Oil & Gas Sealing: NACE MR0175, API 6A/6D Standards & Material Selection

Author: Site Editor Publish Time: 2026-05-25 Origin: Site

Oil & Gas Sealing Environment

Oil and gas sealing is one of the most demanding environments in industrial sealing. Seals must withstand high pressures, extreme temperatures, aggressive chemicals, and often sour gas (H₂S) exposure. Getting the material and standard wrong can result in serious safety incidents.

Key Standards for Oil & Gas Seals

Standard	Scope
NACE MR0175 / ISO 15156	Elastomers for H₂S-containing environments in petroleum production
API 6A	Wellhead and Christmas tree equipment — pressure ratings, material classes
API 6D	Pipeline valves and flanged connections
API 6A PSL 3G	Product specification level for high-pressure/high-temperature wellhead
ISO 14310	Downhole packers and bridge plugs — elastomer requirements

NACE MR0175 / ISO 15156 — H₂S Environment

Any seal used in an H₂S-containing environment must be certified compliant with NACE MR0175 (or the newer ISO 15156 series). This standard restricts which elastomer formulations can be used.

FKM: Limited use in H₂S — only certain grades approved (check ISO 15156-2)
Aflas® (FEPM): Excellent H₂S resistance — widely used in sour gas wells
NBR: Not approved for H₂S service above certain partial pressures
FFKM: Highest H₂S resistance — for critical sour gas applications

API 6A Material Classes for Wellhead Seals

Material Class	Temperature	Elastomer Suitability
AA	−18°C to +121°C	Standard NBR, FKM
BB, CC	−18°C to +121°C	Acid-resistant FKM, Aflas®
DD, EE, FF	−46°C to +180°C	Special FKM, Aflas®, FFKM

Application Zones & Material Selection

Downhole drilling: High temp (up to +200°C), drilling mud, H₂S possible → Aflas® or FFKM
Wellhead (Christmas tree): High pressure, thermal cycling, sour gas → Aflas® or special FKM
Subsea (BOP, manifolds): Deepwater pressure, seawater exposure, H₂S → FFKM for high-critical
Refinery processing: Hydrocarbon fluids, steam, acids → FKM or Aflas®
Pipeline (API 6D): Hydrocarbon transport, various temperatures → FKM or Aflas®

Seal Types for Oil & Gas

FKM/Aflas® O-rings: API 6A wellhead and valve flange seals
Metal C-ring seals: For high-pressure (10,000+ psi) wellhead barriers
Elastomer energised metal seals: For subsea Christmas tree junctions
Packers and downhole seals: Elastomer elements for completion tools

Testing Requirements

Material certification per lot (traceability from base polymer to finished seal)
NACE MR0175 compliance documentation for H₂S applications
API 6A PSL verification for wellhead equipment suppliers
Third-party test reports for new part qualifications (dimensional, material, pressure)

Anlintech supplies FKM and Aflas® seals for oil and gas applications with NACE MR0175 documentation. Contact us for material recommendations and technical compliance documentation.