Last updated: April 2026
Spiral wound gaskets are the default sealing element on virtually every flange in an oil refinery. From the crude unit at the front end to the hydrocracker and reformer at the back, every raised-face flange between Class 150 and Class 2500 is sealed with a spiral wound gasket built to ASME B16.20 / API 601. The right configuration — winding alloy, filler, and inner-ring choice — varies by unit and service.
This page maps the common refinery units to the spiral wound gasket spec we ship most often for each. Use it as a starting point when specifying a new flange or troubleshooting a recurring leak.
Crude Distillation & Vacuum Unit
Atmospheric and vacuum columns operate at moderate pressure but high temperature (350–400°C at the bottoms). Crude is corrosive — chlorides, naphthenic acids, sulphur. Spiral wound gaskets here typically run:
- Centring ring: 316SS (chloride resistance).
- Winding: 316L stainless (or 321 in higher-temp service).
- Filler: flexible graphite, oxidation-inhibited grade.
- Inner ring: on Class 600+ headers; optional below.
Hot vacuum-tower side draws and the bottom of the crude column see naphthenic-acid attack; switch to Inconel 825 winding for known-aggressive crudes.
Hydroprocessing — Hydrotreater & Hydrocracker
The hardest service in the refinery. High-pressure hydrogen at 350–450°C with sulphur and ammonia in the feed. 316SS is borderline for creep at these temperatures and prone to hydrogen embrittlement.
- Centring & inner ring: Inconel 625 or 825.
- Winding: Inconel 625 for hydrocracker effluent; 321SS acceptable for cooler hydrotreater service.
- Filler: oxidation-inhibited flexible graphite, low chloride.
- Inner ring: mandatory.
See the Class 900 Inconel 625 spiral wound configuration for the typical hydrocracker effluent flange spec.
Catalytic Reformer & Cat Cracker (FCC)
Reformer reactor flanges run at 480–540°C with high-purity hydrogen. FCC regenerator flanges run hotter (700°C+) in oxidising atmospheres — graphite oxidises rapidly here.
- Reformer reactors: Inconel 625 winding, oxidation-inhibited graphite filler, Inconel inner ring.
- FCC regenerator: mica-filled spiral wound (graphite would burn out). Carbon-steel or 316SS centring acceptable; 321SS winding.
- FCC flue-gas slide valve: ceramic-filled or mica-filled depending on temperature.
Heat Exchangers & Coolers
Shell-and-tube heat-exchanger header flanges are the highest-volume gasket consumer in a refinery. Thermal cycling is the primary failure mode: bolt preload drops as the joint heats and cools, the gasket loses seal, hydrocarbons leak.
- Centring & inner ring: 316SS (matches winding for thermal expansion).
- Winding: 316L stainless.
- Filler: flexible graphite (best recovery under cyclic load).
- Inner ring: mandatory at Class 600+; strongly recommended at Class 300 for cyclic service.
Hot re-torque after first thermal cycle is critical here — see our PCC-1 bolt-up guide.
Steam & Condensate Systems
HP steam (60 bar+, 500°C+) is the cleanest hot service in the refinery — no chlorides, no sulphur — but the temperature and thermal cycling are unforgiving on bolt preload.
- Centring ring: carbon steel (zinc-plated) or 316SS depending on insulation and corrosion environment.
- Winding: 304SS standard; 316L for higher-spec.
- Filler: flexible graphite.
- Inner ring: mandatory at Class 600+ steam.
Sour Service (H₂S Containing)
Sour-service piping per NACE MR0175 / ISO 15156 — amine units, sour-water strippers, sour gas separators. Standard 316SS is at the limit of acceptable hardness for sour duty; Inconel is preferred at higher temperatures.
- Centring & inner ring: 316L or Inconel 625 (NACE-compliant heat treatment).
- Winding: 316L (low-carbon to control hardness) or Inconel 625.
- Filler: flexible graphite, low chloride.
- Inner ring: recommended at all classes — H₂S degrades the filler if in contact with the process.
Common Refinery Spiral Wound Failures
- Standard graphite filler in oxidising service above 450°C — slow filler oxidation, residual stress drops below operating m factor, joint weeps. Switch to oxidation-inhibited graphite or mica.
- 316SS winding in hot hydrogen service — creep relaxation; preload lost. Switch to Inconel 625.
- No inner ring on Class 600+ heat exchanger — filler erosion at cycling temperatures. Always specify inner ring.
- No hot re-torque after first thermal cycle — initial preload lost to creep, joint never reaches operating residual stress.
- Chloride contamination from standard graphite on hot stainless flanges — stress-corrosion cracking. Specify nuclear-grade or low-chloride filler (≤50 ppm Cl).
Frequently Asked Questions
316SS centring ring, 316L stainless winding, flexible graphite filler, with an inner ring on Class 600 and above. This covers the vast majority of crude, hydrotreater, heat-exchanger, and steam service across an Australian refinery. Switch to Inconel 625 winding for hot hydroprocessing or hydrocracker effluent.
Switch to mica when continuous service exceeds 450°C in oxidising atmospheres (typically FCC regenerator headers, flue-gas ducts, exhaust manifolds). Standard graphite oxidises slowly above this threshold — the filler loses mass, the seal loses preload. Mica handles 800°C continuous and 1000°C peak.
316L stainless is acceptable for many sour-gas duties per NACE MR0175 / ISO 15156, provided hardness is controlled (typically below 22 HRC) and the heat treatment is correct. For higher-temperature sour service or higher H₂S partial pressures, switch to Inconel 625 or Hastelloy C-276 winding and matching inner ring.
Three usual culprits: no inner ring (filler erosion under cycling), no hot re-torque after first warm-up (creep relaxation lost preload that never came back), or wrong filler (PTFE above 200°C creeps under cyclic load). Specify a graphite-filled spiral wound with inner ring, follow ASME PCC-1 bolt-up, and re-torque hot after 24 hours at temperature.
For hot stainless flanges (above ~150°C) where standard graphite filler is in contact with the flange face, yes — leached chlorides can initiate stress-corrosion cracking on austenitic stainless. Specify nuclear-grade or low-chloride flexible graphite (≤50 ppm Cl) for hot stainless service. At ambient or near-ambient temperatures the risk is negligible.
Related
- Spiral wound gaskets — full configuration range
- Filler selection guide
- Bolt-up to ASME PCC-1
- Custom spiral wound — non-standard sizes
Sources
- API 601 — Metallic Gaskets for Raised-Face Pipe Flanges
- NACE MR0175 / ISO 15156 — Materials for Use in H₂S-Containing Environments
- API RP 582 — Welding Guidelines for the Chemical, Oil, and Gas Industries