Thursday, February 24, 2011

ME CRANKCASE OIL MIST DETECTOR ALARM , ON CHEMICAL TANKERS-- CAPT AJIT VADAKAYIL


Yesterday I was in Chennai MMD to get my Masters' Certificate of competency revalidated.

A  junior engineer appearing for his exams, recognised me from my blog photograph , and thanked me for writing valuable engineering stuff.  The same happened 3 weeks ago with a 2nd engineer.

To both I had this to say " My engineering posts are NOT for passing exams, but for you to work safely and bring your hard earned money home. Because hardly anybody else cares for your safety. This is why enclosed lifeboats have been falling for 30 years , thousands of AE conrods have been busting -- and 500 MIG 21 fighter jets have crashed, with no early solution in sight".

(Read my post dated Nov 22nd -- THE FLYING COFFIN MIG 21--  FISH BEDS OF IAF )

This motivates me to post another one.

I do NOT care for vested patronising praises from shore chairs. A genuine compliment received from a sailing engineer is indeed taken and valued.

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                                         OIL MIST DETECTOR ALARM – Capt Vadakayil

Ck
Sr No

Description

1
You must be familiar with the oil mist detector fitted on YOUR ship. Read the manual and check the number of detection points in the crank case.

2
Temperature sensors monitors only main bearings, --- if you ME is fitted with oil mist detector it monitors ALL bearings as well as the piston rod hotspots .

3
Be aware that modern oil mist detectors using light scatter as sensing method rarely give false alarms unlike old oil mist detectors using the principle of obscuration where lenses become fogged.  It is better to assume that the LEL of 50 mg MECC oil/ litre has been exceeded which can ignite at temperature of about 200 deg C

4
A fine mist of MECC oil of size 3 – 10 mic will catch fire faster than a mist of gasoline/ Naphtha

5
Quickly thermocheck Crankcase doors using finger tips to detect any temp deviations of  units.

6
Check bearing temperatures if crankshaft bearing  monitoring system is dually provided.

7
White metal inside CC indicates bearing failure and MUST be reported by ER crew to C/Eng.

    ACTION
Ck
Sr No

Description

1
Inform bridge and find out traffic condition or possibility of running aground..

2
Inform Chief engineer

3
Change over controls to ECR & reduce engine speed at once and prepare for stoppage. Reduction of rpm will minimize further creation of oil mist. However the ships forward momentum will cause propeller will turn the crank shaft.

4
Increase the cooling of bearings by increasing MECC oil circulation.

5
If the problem is due to blow past , cut out Fuel pump on ME unit affected if stopping has to be delayed.

6
Stop ME . Engage the turning gear. Keep FFA  in readiness.

7
Open sky light, ventilate engine room and crew away from ME crankcase doors and more important , crankcase relief valves / flame arrestor.

8
Continue with lubrication for at least 30 minutes.  Do not open crankcase doors for at least 30 minutes after stopping, to avoid closing the fire triangle with oxygen.


9
Stop the lub oil pump.  Open all lower most doors , and try to locate hot spot.  Look for discoloration at the surface, squeezed out white babitt metal. Find out the hot spot by looking for excessive flow of lub oil, high temperature at sliding surfaces .

10
After repairing defect, start Lub Oil Pump and check oil flow through each bearing, while turning the engine on turning gear.

12
Clean the detector and check the `ZERO’ setting and sensitivity test of the mist detector.

13
Start the engine and gradually increase the speed.

14
Stop the engine again after about 15 minutes of running and do a MOST serious recheck.





Notes:--
When a Crank Case explosion occurs usually there is another secondary explosion due to sudden inrush of fresh air into the vaccumised crank case.

Oil mist builds up when the equilibrium is lost—generation of oil mist versus condensation on colder surfaces and drainage back into crankcase and sump.

Modern oil mist detectors also measures crank case pressure in the event of large pressure buildup by piston seal leakage, giving an alarm and an auto shutdown. The detection points are sensed simultanelously , not one by one using microprocessors.

CC explosions and pressure piling usually cause loss of life. ER fires are caused by mist being sucked towards air inlet of turbocharger.

Bearings become hot usually due to insufficient TOP clearance restricting flow of MECC leading to hot spots.

Spurious piston rod stuffing box parts like springs have also caused CC explosions.

Flame arrester quenches the slower propagating flame front preventing a major ER fire.


CAPT AJIT VADAKAYIL
..

2 comments:

  1. Oil Mist detector [or the alarm] failure is an expensive affair bcoz when such failure happens, UMS notation is suspened and ship's compliment should be increased [immediately fly additional crew] to increase the manning to a non-UMS level. As a surveyor I have seen this couple of times.

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  2. The oil mist alarm detector is very helpful thank for this blogs.
    Long range Metal Detectors | Detech metal Detectors

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