What type of gasket is normally used on a flange valve in a High-Pressure/ High-Temperature line?

• A. Graphite sheet gasket
• B. O-ring
• C. Flexitallic Spiral Wound
• D. Ring joint

Answer: (C)

In high-pressure, high-temperature piping, you need a gasket that can seal reliably across rigid flange faces while tolerating minor surface imperfections and maintaining a tight seal as conditions shift. A spiral-wound gasket fits that need perfectly: it combines a metal winding with a softer filler, which gives it real strength to withstand high pressures and temperatures and the ability to conform to flange gaps or irregularities. The outer and inner rings on many spiral-wound designs help keep the gasket in place and protect the sealing material, making it a versatile choice for raised-face or flat-face flange joints common in HP/HT lines like those with valves.

Other options don’t match as well in typical HP/HT flange service. A graphite sheet gasket can handle heat but may not provide enough resilience under high pressures or thermal cycling. An O-ring is great for equipment seals but isn’t suited to flange-gap sealing between two bolted surfaces. Ring joints are used with specific RTJ flanges and are common in very high-pressure service, but they require the appropriate flange type and aren’t as universal for standard flange valves as spiral-wound gaskets.