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Improved Elastomers are Reducing Downtime for Floating Drill Rigs
2014-03-03
The dynamic elastomeric seals, or packers, that contain drilling mud within the risers of floating rigs experience a great deal of abrasion during their service life. Packers interface between the inner and outer barrels of the telescopic joints (TJ) that accommodate vertical motion from vessel heave. The packers are subjected to constant pneumatic or hydraulic pressure to maintain their seal.
When using TJ packers made of standard nitriles, which wear very quickly, rigs can experience frequent downtime for replacement of leaking seals. Urethane packers are an alternative that provide improved wear-resistance, but their stiffness requires higher actuation pressures to seal, which in turn can require challenging and expensive adjustments to the rig. Urethanes are also susceptible to hydrolysis when exposed to water, which results in a loss of mechanical properties.
In response to these challenges, we developed a TJ packer made of a wear-resistant nitrile, as well as, one made of a soft wear-resistant nitrile (which is suitable for applications with a lower targeted stiffness). Both exhibit much less wear than other nitriles in abrasive environments.
Tests showed:
- Wear-resistant nitrile samples tested on an abrader machine lost 23 to 31 times less materialthan a standard nitrile.
- After swell testing, polyurethane retained only about 10 to 15 percent of its original tensile strength while our wear-resistant nitrile and soft wear-resistant nitrile retained about 90 percent of their tensile strength.
- A packer made of our wear-resistant nitrile was tested on a full-scale laboratory replica of a telescopic joint and following only 10% of the qualification testing, ours did not lose any mass or thickness, while the standard nitrile packer lost 0.46 pounds and had a maximum decrease in thickness of seven percent.
- Wear-resistant nitriles were field-tested and results demonstrated the wear-resistant nitrile packer lasted 20 times longer than a standard nitrile packer.
The new elastomer performed so well that in one field test special accommodations were made to have it reinstalled on a rig where a standard nitrile packer had begun to leak after only four days. The LORD wear-resistant packer, which had already seen 21 days of service before its TJ assembly was sent to shore for unrelated maintenance, was flown back to the rig. It then provided an additional 62 days of service and based on its condition at that time —it had lost only 25 percent of its thickness—the wear-resistant packer could have been returned to service again.
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