Graphite Filler Class 150 ASME B16.20 Flange Seal Spiral Wound Gasket

A flange joint is only as reliable as the gasket squeezed between its faces. On Class 150 lines that see temperature swings and corrosive media, the graphite filler spiral wound gasket built to ASME B16.20 is the standard choice, and it pays to know how the ring is made before it replaces ordinary flange gaskets.

What a Spiral Wound Gasket Is

A spiral wound gasket is a semi-metallic seal: plies of metal strip and flexible graphite filler are wound together into a ring. The metal strip carries the bolt load and keeps the ring round, while the graphite does the sealing. Inner and outer guide rings hold the winding in place and centre the gasket in the joint.

These gaskets sit between the faces of pipe flanges, and ASME B16.20 covers metallic gaskets for flanged joints, spiral wound designs included. A Class 150 gasket made to that standard is dimensionally matched to its joint, so size and thickness are settled before the bolts are tightened.

Table 1. Main elements of a graphite filler Class 150 spiral wound gasket built to ASME B16.20.

Construction and Service Advantages

Four properties explain why this gasket is specified on critical joints.

• Sealing under changing load — the wound construction is elastic, so the seal holds through pressure and temperature fluctuations, and the graphite conforms to minor face irregularities.
• Heat resistance — graphite filler works at elevated service temperature and draws heat away from the sealing line, which suits steam and hot process media.
• Chemical resistance — flexible graphite stands up to a broad range of corrosive fluids and aggressive chemicals, so the seal survives harsh media.
• Wide size range — gaskets are wound in many sizes and configurations, from standard pipe sizes to large equipment nozzles.

The ring is elastic rather than rigid, so bolt load matters: too little and the graphite never seats, too much and the winding is crushed.

Where Class 150 Graphite Spiral Wound Gaskets Are Used

One construction covers three fields.

• Oil and gas — pumps, valves and compressors, where pipeline flanges must stay leak-free under vibration and pressure surges.
• Chemical processing — equipment handling corrosive substances, where a leak is both a safety hazard and an environmental problem.
• Power generation — steam turbines, boilers and heat exchangers, where the seal must hold at high temperature and across pressure differentials.

Selection comes down to medium, temperature and the pressure class of the joint: match the gasket to the flange class and confirm the filler suits the fluid before installation.

Frequently Asked Questions

What does ASME B16.20 specify for this gasket?

ASME B16.20 covers metallic gaskets for flanged joints, spiral wound designs included. A gasket made to that standard follows defined dimensions, materials and tolerances, so it fits a Class 150 joint as intended.

Why is graphite used as the filler?

Graphite combines compressibility, heat resistance and chemical resistance. It conforms to surface irregularities, keeps the seal at elevated temperature and tolerates corrosive media — the three demands Class 150 process joints usually face.

Can this gasket seal a damaged flange face?

No. The filler compensates for small waviness, not for gouges, erosion or corrosion pitting. Refinish or replace damaged faces first, otherwise the joint will leak whatever gasket is fitted.

How should a spiral wound gasket be installed?

Centre it on the bolts, bring the flanges together evenly and tighten the bolts in a cross pattern in several passes to the target bolt load. Do not reuse a gasket that has already been compressed: it takes a permanent set and will not seal again.