C-P Systems
What Is a Spiral Wound Gasket? | Piping Engineering Glossary
What Is a Spiral Wound Gasket?
In piping engineering and process engineering, a spiral wound gasket is a semi-metallic gasket made by winding a V-shaped metal strip together with a soft filler material, such as flexible graphite or PTFE, into a tight spiral. The metal provides strength and resilience, while the filler flows into surface imperfections to create a seal. Spiral wound gaskets are among the most widely used gaskets in process piping.
Construction of a Spiral Wound Gasket
A typical spiral wound gasket has three parts. The sealing element is the wound spiral of metal and filler. An outer ring, usually carbon steel, centers the gasket inside the bolt circle and acts as a compression stop to prevent over-compression. An inner ring, often stainless steel, protects the windings from the process fluid, prevents them from buckling inward, and is required in many services and sizes.
Spiral wound gaskets are usually installed on raised face flange joints and are made to match the flange size and flange pressure class under standards such as ASME B16.20. The winding metal and filler are chosen for temperature, pressure, and chemical compatibility.
Applications
General Process Piping
Spiral wound gaskets are a standard choice for Class 150 through Class 2500 flanged joints in hydrocarbon, steam, and many chemical services. They are often the default gasket in refinery and petrochemical piping specifications.
High-Temperature and Cyclic Service
Their resilience lets them recover as flanges move during temperature changes, which helps maintain gasket compression through startups and shutdowns.
Heat Exchangers and Vessels
Special shapes with pass partition bars are used on heat exchanger girth flanges and channel covers, where flat sheet gaskets may not hold up.
Benefits
Wide Operating Range
Different winding and filler combinations cover temperatures from cryogenic to well above 500°C. One gasket type can serve most of a plant.
Resilience
The spiral acts like a spring, helping the joint stay sealed when bolt load or temperature changes. This improves reliability in cyclic service.
Blowout Resistance
The metal windings and outer ring make spiral wound gaskets much more resistant to blowout than soft sheet gaskets. This adds a safety margin in fire-prone and high-pressure services.
Limitations
Needs a Suitable Flange Finish
Performance depends on the correct flange face finish, typically a serrated finish within a specified roughness range. Damaged or very smooth faces reduce sealing reliability.
Sensitive to Assembly
Uneven or excessive bolt torque can buckle the windings and cause flange leakage. Controlled tightening procedures are essential.
Single Use
Once compressed, a spiral wound gasket cannot recover its original shape, so it must be replaced whenever the joint is opened.
FAQ
What does the outer ring do?
It centers the gasket within the bolts, limits compression so the windings are not crushed, and adds radial strength against blowout.
When is an inner ring required?
Inner rings are required for PTFE-filled gaskets and for many larger sizes and higher pressure classes, and they are often specified for vacuum, corrosive, or high-temperature service.
Can spiral wound gaskets be reused?
No. They are designed for a single compression cycle and should be replaced every time the flanged connection is opened.
What do the color markings mean?
Color codes on the outer ring edge identify the winding metal and filler material, helping crews confirm they have the right gasket before tightening the stud bolts.
About C-P Systems
SETTING THE STANDARD FOR CHEMICAL ENGINEERING FIRMS EVERYWHERE
Through unmatched professionalism, knowledge and experience, we set the industry bar for chemical engineering firms. With decades of chemical plant engineering and piping design experience, our team of licensed engineers can handle any project scope.