Atwood drilling units getting low noise, vibration mud pumps

Feb. 1, 2002
A new mud pump is being designed around a crankshaft that is fabricated from tempered steel, a departure from the traditional crankshaft made from a casting.

A new mud pump is being designed around a crankshaft that is fabricated from tempered steel, a departure from the traditional crankshaft made from a casting. As an addition to the process of building the new pump design, LeTourneau Ellis Williams Company (Lewco), the pump fabricator, plans to load test every pump manu-factured.

The central component of the pump design is a balanced forged steel crankshaft, according to Don Vogelsang, Vice President. The fabricated crankshaft is made of heat treated alloy steel rough-machined to create a raised focus to which the eccentrics are welded. The steel is heat treated to ensure hardening, and the eccentrics are machined to produce a full penetration weld. When the welds are complete, the crankshaft is stress relieved.

Next, a post-weld heat treatment is performed on the crankshaft, followed by a magnetic particle inspection. Part of the uniqueness of the crankshaft is in the way it is manufactured, the developers say. Three basket fixtures are stacked up and bolted around the crankshaft, which is made stationary to the fixture. The fixture can be moved to place the eccentrics 120 degrees apart, without having to move the crankshaft. This makes the manufacturing process exact. The fabricated design can be weld-repaired if necessary, unlike cast crankshafts, which must be replaced in the event of bearing failure.

Enhanced features

The developers contend the fabricated crankshaft reduces noise and vibration, but perhaps more significantly, the mud pump design extends bearing life, which in turn extends the life of the pump. Internal pressure-fed lubrication ensures that the bearings are exposed to less friction and wear.

Like other mud pumps on the market, the pump has a built-in, conventional splash system. When oil is in the bottom of the sump and the gear is turning, lubrication splashes on the bearings and moving parts on the power end. By placing a manifold driven by a mechanical pump inside the power end, the design ensures that the lubricant is pressure fed to all of the bearings except for the wrist pin bearing.

The pump, designed to run on 3,000 input hp, is the largest on the market. The unit provides a maximum working pressure of 7.500 psi and produces a maximum output of 1,044 gal at 100 strokes/minute.
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Steel piping force-feeds the lubrication, and piping to the crosshead slide provides additional lubrication there. An externally mounted electric pump provides lubrication from a third source as well. Triple redundancy ensures consistent lubrication, which limits wear on the bearings and lengthens the life of the pump.

Helical gearing

Lewco's mud pump uses an American Gear Manufacturing Association grade 10 gear and pinion, cut with a double-helical gear profile. This gear profile provides greater strength than the customary herringbone profile. Double-helical construction is used for both the gear and the pinion and increases the horsepower rating of the gear and pinion set. The developers say that the double-helical gear delivers more strength when running at high horsepower.

Lewco's fabricated crankshaft
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Vogelsang said, "To produce a quality product, you have to be in control of most of the manufacturing process. You can lose control by outsourcing." With its new test facility, Lewco proposes to change the accepted process. The company manufactures everything that goes into the new pump except the gears, and has built a $1 million mud pump testing facility. The facility can load test pumps up to 3,000 hp or 7,500 psi on AC or DC electric motors, Vogelsang said.

Lewco said that three of the new mud pumps were sold to Atwood Oceanics in early October. The three 2,200-hp triplex piston mud pumps and drives will be installed on Atwood's recently announced newbuild, a Keppel FELS Ltd. MOD V Enhanced B class jackup that is being built in Singapore.