Exploring the Versatility and Reliability of API 6A RX 31 Joint Gaskets

API 6A RX 31 joint gaskets are pressure-energized metal ring gaskets built to the API 6A standard: the ring sits in machined grooves on two flange faces, and sealing force grows with line pressure. Alongside the flange gaskets used on general piping, the RX type is the default on wellheads, Christmas trees and other high-pressure oilfield equipment.

What the RX 31 Design Delivers

The RX 31 designation identifies the ring size and profile within the API 6A RX family. The rings are supplied in carbon steel (CS) to a maximum hardness of 120 HB — softer than the flange groove faces, so the seal forms on the ring without damaging the flange. Metal-to-metal contact keeps the joint tight at extreme temperatures and pressures, and the pressure-energized profile means the seal improves as service pressure rises.

• Pressure-energized ring profile: sealing force increases with line pressure instead of relaxing.
• Metal-to-metal contact for extreme temperature and pressure service.
• Carbon steel (CS) rings to API 6A, maximum hardness 120 HB.
• Standardized ring numbers, including RX 31, matched to API 6A flange grooves.

Where RX 31 Gaskets Work

Offshore drilling is the defining environment: extreme temperatures, high pressure and seawater corrosion act at the same time. RX 31 gaskets are used in blowout preventers, wellhead connectors and subsea equipment, where durability and corrosion resistance decide whether the seal survives.

Refineries use them everywhere a flanged joint must stay leak-free: connecting pipeline flanges in pipeline systems, on gate, ball and globe valves, heat exchangers, distillation columns and reactors. The same metal-to-metal seal handles sulfur compounds, alkalis and other aggressive media, plus the thermal swings of startup, shutdown and process changes.

Chemical and petrochemical plants add highly corrosive chemicals to the picture: reactors, piping systems, pressure vessels, boilers and heat exchangers all rely on tight flanged joints. Leak-free connections cut product loss, avoid unplanned downtime and keep personnel safe.

Table 1. Typical service locations for API 6A RX 31 joint gaskets and the duty each one imposes on the seal.

Sealing Performance in Aggressive Media and Thermal Cycling

Aggressive media — acids, alkalis, sulfur compounds — degrade soft sealing materials over time and start leaks that look like minor seepage until they are not. The metal-to-metal RX contact avoids that ageing mechanism; where the chemistry is unusually severe, the ring material should be checked against the medium before selection.

Temperature fluctuation is the other hidden load. During startup, shutdown and process changes the joint expands and contracts; a pressure-energized ring follows those movements better than an elastomeric seal, so the connection stays leak-tight and production runs without interruption. In practice this shows up as lower product loss, fewer repair shutdowns and a longer interval between gasket changes.

Frequently Asked Questions

What does the RX designation mean on an API 6A gasket?

RX marks the pressure-energized ring profile: the ring fits API 6A flange grooves and its sealing force grows with line pressure, unlike flat gaskets.

What material is the RX 31 ring and what hardness limit applies?

Carbon steel (CS) to API 6A, supplied to a maximum hardness of 120 HB so the ring forms the seal without damaging the flange groove faces.

Where are RX 31 gaskets used offshore?

In blowout preventers, wellhead connectors and subsea equipment, where high pressure and seawater corrosion act at the same time.

Can the ring material handle aggressive refinery chemicals?

The metal-to-metal seal copes with typical refinery media such as sulfur compounds and alkalis. For strong acids or unusual chemistry, verify the ring material against the medium before specifying.