28 Jawaban Soal Wawancara

ROTATING EQUIPMENT ENGINEER

28 JAWABAN SOAL TES WAWANCARA

by: Eira Patriansyah Arief [email protected] http://rotatingengineer.blogspot.com

28 Jawaban Soal Tes Wawancara by eira© 2

Pengantar Assalamu’alaikum wr. Wb. e-book 28 Jawaban Tes Wawancara ini dimaksudkan untuk membantu para peserta tes seleksi Rotating Equipment Engineer. Namun, e-book ini dapat juga bermanfaat bagi para mahasiswa Teknik Mesin tingkat akhir yang ingin mempersiapkan dirinya sejak dini untuk memasuki dunia kerja berprofesi sebagai Rotating Equipment Engineer. Pihak-pihak selain daripada dua golongan di atas dapat pula menggunakannya untuk menambah ilmunya atau memanfaatkannya untuk menyelesaikan suatu tugas. Soal-soal ini benar-benar diambil dari soal tes masuk sebagai Rotating Equipment Engineer yang sebenarnya pada suatu perusahaan migas di Timur Tengah. Penulis berusaha membuat jawabannya dari berbagai literatur. Soal dan (sebagian) jawabannya sengaja penulis tulis dalam bahasa Inggris dikarenakan bahasa Inggris merupakan kemampuan yang sangat mendasar yang harus dimiliki oleh seorang Rotating Equipment Engineer. Juga wawancara tes seleksi Rotating Equipment Engineer hampir 100% dilakukan dalam bahasa Inggris. Penulis harapkan e-book ini dapat membantu dalam menghadapi tes wawancara dan memberikan sekilas gambaran mengenai ketrampilan dasar yang harus dimiliki oleh seorang Rotating Equipment. Tidak ada gading yang tidak retak, penulis mohon maaf jika ada kekurangan dalam penulisan dan penulis dengan senang hati menerima kritik dan saran. Korespondensi dapat dikirimkan ke: [email protected] .

Depok

Dzulqaidah 1428 H November 2007


1. State any 3 reasons for not pumping of plunger(reciprocating)pump Excessive suction lift, not enough suction pressure above vapor pressure, air in liquid, Suction strainer/filter blocked, no liquid supply, broken valve spring, valves stuck open, bypass valve leaking, worn valves, leaking, pump not rotate due to broken coupling or belt.

2. Draw simple sketch of back to back arrangement of angular contact ball bearing

note that wide lip of outer rings are mated


3. State 5 reasons for mechanical seal failure 1. mishandling (dirty,chipped, scratched, nicked, or other

damages during assembly) 2. Incorrect seal assembly 3. Incorrect seal selection/wrong application. 4. Improper startup. 5. Inadequate instrumentation, tubing, and control system. 6. Fluid contamination. 7. Poor equipment condition. Excessive shaft runout,

deflection, vibration. 8. Wornout seal. Completed lifetime.

4. Name some of the seal flushing plans in API and draw a line diagram of any two of those a. Integral (internal) recirculation from pump discharge to

seal. Plan 1


b. Recirculation from pump case through cyclone separator delivering clean fluid through cooler to seal and fluid trough cooler to seal and fluid with solids back to pump suction. Plan 31

c. Plan 32, injection to seal from external source of clean

fluid. d. Plan 2, Dead-ended seal chamber with no circulation of

flushed fluid. e. Plan 11, recirculation from pump discharge through a flow

control orifice, when necessary, to the seal. The flow enters the seal chamber adjacent to the mechanical seal faces, flushes the faces and flows across the seal back into the pump.

f. Plan 21, Recirculation from pump discharge through a flow control orifice, when necessary, and a cooler and into the seal chamber.

g. Plan 41, recirculation from pump discharge through an orifice, when necessary, to a cyclone separator delivering the clean fluid to the seal chamber. The solids are delivered to the pump suction line.

5. What is the purpose of pumping ring?

Provide an easily and economically renewable leakage joint between pump impeller and pump casing.


