Mechanical Maintenance Common Questions

EPC School 2012

M for Mechanical

Topic - Maintenance

1. What is meant by LLF and why it is being carried out for machine monitoring  ?

2.  What is difference between preventive maintenance and condition based maintenance Programs ?

3. How will you check correct direction of NRV, while installing?

4. What is the function of steam trap?

5. What are the different types of scaffoldings being used?

6. Which piping standards are we following?

7.  What are the various types of piping flanges?

8. How we are specifying a bolt ?

9. What is the significance of schedule in piping specification ?

10. What is difference between butt weld, fillet weld and socket weld ?

11. Where do you find application of globe valves?

12. What are the different types of valves?

13. What is difference between bolt torque tightening and bolt tensioning?

14. Differentiate following fits: Interference fit, transition fit, clearance fit.

15. What is the difference between Flexible coupling and rigid type coupling?

16. Where do you find application of fluid coupling?

17. What are the different types of gears used?

18.What is meant by “Hydrodynamic Lubrication”?

19. When we are using PSV and PRV? State the difference between the two.

20  How will you identify a piping Spacer and a Blind already installed?

21 What is the significance of piping Flange Rating, i.e. Class 300#, Class 600#

22 Why do we use eccentric reducer?

23 State 5 types of piping supports.

24  Why do we need to set spring supports at their Hot & Cold set point?

25 What is “Hot alignment” in a machine? Why do we need to carry out?

Answers to the above questions:

1. LLF is abbreviation for Look, Listen and Feel . LLF is being carried out to asses the machine condition by inspecting for visible abnormalities like leaks and audible changes like abnormal noise.

2. PM is a schedule based frequency based maintenance requiring the equipment to be in stopped condition while CM is condition maintenance carried out

3. The arrow marked on NRV should be oriented pointing along fluid flow.

4. To enable condensate from steam system to drain out while preventing steam from escaping

5. Light, Medium and Heavy duty scaffoldings.

6. ASME B 31.3

7. Socket weld, Weld Neck, Slip-on, Lap Joint, Threaded

8. By Specifying Size, Type of threads, TPI, Material Specifications and Length e.g. ¾” 10 UNC A193 B7 180

9. Schedule indicates thickness of the pipe and hence defines the rating of the pipe.

10. Butt weld is joining two plates in same plane, Fillet joint is overlapping of two plates. Socket weld is insertion of pipe inside the socket & seal welding.

11. For flow controlling

12. Gate, Globe, Ball, Plug, Needle, Butterfly valves

13. In Torque tightening, bolt is tightened to a required torque value using torque wrench, while in bolt tensioning bolt is pre-stretched and then nut is tightened.

14. Interference fit: Bore dia is less than the shaft dia

Transition fit: Bore dia is same as the shaft dia

Clearance fit: Bore dia is more than the shaft dia.

15. Flexible coupling accommodates limited movement of the shafts and compensates by flexing to any misalignment. Rigid coupling does not permit this.

16. For high initial torque & for shock load absorption , e.g. in conveyor belt, Ball Mills etc

17. Spur, Helical, Bevel, Spiral Bevel

18. Oil forms a wedge between journal and bearing faces which gets squeezed and in turn generates a high reactive force that supports the journal

19.  PSV is used to avoid increase in pressure beyond a defined set pressure to protect the system. PRV is used to reduce and maintain /control a pressure at a pre-defined value.

20. A tail blind is provided with one hole on the tail, while a spacer is provided with 2-holes on the tail.

21. Flange rating defines the maximum allowable pressure for a range of various temperatures.

22. To avoid flow separation and air pocket, normally at pump suction.

23. Shoe support, spring support, hanger, clamp type, Guide support

24. Spring supports are to be set at Cold ( White) point when pipeline is not charged with the hot liquid , to compensate for thermal expansion and liquid loading these are to be set at RED mark( Hot Point) after pipeline is charged with the liquid.

25. Alignment which is done at operating temperature of the driver and driven equipment is called Hot alignment. It is required to be done as equipment shaft centerline changes with the operating temperature and will be running in misaligned condition if the alignment is done at ambient temperature and not corrected in hot condition.