, four or more anchors are placed by tugboats several thousand feet from the platform. After the anchors are secure, the cable is retracted until taut. Maintaining this tension provides the stability for operations.

The cable and anchor chains weigh approximately 149 kg/m (100 lbs./ft.) so that the cable winch is a massive device of over 113 000 kg (250 000 lbs.). The cable drum, which is electrically driven through a gearing arrangement, has the support bearings mounted into the inside radius of the drum, resulting in a rotating outer ring for the bearing and a stationary drum shaft. 

During normal operations, the drum rotates at 10 r/min on two different bearings, an SKF 23292CA and an SKF 24064CC.  Once the drilling rig is in place, it will remain in place until there is some requirement to move, possibly many months. Environmentally, the bearings are in trouble from the day the tension is set because they may not rotate again until the platform is moved. As with any bearing, inactivity is hazardous to its health, and when it is in a damp, variable temperature location, condensation will occur and result in damage to the bearing rings. In addition, during storms, salty sea-water is blown over the bearings and seeps into the internal parts. Water etching will result, which leads to spalling and an ultimate catastrophic bearing failure.

This is what had happened to a rig in the Gulf of Mexico. The resultant damage from the bearing failure included dropping several thousand feet of the anchor chain, which required a special recovery ship at an expense of over $2,000,000 USD, plus repair and lost production cost. The owners then asked us if we could inspect the winches on a rig under construction at a dry dock in Texas. The winches had been installed early in the construction and had been inactive for over six months.