6. What is vibration? State unit of measurement of the same Vibration is periodic back-and-forth motion of the particles of an elastic body or medium. It is usually a result of the displacement of a body from an equilibrium condition, followed by the body's response to the forces that tend to restore equilibrium. Free vibrations occur when a system is disturbed but immediately allowed to move without restraint, as when a weight suspended by a spring is pulled down and then released. Forced vibrations occur when a system is continuously driven by an external source. Displacement [mils peak to peak] Velocity [inch per second rms/peak] Acceleration [g peak]

7. How do you identify a leak in a dry gas seal and state 3 reasons for dry gas seal failure Normally only 0.3 – 3 ft3/min. Above that means leaking. Worn face, worn labyrinth, weak spring.

8. Mention any 3 property of a lubricant

Viscosity, pour point, flash point, color, specific gravity, viscosity index.

9. What is oil wedge?

Hydrodynamic force created by lube oil due to shaft rotates that supports the shaft and relocates it within journal bearing clearances. Hydrodynamic principles, which are active as the shaft rotates, create an oil wedge that supports the shaft and relocates it within the bearing clearances. In a horizontally split bearing the oil wedge will lift and support the shaft, relocating the centerline slightly up and to one side into a normal attitude position in a lower quadrant of the bearing. The normal attitude angle will depend upon the shaft rotation direction with a clockwise rotation having an

Lattitude angle

Oil Wedge

Bearing CL

Journal CL


attitude angle in the lower left quadrant. External influences, such as hydraulic volute pressures in pumps or generator electrical load can produce additional relocating forces on the shaft attitude angle and centerline position.

10. Draw general appearance of performance curve of a centrifugal compressor.

11. Draw general appearance of performance curve of a centrifugal pump.

Perhatikan bahwa flowrate semakin tinggi maka head pompa (TDH) akan turun/semakin rendah. NPSHR akan semakin tinggi seiring dengan meningkatnya flowrate pompa. Efisiensi pompa tidak terus menerus naik dengan meningkatnya flowrate, akan tetapi memiliki suatu nilai optimum, Best Efficiency Point (BEP). Berikut ini adalah typical kurva centrifugal pump ISO style dan US style.

Isentropic head

flowrate

efficiency Surge line

Speed 1

Speed 2

Speed 3

flowrate

Efficiency TDH

BHP

GPM

NPSHR


12. What is static and dynamic unbalance? Static unbalance = one plane unbalance. Exist when two unbalance weights line up with each other (in-phase unbalance weights).

Dynamic unbalance = the unbalance weights are neither 0o apart as with static unbalance, nor are they 180o apart as with couple unbalance. This unbalance type is the most common unbalance found in the field. This is combination of static and couple (180o apart unbalance weights) unbalance.


13. What are the safety precautions to be take before beginning job in a hydrocarbon facility? Know what to do and how to do that, Task risk assessment and work permit approval

14. Explain surge and stall!

Surge = condition of fluid flow thru airfoil that become turbulence due to excessive angle of attack. Stall = unstable condition due to excessive surge.

15. How to check labyrinth clearance for a barrel compressor?

Inboard and outboard bearing lift up measurement (diametral clearance), and end play check (axial clearance).

16. How do you centre a centrifugal compressor rotor?

During rotor assembly there is a process “jacking/tensioning rotor studshaft”. Then during installation there is a checking of bearing clearance (axial[endplay] and radial[lift up]) between aft and forward bearing.

17. What is polytrophic head?

The Polytropic Head is an expression used for dynamic compressors to denote the foot-pounds of work required per pound of gas. A Polytropic Process is defined in Thermodynamics as an internally reversible process, which conforms to the relation PVn = Constant.

18. How to check over speed trip (OST) in a small steam turbine?

Manipulate the governor, moving the stem/lever in and out manually several turns on the hand wheel.

19. How to set nozzle clearance in a steam turbine?

Clean casing and nozzle ring sealing surface. Apply a thin coat of paste type sealer and plastic string compound to the nozzle ring sealing surface on the steam end turbine casing. Apply anti-galling compound to the threads of the nozzle ring bolts. Bolt the nozzle ring to the turbine casing. Be sure that lockwashers are used with all bolts. Place lockwashers on the reversing blade assembly bolts and apply anti-galling compound to the bolts threads. Put the bolts through the holes in the reversing blade assembly and slip the spacers over the bolts. Position the reversing blade assy in the turbine casing and bolt it to the nozzle ring. Return the rotor assy to the turbine casing.


