Our Initial Small-Scale Testing with RCD Seal Operating Conditions
Over the years, Kalsi Engineering has performed many tests directed at rotary control device (RCD) sealing. When we first came up with the concept for the now-patented floating metal backup ring, we did our initial testing in a test fixture with a 2.75” (69.85mm) shaft, so that we could get quick, economical feedback on rotary seal performance and hardware ease of assembly. Later, we developed a 10.50” test fixture, to perform full-scale tests of RCD seals with and without floating backup rings. This web page describes the initial 2.750” testing, which simulated the operating conditions of a high-pressure RCD seal in a lubricant overpressure-type RCD. In this type of RCD, the seal lubricant is maintained at a pressure that is greater than the pressure of the drilling fluid.
One difficulty faced in high-pressure RCD sealing is the high runout and lateral displacement of the rotating mandrel. Ordinarily, this requires that the housing-to-mandrel extrusion gap clearance be large, to prevent destructive, heavily loaded metal-to-metal contact at the extrusion gap. The large extrusion gap clearance is detrimental to high-pressure seal performance.
The floating backup ring was developed to follow shaft runout and lateral displacement while providing a small, dimensionally stable extrusion gap clearance. The 2.750” tests were performed with an intentional shaft runout of 0.010” (0.25mm). The rotary seals where installed in a floating backup ring having a clearance that is achievable in full-size equipment, considering factors such as manufacturing tolerances, pressure-induced deformation, and differential thermal expansion — 0.008” (0.02mm) total diametric clearance. Two rotary tests were performed, and each test exposed two PN 682-5-303 Kalsi Seal-brand Plastic Lined™ rotary shaft seals to a lubricant pressure of 3,000 psi (20.68 MPa) and a rotary speed of 750 rpm, yielding a surface speed of 540 sfpm. This surface speed is equivalent to 200 rpm on a 10.375” (263.53mm) shaft, however, at 750 rpm, the test seals were exposed to 3.75-times more runout cycles. The seal lubricant, which was was an ISO 150 VG synthetic hydrocarbon lubricant, was maintained at 200°F (93.33°C) by a circulating coolant.
One 3,000 psi test was scheduled for and successfully reached 200 hours, and the other was scheduled for and successfully reached 300 hours. These test durations were selected because they meet or exceed the 100-hour minimum and 200-hour maximum duration specified by API 16RCD for RCD seal testing. The Kalsi Seal-brand rotary shaft seals survived in both tests, with varying degrees of damage, despite being exposed to 3.75-times more runout cycles than a 10.375” diameter RCD seal operating at 200 rpm. The seals clearly benefited from the small extrusion gap provided by the floating metal backup ring.
These initial 2.750” tests quickly demonstrated that the Plastic Lined Kalsi Seal™, combined with the floating metal backup ring, represented a new benchmark in high-pressure RCD sealing technology. Since this initial success, we have developed much simpler, and much more dimensionally stable floating backup rings, and we have tested them at full-scale size. This seal and backup ring technology also has application in other types of equipment, such as high-pressure cement swivels, hydraulic swivels, and mud swivels.
For information on implementing this high-pressure rotary seal technology, see the Kalsi Seals Handbook™, call us at 281-240-6500, or contact us by e-mail. Also, see the OTC-26899-MS technical paper. For available styles and sizes of RCD seals, see our shaft seal catalog.
This video documents a 3,000 psi (20.68 MPa), 750 rpm test of a 2.75” (69.85mm) high-pressure rotary seal that was performed with 0.010” (0.25mm) dynamic runout (TIR) for 300 hours. The purpose of the test was to economically evaluate a new rotary seal design in conditions that simulated an oilfield rotary control device (RCD).
This video documents the disassembly of the 3,000 psi, 300-hour high pressure rotary seal test. The Kalsi-brand rotary seals survived this grueling test, which exposed the seals to 0.010” runout (TIR) at 750 rpm.