I. Overview of Fault Phenomena
The vessel is an old ship of a certain company with an age of over twenty years. The main propulsion diesel engine (referred to as the main engine) of this ship is of the SULZER type. It is a crosshead long-stroke low-speed two-stroke diesel engine. Both the cylinder liner and the piston are cooled with fresh water, and the piston is cooled by water supply through a water supply pipe.
The turbocharger adopts an independent lubricating oil system, and the main lubricating oil is cooled by seawater.
The laboratory analysis report sent back by the ship indicated that the water content of the main engine lubricating oil was too high. On the one hand, the ship took measures, started the lubricating oil separator to separate the main engine lubricating oil, and at the same time replenished some new oil.
In addition, to verify the composition of the lubricating oil, samples were taken again at the next port for inspection. It was particularly noted that the moisture content in the lubricating oil needed to be tested. The inspection report once again confirmed that the moisture content in the lubricating oil was too high and showed an upward trend, approaching the limit of the usage standard.
Due to the fact that lubricating oil has functions such as lubrication, cooling, rust prevention, cleaning, sealing and buffering, its quality is the key to ensuring the normal operation of diesel engines. If the water content increases, it will destroy its lubricating performance, corrode the metal surface, accelerate the wear of components, and even cause emulsification, losing the function of lubricating oil. The problem is very serious.
II. Composition of the lubricating oil System of the main engine
The crankcase oil system of this main engine adopts a dry oil pan type lubricating oil system. That is, the lubricating oil circulation cabinet is set under the oil pan of the diesel engine. The lubricating oil pump sucks oil, and after being cooled by the lubricating oil cooler, it is sent to each lubrication component. After lubrication, it flows back to the bottom of the diesel engine by gravity and finally returns to the lubricating oil circulation cabinet.
The lubricating oil circulation cabinet is located in a double-layer bottom, and there are dry compartments all around it.
The lubricating oil separator can purify and circulate the lubricating oil in the lubricating oil circulation cabinet, and also send the purified lubricating oil in the lubricating oil circulation cabinet to the lubricating oil daily cabinet or to the main unit for warm-up. The working pressure of the lubricating oil is 0.3 to 0.4MPa.
The turbocharger adopts an independent lubricating oil system.
III. Analysis of Lubricating Oil Water Ingress Fault
Based on the results of the lubricating oil test analysis, the rate of water increase is very slow, indicating that the leakage is due to seepage and the amount is not large. According to the composition of the diesel engine's lubricating oil system, we have analyzed the possible causes of the leakage as follows:
(1) The cooling tube bundle of the lubricating oil cooler cracked and leaked, allowing cooling seawater to flow in.
(2) The joint of the piston water pull tube is damaged, allowing water to flow into the piston.
(3) Cracks in the cylinder liner or cylinder head cause water leakage, or water leakage from the cooler of the purge box seeps into the crank box through the piston rod stuffing box.
(4) There are cracks in the circulating oil tank, and water is leaking into the surrounding compartments.
(5) There is leakage in the flange or gasket of the bilge lubricating oil system pipeline, and the bilge sewage leaks in.
(6) Lubricating oil separator;
(7) Water leaks into the crank box through other means;
We follow the basic approach to troubleshooting, analyzing and eliminating problems from the simple to the complex and from the surface to the core.
1. Inspection of the lubricating oil cooler
The lubricating oil cooler of this main engine uses seawater for cooling. The fluid flowing inside the cooler tubes is lubricating oil, while the fluid flowing outside the tubes is seawater. During normal navigation, as the lubricating oil pressure is greater than that on the seawater side, water will not leak into the lubricating oil. When the engine stops working, the lubricating oil pump stops working, and although the seawater pump of the lubricating oil cooler also stops working, However, due to the static pressure of seawater, it is also possible for seawater to leak in through the rotten tube bundles of the cooler.
Remove the end cover of the cooler, start the lubricating oil pump of the main unit, adjust the oil pressure to the normal operating pressure, and check if there is any lubricating oil flowing out of the cooler. If there is oil flowing out, it indicates that there is a leakage in the cooler tube bundle.
2. Inspection of the piston water pull tube
The piston of this main unit adopts a tube-in-tube water cooling mechanism. Start the piston water pump, adjust it to the water pressure during the operation of the main unit, connect it to the turning machine for turning, and inspect the connection parts and water pulling tubes of each cylinder one by one. No leakage was found in the water pulling tubes, and there was no water accumulation at each connection interface.
3. Inspection of the piston rod stuffing box
The piston rod stuffing box is a sealing device installed in the center hole of the cylinder block bottom plate (or transverse partition plate), which has the functions of sealing the sweeping air of the cylinder, scraping off the oil stains on the piston rod and separating the cylinder from the crankcase.
If the cylinder liner, cylinder head or purge box of the cylinder leaks and the packing box seal is not good, it may cause water to leak into the crank box.
We inspected the piston rod stuffing box, checking its surrounding conditions and sealing conditions. We found that there was not much dirt around and no large amount of water. The sealing of the stuffing box was good, and the possibility of water leakage from here to the crank box was ruled out.
4. Inspection of the circulating oil tank
There are dry compartments around the circulating oil tank. When the doors of the dry compartments around were opened, no water was found in the compartments. After checking the area around the circulating oil tank, no water was found leaking directly into it. At the same time, we also carefully inspected the measuring tubes of the circulating oil tank and found no damaged areas. This indicates that water leakage in the circulating oil tank can be ruled out.
