Question 1

How do I choose between a soft gasket (like CNA) and a metallic gasket?

Accepted Answer

The choice depends on flange conditions and service parameters. Soft gaskets (Compressed Non-Asbestos, Graphite) are excellent for flanges with slight imperfections as they conform easily. They are suitable for a wide range of temperatures and pressures common in process plants. Metallic gaskets (Spiral Wound, RTJ) are required for very high pressures (Class 900 and above), extreme temperatures, or where creep relaxation of soft materials would be a concern. They require higher bolt loads and very flat, smooth flange surfaces. Kaxite Sealing application engineers can perform a detailed assessment to recommend the optimal type.

Question 2

What is gasket "blow-out" and how can it be prevented?

Accepted Answer

Blow-out occurs when internal pressure forces the gasket material out of the flange gap, causing sudden failure. It is prevented by ensuring the gasket has sufficient mechanical strength and density for the application pressure. Using a properly designed gasket with adequate thickness, selecting a material with high tensile strength (like our reinforced CNA grades), and most critically, applying the correct bolt torque to generate enough compressive force to counteract the internal pressure are key. Kaxite provides specific torque recommendations for our products.

Question 3

Can I re-use a gasket after disassembling a connection?

Accepted Answer

It is generally not recommended to re-use gaskets, especially compressed non-asbestos, graphite, or PTFE gaskets. These materials undergo permanent deformation (compression set) during initial installation to conform to the flange faces. Upon removal, they lose their sealing resilience and will likely leak if re-installed. Metal gaskets, like some RTJ types, may be re-usable if they are undamaged, but this should be evaluated on a case-by-case basis and per the original equipment manufacturer's guidelines. For guaranteed leak-free performance, Kaxite Sealing always advises installing a new gasket.

Question 4

What is the significance of the "gasket factor (m) and seating stress (y)" values?

Accepted Answer

These are empirical constants used in traditional flange design calculations (like ASME BPVC Section VIII, Appendix 2). The 'y' factor is the minimum seating stress needed to initially compress the gasket onto the flange surfaces. The 'm' factor (maintenance factor) is a multiplier used to calculate the required bolt load to maintain a seal under operating pressure. While modern gasket standards like EN 1591 use more advanced methods, these factors remain important for material comparison and legacy designs. Kaxite Sealing provides certified m and y values for our gasket materials based on rigorous testing per ASTM F36 and other standards.

Question 5

How does temperature affect gasket performance and selection?

Accepted Answer

Temperature is a primary driver. It affects the gasket material's physical properties: elastomers harden or degrade, binders in composite materials can carbonize, and thermal cycling can cause fatigue. Key considerations include the maximum continuous operating temperature, thermal cycling frequency, and the temperature gradient across the flange. For high temperatures, materials like flexible graphite, PTFE, and specific metals are chosen. For cryogenic services, materials must resist embrittlement; PTFE and certain graphite grades are effective. Always consult the manufacturer's temperature limits—Kaxite Sealing provides detailed, tested temperature ratings for all our products.

Question 6

Why is surface finish of the flange important?

Accepted Answer

The flange surface finish (often measured in Ra micro-inches or microns) determines how well the gasket can conform and seal. A very rough surface requires a softer, more conformable gasket to fill the valleys. A very smooth surface may not provide enough "grip" and could allow gasket slippage under pressure. An optimal finish (typically 125-250 Ra µin or 3.2-6.3 µm for soft gaskets) provides a balance. Serrated (phonographic) finishes are common. For metal gaskets, a much smoother finish is required. Matching the gasket type to the existing flange surface is crucial, and Kaxite can advise on compatibility.

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