The horizontal lube oil cooler consists of a hollow shell with 1240 tubes running through it. Sea water flows inside the shell of the cooler and around the outside of the tubes while the lube oil flows inside the tubes. The water and lube oil never make physical contact. As the water flows through the shell side of the cooler, it picks up heat from the lube oil through the tubes. This cools the lube oil and warms the cooling water as it leaves the cooler. The lube oil must be maintained within a specific operating band to ensure optimum equipment performance. A 0.2mm scale had developed within the cooling water tubes which began to reduce their cooling capacity.