5. Inspection of the bilge circulation oil pipe system
Start the lubricating oil pump of the main engine and inspect the lubricating oil piping system, flange connections and gaskets arranged at the bottom of the cabin. No oil leakage was found, indicating that even if the water at the bottom of the cabin usually flooded the lubricating oil piping system, water could not leak into the circulating oil system. Moreover, the amount of lubricating oil does not change much in normal times, so the piping system should be normal.
6. Inspection of the lubricating oil separator
First, check the steam heater of the lubricating oil separator and start the lubricating oil separator.
Disassemble the end cover of the steam heater and check if there is any oil leakage from the steam heating tube bundle. If there is oil leakage, it indicates that there is a leak in the steam heating tube bundle. If no oil leakage is found, it means that the steam heater is working properly.
Secondly, check whether the lubricating oil separator is working and whether there is any water flowing into the oil.
According to its operation status, the water in the elevated water tank of the lubricating oil separator did not significantly decrease during operation. We also conducted tests on the oil purified by the separator, and the water content was almost zero, indicating that no water leaked into the lubricating oil during the operation of the separator.
Finally, the piping systems and valves of the oil separator to the main unit's circulating oil cabinet were inspected, and no abnormalities were found.
7. Water leaked into the crank box through other means
After the above inspection, no water was found to have leaked into the lubricating oil system of the main unit. It seems that the water has leaked into the lubricating oil through other means.
Some water was found around the cylinder head of the main engine. This water seeped out from the connection between the cylinder liner and the cylinder head. Due to the cold weather at that time, many gaskets had aged, causing the water to leak and accumulate around the cylinder head.
After carefully analyzing the structure of the main engine, it seems possible that this water will seep into the lubricating oil of the crankcase. It will seep in slowly through the through bolts. In the crosshead diesel engine, the function of the through bolts is to connect the cylinder block, frame and base into one, forming the fixing part of the diesel engine.
There was water around the through bolts beside the cylinder head. From this, we wondered if the water might seep into the lubricating oil of the crankcase main engine through the through bolts. Due to the tight navigation mission, there was no time to lift the cylinder to eliminate the leakage at that time, so we could only take temporary measures. Therefore, we first dried the areas with water around the cylinder head and surrounded the through bolts with sealing mud to separate the water from the through bolts.
Start the main engine lubricating oil separator to purify the lubricating oil in the main engine circulation oil tank. After the voyage ends and the vessel docks, send the lubricating oil sample for inspection. The inspection results show that the moisture content of the lubricating oil begins to decrease, and water seeps into the crank box through the through bolt.
Subsequently, the main unit carried out a cylinder lifting inspection, replacing all the leaking cylinder head gaskets with new ones. The water content of the main unit's lubricating oil gradually decreased, completely eliminating this fault.
IV. Analysis of the Causes of the Fault
Analysis of the cause for the leakage of this round of water into the lubricating oil of the crank box main unit through the through bolt:
(1) The large tube wheel of this vessel was seriously lacking in responsibility. When there was water leakage and water accumulation around the cylinder liner, the chief engineer repeatedly urged it to lift the cylinder for maintenance. However, the large tube wheel believed that the transportation task was heavy and the time was tight, and would wait until there was spare time to carry out the maintenance, constantly delaying.
It is also believed that this minor leak will not affect the operation of the main unit.
In addition, I was about to take a public break and didn't want to hoist the pole for maintenance, which led to this malfunction.
(2) The crew members did not attach enough importance to it in their minds. As it was an old vessel, the engine room personnel thought that minor leaks were normal and did not pay sufficient attention to it.
(3) The ship is old, and many O rubber rings or gaskets have aged and not been replaced in time. During winter, the engine room insulation is insufficient. Especially when sailing to northern ports, the rubber gaskets and washers harden severely, resulting in water leakage in many places on the cylinder head and water accumulation in the surrounding accessories.
(4) The SMS (Ship Safety Management) system on board was not strictly implemented. No measures were taken for leakage, spillage, dripping and seepage, but rather a laissez-faire attitude was adopted.
V. Summary
The fault of water leaking into the lubricating oil of the main engine crank box through the through bolt is extremely rare, but it still occurred in this wheel.
The lesson we have learned from this malfunction is:
(1) For the management of old ships, the engineer must have a strong sense of responsibility and strictly follow the SMS formulated by the company. Regular maintenance, servicing and inspection should be carried out to prevent potential accidents.
(2) Due to the large amount of work involved in the management, maintenance and upkeep of old ships, we cannot focus on the major issues and neglect the minor ones. We must also take measures to eliminate leakage, spillage, dripping and seepage. We need to eliminate potential accident hazards. If the hoist cylinder of this vessel had been inspected earlier, such faults could have been completely avoided.
(3) Lubricating oil should be sampled and analyzed regularly. If the lubricating oil of this wheel is not tested regularly, the consequences would be unimaginable.
In conclusion, lubricating oil is the lifeblood of a diesel engine's operation. The slightest mistake could lead to a serious accident.
Although the increase in the moisture content of the lubricating oil was discovered in a timely manner in this round and no losses were caused, it is still worthy of deep consideration by the engineer.