Page 193 - Well Control for Completions and Interventions

Well Control Surface Equipment 185

Figure 4.32 “R” type ring gasket.

deforms to form a seal (coining) without deforming the ring groove in
the flange face. A ring gasket should never be reused.

4.13.2.1 “R” ring gasket
The type “R” ring gasket seals along a small band of contact on both the
OD and ID of the gasket. It is not energized by internal pressure. These
gaskets are either oval or octagonal in cross-section. Since the “R” gasket
does not allow face-to-face contact between the flange face, any external
loads are transferred through the sealing surface to the ring. Vibration and
external loads can cause small bands of contact between the ring and the
groove to deform plastically, so that the joint may develop a leak unless the
flange bolting is periodically tightened. Standard procedure with type “R”
joints in the BOP stack is to tighten the flange bolting weekly (Fig. 4.32).

4.13.2.2 “RX” pressure energized ring gasket
Originally a Cameron development, the “RX” gasket is now recognized
by the API. Octagonal in cross-section, it is energized by well pressure
along a band of contact between the groove in the flange and the OD of
the ring. Since the gasket is slightly larger in diameter than the groove,
tightening the flange bolts compresses the ring and creates an initial seal
that is fully energized by internal pressure. The “RX” gasket does not
allow face-to-face contact between the flange face, so any external load is
transferred through the sealing surface to the ring. However, as the gasket
has a large load-bearing surface on its inside diameter, loads are transmitted
without excessive plastic deformation of the sealing surface (Fig. 4.33).