What should the AARH finish be for a spiral wound gasket?

The recommended Arithmetic Average Rough Height (AARH) finish is 125-250 AARH.

Gaskets and Flange Face interview questions with answers covering Proper selection of gaskets and flange face finishes is critical to preventing catastrophic leaks in refineries, power plants, and chemical processing facilities.

Gaskets and Flange Face Finishes in Piping

Q: Which type of gasket is recommended for high-temperature applications?

The Spiral Wound Metallic Gasket is highly recommended for high-temperature and high-pressure services.

A piping system is truly only as strong as its weakest joint. Proper selection of gaskets and flange face finishes is critical to preventing catastrophic leaks in refineries, power plants, and chemical processing facilities. In this comprehensive guide, we dive deep into the specific types of gaskets, winding material selection, and the exact serration finishes required to guarantee secure, long-lasting flange connections.

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Gasket Types and Selection

Q1. How are gaskets classified based on their physical construction?

Gaskets are generally classified into the following common types based on how they are constructed:

Full Face Gaskets
Spiral Wound Metallic Gaskets
Ring Type Joint (RTJ) Gaskets
Metal Jacketed Gaskets
Inside Bolt Circle Gaskets

Q2. Which type of gasket is highly recommended for high-temperature and high-pressure applications?

The Spiral Wound Metallic Gasket is the industry standard and highly recommended for extreme temperature and pressure services due to its resilience and recovery properties.

Q3. What are the specific criteria for selecting the material of a spiral wound gasket?

The selection of the internal winding material depends on three crucial factors:

The corrosive nature and concentration of the process fluid.
The peak operating temperature of the fluid.
The relative cost of alternative winding materials.

Flange Face Serration & Finishes

Q4. What are the types of serrated finishes provided on a flange face?

Flange serrations grip the gasket to prevent blow-outs. They can be either:

Concentric Serrations: Distinct, separate circular grooves.
Spiral (Phonographic) Serrations: One continuous groove spiraling outward.

Q5. How is the serration on flanges technically specified?

Serration roughness is formally specified by its Arithmetic Average Rough Height (AARH).

Q6. What should the AARH finish be when using a spiral wound gasket?

To ensure a proper bite into the gasket material without damaging it, the recommended finish on the flange face for a spiral wound gasket is 125–250 AARH.

Conclusion

Selecting the optimal spiral wound gasket and verifying the correct AARH serration finish guarantees a reliable, leak-free industrial environment. Paying meticulous attention to these seemingly small sealing details prevents costly downtime and significantly enhances overall plant safety.

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Gaskets & Flange Face Finishes Quiz

Test your practical knowledge of gasket selection, flange serrations, and sealing principles. Use the Next and Back buttons to navigate.

Question 1 of 10

1. You are selecting a gasket for a high-temperature, high-pressure superheated steam line. Which type of gasket is highly recommended by industry standards for this severe service?

Full Face Elastomer Gasket Spiral Wound Metallic Gasket Non-metallic Teflon (PTFE) Gasket Inside Bolt Circle Asbestos Gasket

2. A maintenance engineer requests a flat face (FF) flange for a brittle cast iron pump casing. What type of gasket must be used with this flat face flange to prevent cracking the casing when the bolts are tightened?

Spiral Wound Metallic Ring Type Joint (RTJ) Full Face Gasket Metal Jacketed Gasket

3. When specifying the internal winding material for a spiral wound gasket on a new pipeline, what three primary criteria must dictate your selection?

Flange rating, pipe schedule, and bolt torque Fluid corrosiveness, operating temperature, and relative cost Outer ring color, inner ring thickness, and AARH finish Pipe diameter, gasket manufacturer, and testing pressure

4. To ensure a gasket does not blow out under pressure, flange faces are machined with a specific roughness to “bite” into the gasket. How is this roughness technically specified on piping drawings?

PSI (Pounds per Square Inch) BHN (Brinell Hardness Number) AARH (Arithmetic Average Rough Height) NB (Nominal Bore)

5. A contractor is preparing the raised face flanges for the installation of Spiral Wound Gaskets. What is the recommended AARH finish range that the contractor must achieve on the flange faces?

32 – 63 AARH 125 – 250 AARH 250 – 500 AARH Perfectly smooth (0 AARH)

6. What happens if a flange face is machined too smooth (e.g., 63 AARH) when using a standard spiral wound gasket in a high-pressure line?

The gasket creates a permanent cold-weld to the flange. The gasket cannot grip the flange properly and is highly susceptible to blow-out. The flange bolts will require double the torque to compensate. The system operates perfectly, as smoother faces always provide better seals.

7. A visual inspection of a flange face reveals a continuous, unbroken groove spiraling outward from the bore to the outside edge of the raised face. What type of serration is this?

Concentric Serration Phonographic (Spiral) Serration Cross-Hatch Serration Ring Type Joint Machining

8. You are ordering gaskets that must fit entirely within the bolt circle of a Raised Face flange, relying entirely on the bolts to keep the gasket centered during installation. What type of gasket is this?

Full Face Gasket Ring Type Joint (RTJ) Inside Bolt Circle Gasket (IBC/Ring Gasket) Metal Jacketed Gasket

9. An engineer specifies a Ring Type Joint (RTJ) flange for a Class 1500# line. What specific type of gasket must physically be paired with this RTJ flange design?

A solid metallic octagonal or oval ring gasket A spiral wound gasket with inner and outer rings A thick elastomeric full face gasket A non-asbestos flat sheet gasket

10. On a standard Spiral Wound Gasket with a solid carbon steel outer ring, what is the primary structural purpose of that outer ring?

To seal the fluid inside the pipe To center the gasket within the bolt circle and act as a compression stop To prevent the bolts from rusting To provide a surface for the piping inspector to stamp their approval

Gaskets and Flange Face Interview Questions