CHECKS AND PRECAUTIONS FOR SLOW STEAMING

An increasing number of companies are trying the option of slow steaming to save fuel costs at available opportunities. some times due to unavailability of charter or due to instruction of charter ships are forced to sail on slow steaming. Normally when trying out main engine for low load operation we generally try to run the main engine at slowest RPM at which the exhaust boiler can cope and the auxiliary blowers are off and there is no chance that a sudden load change due to course alteration or change in weather will lower the load and allow the auxiliary blower  to cut in intermittently.
Following are the checks and precautions that need to be taken for preparing marine engines for slow steaming of ships:-
CHECKS FOR SLOW STEAMING:- In general in traditional marine engines few checks are needed to be made if low load operation are carried out--

1. Frequent scavenge inspection and under piston area inspection, preferably at the end of the voyage.
2. Check piston rings for breakage, fouling and lack  of springiness.
3. Frequent inspection and cleaning of exhaust boiler.
4. Check cylinder lubrication rate and inspect liners and piston for over and under lubrication and scuffing.
5. Check turbocharger RPM as well as scavenge air pressure.
6. Check and record the temperature difference of the exhaust gas between the inlet and outlet of the turbocharger.
7. Check draft loss of the exhaust boiler if there is an increase by 1.5 times as compared to the non fouled condition at the same load and decrease in steam pressure this may indicate fouling of the exhaust boiler.
8. take frequent indicator cards and check main engine performance.
9. Drain air cooler of water frequently at least twice a watch.
10. Ensure EGB outlet is higher than 165 degree when 20 degree or above is used as pinch point.

PRECAUTIONS AND MAINTENANCE FOR SLOW STEAMING OF SHIPS:- It is well known fact that most breakdowns related to slow steaming occur not during slow steaming itself but when the engine is again operated in the normal range. To avoid any breakdown when the engine is again put back to normal operating mode, certain precautions and routines have to be carried out diligently during slow steaming--

1. Keep jacket cooling water at optimum temperature of about 80- 85 deg and avoid fluctuations.
2. Following periods of slow steaming it is essential that soot blowing operation is carried out prior to increasing of power or shutting down the engine.
3. In load dependent cylinder lubricators slow steaming may lead to lower feed rates hence more suitable higher BN base number cylinder oil may protect against corrosion problems.
4. Reduction of engine load from 90% to 30% increase the resident time inside the cylinder for each charge of cylinder oil by three times. This means higher BN cylinder oil must be used.
5. When lower BN oil is used a higher feed rate must be used as per makers calculation.
6. In case ultra slow steaming is done with auxiliary blowers running then extra electric motors must be supplied and kept on board.
7. Fresh water generation will fall due to reduced heat load hence preheating the jacket water may be considered to generate sufficient water.
8. Exhaust gas temperature after EGB should not be allowed to fall below 165 deg to keep it above the dew point of sulfuric acid.
9. Regular engine load up should be done at least once every day for a period of one hour to around 80 to 85 % of MCR to prevent fouling of the exhaust boiler and the exhaust manifold. 
10. Dry washing of turbine wheel and washing of the compressor must be carried out during the load up.
11. Soot blowing of the EGB must also be carried out additionally during this period.
12. Avoid water condensation in the air coolers and keep scavenge temp around 40 to 45 deg
13. maintain hot well temperature by cooling water control of the condenser and directly allowing some condensate to the hot well by by pass valve.
14. Good maintenance must be done for the fuel injectors.
15. Cold corrosion should be avoided. Care should be taken that cylinder outlet temp should not drop below 250 deg.
16. Fuel oil viscosity should be between 12 to 13 CST
17. maintain high LT temp in central cooling plants for optimum scavenge temp and jacket cooling water temp.
18. FWG may need to be bypassed to maintain jacket temperature on some ships.
19. Keep auxiliary blower continuously on in manual mode to avoid elevated exhaust temperatures after the cut off and before the cut in period. Exhaust temperature above 450 deg can cause hot corrosion and burning of exhaust valves.
20. Low load operation can cause unburnt  fuel and cylinder oil to be accumulated in the exhaust manifold and may suddenly burn causing subsequent over speeding and damage of the turbocharger when load is increased again. Carry out frequent exhaust manifold inspection.