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Preparing for a piping interview can feel overwhelming. Knowing the key questions and answers can make all the difference. Especially in roles involving shutdowns or maintenance, having strong knowledge of essential piping concepts improves your chances of success. Let’s explore the 20 most common piping interview questions, their answers, and some tips to help you excel.

What Are the Types of Flanges Based on Facing?

Flanges can be classified into several types depending on their facing. Here’s a rundown of the main categories:

• Flat Face (FF): Commonly used where the flange must seat against a flat surface.
• Raised Face (RF): Generally used in most piping systems for added strength.
• Tongue and Groove: These fit together like puzzle pieces and are used where alignment and sealing are critical.
• Male and Female: Similar to tongue and groove but with different profiles.
• Ring Type Joint (RTJ): Ideal for high-pressure and high-temperature systems.

RTJ flanges are selected for situations that demand durability under extreme conditions. Understanding these classifications is key when discussing flanges.

How Are Flanges Rated for Pressure and Temperature?

Flanges are categorised into classes based on their pressure-temperature rating. These include:

• Class 150
• Class 300
• Class 400 (rarely used)
• Class 600
• Class 900
• Class 1500
• Class 2500

When you see “150#,” the “#” refers to the class. This indicates both the pressure rating (in pounds) and the temperature limits of the flange. Remember, Class 400 is rarely seen in practical applications.

What Are the Types of Flanges Based on Pipe Attachment?

Depending on how a flange connects to a pipe, they are classified into several varieties:

• Slip-On Flanges: Welded both inside and outside for a secure fit.
• Socket Weld Flanges: Welded on just one side, typically used for smaller pipelines.
• Threaded Flanges (Screwed Flanges): No welding required, ideal where welding is impractical.
• Lap Joint Flanges: Used with a stub end, where the flange is not welded but remains loose.
• Blind Flanges: Used to block off the ends of pipelines.
• Reducing Flanges: Allow connection between different pipe sizes without reducers.
• Integral Flanges: These are cast or forged as part of the piping or equipment itself.

Each flange type has specific applications, making it vital to know where and when to use them.

How Are Gaskets Categorised?

Gaskets, essential for sealing flanges, are classified based on their construction:

• Full Face Gaskets
• Ring-Type Gaskets
• Spiral Wound Gaskets
• Metal Jacketed Gaskets
• Inside Bolt Circle Gaskets

For high-temperature and high-pressure applications, spiral wound gaskets are often recommended. They are constructed with a mix of metals for durability.

What Influences Gasket Material Selection?

Selecting the right gasket depends on:

• Material Compatibility: Withstands corrosive properties of the flowing fluid.
• Temperature and Pressure: Perform well under the expected conditions.
• Fluid Type: Gas, liquid, or slurry requires different materials.
• Winding Material: Affects the gasket’s flexibility and sealing capability.
• Cost: Options should balance quality and affordability.

Graphite is a common filler material for spiral wound gaskets used in high-temperature services.

What’s Jacket Piping and Why Is It Used?

Jacket piping involves placing one pipe around another to improve thermal efficiency. The outer pipe circulates heating or cooling fluids like steam or water. It’s typically used for molten substances like sulphur or polymers to prevent solidification.

Does molten sulphur flow easily? Hardly. Jacket piping ensures a steady temperature, so materials like sulphur remain in liquid form. This method is far more effective than steam tracing.

Long vs Short Radius Elbows: What’s the Difference?

• Long Radius Elbows: Cause lower pressure drops and are used in critical systems.
• Short Radius Elbows: Result in higher pressure drops, better suited for confined spaces.

Choosing between these depends on system pressure and available space.

What’s Indian Boiler Regulation (IBR) Piping?

IBR applies to steam lines meeting specific criteria:

• Pressure: Greater than 3.5 kg/cm².
• Diameter: Typically over 10 inches.
• Connection to Boilers: Boiler feed water and condensate lines fall under IBR.

These standards ensure safety under high-pressure, high-temperature conditions.

High Points and Low Points in Piping

• High Points: Air release valves are often placed here to remove trapped air during hydrotesting.
• Low Points: Drain valves are installed to remove leftover water after testing.

Gravity helps water collect at the low points, making drainage more efficient.

Why Is Cryogenic Piping Drained from the Top?

Cryogenic fluids, being extremely cold, often solidify. If drained from the bottom, solids can block the outlet. Top-side drainage prevents such blockages, ensuring smoother operations.

How to Download the Free PDF

Want to have all these questions and answers handy? It’s easy to download the free PDF:

1. Go to Sonu Singh Refinery Website.
2. Navigate to the Blog section.
3. Look for the post titled “Top 25 Interview Questions with Answers”.
4. Scroll down and click the download link.

Share this valuable resource with friends preparing for piping interviews.

Final Thoughts

Piping interviews often test your understanding of practical concepts. By mastering these 20 questions, you’re already ahead of the game. Be confident, revise thoroughly, and stay curious.

Best of luck with your piping interview – you’ve got this!