20. What is TTV?State its function

Trip and Throttle Valve. To control steam turbine speed by controlling the amount of steam go into steam turbine. It is a safety devices.

21. What is a governor? and State some types of governor

Equipment to maintain engine speed. Isoc = maintain engine at constant speed but variable load. and droop = constant load, variable speed.

22. Name some of the international standard of steam turbine.

a. API 611- General Purpose Steam Turbines. b. API 612- Special Purpose Steam Turbines. c. ASTM D 4248-Standard Practice for Design of Steam Turbine

Generator Oil Systems.

23. What is bump clearance at reciprocating compressor? How to measure and set? Bump clearance = distance between piston head and inner wall of cylinder head Measured by open valve housing, put tin wire, rotate crankshaft until piston move to TDC or BDC. Rotetae backward the crankshaft so we can pull out the tin wire. Measure the thickness of thin wire (thickness = bump clearance). Set it by rotate the locknut at piston rod and crosshead.

24. How to check rod deflection in reciprocating compressor?

Position two dial indicators stem against piston rod close to packing case. Set indicator to zero with the piston toward crankend. Reading are to be taken in vertical and horizontal direction. Bar crankshaft. Measure the reading of dial indicator while piston at mid stroke and at the head end.

25. What is tip clearance Aerial fan cooler and how to measure?

Distance between tip end of fan cooler blade and it circular guard/cover. Using “T” dial gage. Or, if the blade is big enough so curvature error can be neglected, we can use filler gage.

26. Generally what shall be the fit

a) Between inner race of antifriction bearing and pump shaft? Interference fit


b) Between outer race of the bearing and housing? Press fit c) Between coupling and shaft of a centrifugal pump? Wringing

fit

27. Write sequential activities-step involve in bearing replacement on a simple back pull out pump Remove coupling spacer and coupling nut. Tap pump half coupling off its tapered seat. Unbolt bearing housing. Remove cap screws between bearing housing and end cap and loosen socket head screws in deflectors.Slide deflector and end cap against sleeve nut. Lift oil ring over oil ring collar to clear housing. Slide bearing housing off bearings. Remove in sequence: oil ring, bearing lock nut, bearing lockwasher, oil ring collar, ball bearing, oil ring, oil ring collar. Slide end cap and deflector from shaft. Installation: slide deflectors on shaft against sleeve locknut. Slide end cap over shaft against deflectors. Install oil ring collars (for thrust bearing), oil ring, oil ring collar, bearing lock washer, bearing lock nut, and oil ring. Place gasket over inboard end cap and push bearing housing over bearing (be careful with oil rings). Insert dowel and bolt into place. Bring inboard end cap forward and tighten cap srews. Without placing gasket, slide outboard housing over bearing, bring endcap forward and tighten cap screws between endcap and housing finger tight. Measure gap between housing and endcap and remove bearing housing from bearing. Insert gasket with thickness of 0.003” greater than measured gap. Push bearing housing over bearings, insert dowels and bolt into place. Bring outboard end cap forward and tighten cap screws. Check shaft assy for endplay. Should be 0.002”. Slide deflector into place and lock to shaft with socket head set screws. Rotate shaft to check that it is free to rotate and does not bind.

28. In at 3rd stage reciprocating compressor, 2nd stage pressure is

high, what could be problem and how you will rectify? It is caused by flow from 2nd stage to 3rd stage blocked, then pressure build up at 2nd stage. And it can be due to eithers: 3rd stg suction valve blocked/stuck, or 3rd stg piston ring broken, or 2nd stg discharge valve blocked/stuck, or intercooler between 2nd stg and 3rd stg blocked. It can be verified by measuring 3rd stge suction and discharge pressure and temperature, and


compressor overall gas flow rate (check if there is any gas flow reduction).

28 Jawaban Soal Wawancara

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