High speed has costs, not to the driller, but to the centrifuge owner. Suppose the centrifuge is one pound out of balance. If the centrifuge rotates at 900 RPM, the unbalanced load is 276 lbs, and this unbalanced load is carried by the bearings through to the frame. If it sped up too 1800 RPM, the unbalance load goes up to 1,104 lbs. To keep the centrifuge from shaking itself to death or an early bearing failure, higher speeds require better mechanical tolerances. Generally, to maintain these tolerances over a service life of many years, the centrifuge should be made from stainless steel.

decanter centrifuge

The second problem is stress. All of the mud in the centrifuge is pressing outward putting the bowl and hubs under stress. As the centrifuge is run faster and faster, the stresses build up and can cause catastrophic failure. No decanter centrifuge should be run faster, with a heavier weight mud than it’s designer planned on, and in addition, the structural parts should be in good shape. Corrosion and wear can weaken a centrifuge to the point where it is unsafe at any useful speed. Higher speeds require high strength, corrosion resistant materials.

centrifuge

The third problem is wear. Drilling mud contains grit; it slowly grinds the wearing surfaces of the centrifuge, and eventually enough metal is worn away that the centrifuge must be rebuilt. The wear rate is proportional to the g-force. At low speeds, the grit is ground into the metal at a moderate force, but doubling the bowl speed causes four times the wear rate. It cuts the service life to 1/4 of what it would be, and considering down time, easily increases the maintenance cost five fold.

In addition, as the centrifuge wears, it loses metal. It unfortunately doesn’t lose it uniformly, and as it wears, it goes out of balance. As I discussed previously, imbalance means premature failure through excessive vibration.

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