Piping Basics of Piping 5 — Questions and Answers
Question 1: What is the primary difference between a weld neck flange and a slip-on flange?
- Weld neck flanges cannot be used above 150# rating
- Weld neck flanges have a long tapered hub and use a full-penetration butt weld; slip-on flanges slide over the pipe and use fillet welds (Correct answer)
- Slip-on flanges are stronger than weld neck flanges
- Weld neck flanges are only used on plastic pipe
Correct answer: Weld neck flanges have a long tapered hub and use a full-penetration butt weld; slip-on flanges slide over the pipe and use fillet welds
Weld neck flanges are stronger and better suited for high-pressure or cyclic service due to their tapered hub and butt weld, while slip-on flanges are easier to align but have lower strength.
Question 2: What is the purpose of a spectacle blind (spade) in a piping system?
- To increase pipe flow capacity
- To provide positive isolation of a line section for maintenance or testing (Correct answer)
- To reduce vibration between flanges
- To connect pipes of different pressure ratings
Correct answer: To provide positive isolation of a line section for maintenance or testing
A spectacle blind is a device inserted between flanges that provides positive, visible isolation of a piping section, ensuring that no fluid can pass during maintenance operations.
Question 3: In a piping isometric drawing, what does a '45° elbow' symbol indicate?
- A change in pipe material
- A pipe bend of 45 degrees changing the flow direction (Correct answer)
- A flanged connection at 45 degrees
- A pipe slope of 45 degrees for drainage
Correct answer: A pipe bend of 45 degrees changing the flow direction
A 45° elbow fitting changes the flow direction by 45 degrees and is shown on isometric drawings with a specific symbol to indicate both the fitting type and the direction change.
Question 4: Which type of gasket is typically used between raised-face flanges in high-pressure service?
- Full-face rubber gasket
- Spiral-wound metallic gasket (Correct answer)
- Compressed fiber sheet gasket
- Cork gasket
Correct answer: Spiral-wound metallic gasket
Spiral-wound gaskets, made of alternating metal and filler material, are preferred for high-pressure raised-face flange connections because they provide excellent sealing under high bolt loads.
Question 5: What is the purpose of pipe insulation in process piping?
- Only to prevent burns from hot surfaces
- To conserve heat or cold, prevent condensation, and protect personnel (Correct answer)
- To increase pipe structural strength
- To prevent water hammer
Correct answer: To conserve heat or cold, prevent condensation, and protect personnel
Pipe insulation serves multiple functions: it reduces heat loss or gain to improve energy efficiency, prevents condensation on cold lines, and protects workers from contact with hot or cold surfaces.
Question 6: What is 'dead leg' in a piping system and why is it a concern?
- A pipe run with no supports, causing sag
- A section of pipe with no flow where fluid stagnates, risking contamination or corrosion (Correct answer)
- A valve locked in the closed position
- An underground section that cannot be inspected
Correct answer: A section of pipe with no flow where fluid stagnates, risking contamination or corrosion
A dead leg is a section of piping where fluid does not flow, creating a zone where bacteria can grow, corrosion can accelerate, or product quality can degrade — a particular concern in pharmaceutical and food processing systems.
Question 7: Which piping symbol on a P&ID represents a gate valve?
- Two triangles pointing toward each other at their tips (Correct answer)
- A circle with an X through it
- Two triangles pointing away from each other
- A filled circle on a line
Correct answer: Two triangles pointing toward each other at their tips
On a P&ID, a gate valve is represented by two triangles with their points meeting at the centerline of the pipe, symbolizing the wedge-shaped gate disc that slides perpendicular to flow.
Piping Basics of Piping 5
What is the primary difference between a weld neck flange and a slip-on flange?