What Is BX Ring Gasket?

A BX ring gasket is a solid metal pressure-energized sealing ring designed for API 6BX flanges on wellhead equipment, Christmas trees, and high-pressure upstream connections rated from 5,000 to 20,000 psi. The BX ring features an octagonal-like cross-section with a radial pressure-balance hole that allows internal pressure to act on the gasket, expanding it into the groove and increasing seal contact stress as pressure rises.

Feature	Specification
Type	Solid metallic ring gasket
Standard	API 6A (Specification for Wellhead and Christmas Tree Equipment)
Flange type	API 6BX only (not interchangeable with R or RX grooves)
Pressure range	5,000-20,000 psi working pressure
Pressure energization	Yes; radial hole transmits bore pressure to expand ring
Sealing mechanism	Metal-to-metal contact by elastic/plastic deformation
Reusability	No (single use)

How BX Gaskets Seal

The BX ring seats in a machined groove in the API 6BX flange. Initial bolt load compresses the ring, creating a metal-to-metal seal on the groove surfaces. The radial pressure-balance hole connects the bore pressure to the inside of the ring. As pressure increases, it pushes the ring outward against the groove walls, intensifying the seal.

This self-energizing mechanism gives BX gaskets a critical advantage in upstream service where pressure surges, water hammer, and rapid pressure changes are common. Conventional R-type RTJ gaskets rely only on the initial bolt load and can lose seal contact if bolt relaxation or thermal movement reduces clamping force.

BX Ring Dimensions (API 6A)

Ring Number	Bore Size (in)	Pressure Rating (psi)	OD (mm)	ID (mm)	Height (mm)
BX-150	1-13/16	5,000	52.37	38.10	15.88
BX-151	2-1/16	5,000	60.32	44.45	15.88
BX-152	2-1/16	10,000-20,000	60.32	44.45	15.88
BX-153	2-9/16	5,000	73.02	55.56	17.48
BX-154	2-9/16	10,000-20,000	73.02	55.56	17.48
BX-156	3-1/8	5,000-20,000	87.31	66.68	19.05
BX-158	3-1/8	15,000-20,000	87.31	66.68	19.05
BX-160	4-1/16	5,000-20,000	111.12	88.90	22.23

BX ring numbers do not correspond to ASME B16.20 R-ring numbers. A BX-152 and R-24 are completely different gaskets even though both can apply to 2” nominal connections.

Material Requirements

Material	Hardness (max)	Service
AISI 4130 (low-alloy steel)	22 HRc	Standard wellhead service
AISI 410 SS	23 HRc	Mild corrosion resistance
Incoloy 825	25 HRc	Sour gas (H2S) per NACE MR0175
Inconel 625	30 HRc	Subsea, severe corrosion
Inconel 718	35 HRc	Ultra-high-pressure, high-temperature

The BX gasket must be softer than the API 6BX flange groove material. Hardness differential of at least 5 HRc is recommended to ensure the ring deforms into the groove without damaging the flange.

BX vs RX Ring Gaskets

Feature	BX	RX
Groove compatibility	BX grooves only	R and RX grooves
Max pressure	20,000 psi	15,000 psi
Pressure hole	Yes (radial)	No (hollow body expands)
Flange standard	API 6BX	API 6B
Use case	Highest-pressure wellhead service	Mid-range upstream, backward-compatible

Pro Tip

BX ring gaskets must be stored with anti-corrosion coating and protective caps. A single scratch, dent, or corrosion pit on the sealing surface can cause a leak at 20,000 psi. Inspect every ring visually and with hardness verification before installation. Reject any ring with visible surface damage.

BX rings require high-strength stud bolts and controlled tensioning procedures specified by the wellhead equipment manufacturer.

Read the full guide to gasket selection