Typical cases
Recently, Chongqing Banan Maritime Affairs Department received a report that a ship in its jurisdiction had insufficient power on its left main engine while going upstream in the Chicken Wing waters, and applied for maintenance outside the Huangxikou waterway.
After receiving the report, law enforcement officers rushed to the scene to check the situation and jointly investigated with the ship. After the engine room was disassembled and inspected, it was confirmed that the elastic coupling of the high-pressure oil pump of the ship's left main engine was damaged and the fastening locking bolt was broken, causing the power transmission between the main engine gear transmission mechanism and the high-pressure oil pump camshaft to be interrupted.
Cause analysis
At this stage, the main marine diesel engines on the Yangtze River Main Line generally adopt the structural model of gear transmission + coupling and the transmission shaft drives the high-pressure oil pump: the crankshaft of the diesel engine outputs power through the gearbox, and drives the camshaft of the high-pressure oil pump through the transmission shaft and coupling to ensure that the diesel engine continues to perform work. This time the coupling gasket and locking bolt were damaged, which directly caused the high-pressure oil pump to stop spinning and fuel injection to terminate, eventually causing the main engine to stall and lose power.
Host drive shaft and coupling position
Damaged coupling gasket
Broken bolt
The stress characteristics of the equipment structure lead to high vulnerability to damage
High-pressure oil pump couplings and locking bolts are the core weak components of power transmission and bear the high-frequency vibration and alternating torsional shear force of diesel engines for a long time. Every time the ship starts and stops, adds or reduces load, or speeds up on the beach, there will be an instantaneous impact load on the coupling gasket and fixing bolts. After long-term reciprocating stress, metal parts are prone to hidden fatigue cracks and material embrittlement, which can lead to coupling displacement, deformation, cracking, bolt breakage and other failures.
Once a component is damaged, it will directly cause two major operational problems: First, the fuel injection timing is misaligned, the fuel injection sequence is disordered, and the cylinder combustion is insufficient; second, the power output is attenuated, the diesel engine has insufficient explosion pressure, power drops, and abnormal smoke exhaust. In severe cases, it will directly lead to the main engine stalling.
High temperatures and harsh working conditions during flood season accelerate component failure
In the high-temperature environment during the flood season, the cabin is sealed and stuffy, and heat dissipation is poor. The overall operating temperature of the equipment increases significantly, the toughness of metal parts decreases, and the aging rate accelerates. At the same time, the water flow is turbulent during the flood season, and the ship needs to operate at full load for a long time when going up to the beach. The main engine torque output is large, and the load peak of the transmission system is high, which greatly exceeds the normal navigation conditions, accelerating fatigue tearing of the coupling gasket and shearing fracture of the locking bolt.
There are obvious shortcomings in daily operation and maintenance inspections
Inadequate prediction of hidden dangers. The crew's daily inspections focused on obvious faults such as abnormal noise and oil leakage of the main engine, but ignored the loss of hidden small parts such as couplings and fixing bolts, and failed to discover hidden cracks, looseness, and fatigue aging problems of components in a timely manner.
Lack of research and judgment on abnormal working conditions. On the premise that there is no significant change in the ship's load, the company fails to actively pay attention to subtle changes in exhaust temperature and exhaust smoke color, misses the early warning of failure, and turns small hidden dangers into sudden dangers.
Maintenance and assembly are not standardized. The high-pressure oil pump coupling is a precision transmission structure. Some ship maintenance does not strictly follow the manufacturer's manual. There are problems such as coaxiality deviation, substandard tightening torque, and inaccurate timing calibration. Assembly deviations lead to increased vibration and uneven stress during equipment operation, which greatly shortens the service life of the equipment.
There are loopholes in the management of shipping companies
The company's maintenance system is extensive, and hidden wearing parts such as oil pump couplings are not included in the maintenance list, and there is a lack of regular preventive replacement mechanisms.
The training is not targeted enough, and there is a lack of training on identifying hidden dangers of equipment in working conditions. It is difficult for crew members to detect the precursors of failure such as smoke exhaust and abnormal temperature.
There is a lack of shore-based supervision, and the behavior of ships beaching at full capacity for a long time is not controlled during the flood season. The safety risk assessment of voyages is superficial.
Rectification and disposal situation
Enforcement officers required the vessel's crew to dismantle the high-pressure fuel pump drive assembly, remove and replace fragments of broken bolts and damaged gaskets, and thoroughly inspect the drive shaft, gearbox interface and fuel pump camshaft to confirm the absence of secondary wear, deformation or damage. Fuel-injection timing, component coaxiality and bolt-tightening torques were then checked precisely to ensure accurate drive alignment, even loading and correct timing. After assembly, staged no-load, half-load and full-load test runs were carried out, with the drive components monitored by sound and the exhaust smoke and temperature observed. Once the main engine's power had returned to normal and stable equipment operation without abnormalities was confirmed, a tug assisted the vessel throughout the journey to its destination port.
Relevant situations and existing problems are notified to the shipping companies and management departments to which the ships belong, and companies are clearly required to consolidate their main responsibilities, carry out comprehensive self-examination and self-correction of similar electromechanical equipment based on problems, improve daily inspections, maintenance, and personnel operation control mechanisms for ship equipment, draw inferences from one instance to investigate and rectify similar hidden dangers, and strictly prevent similar equipment failures and safety issues from recurring.
Based on the analysis of this typical fault case, in view of the high temperature, high load, and complex navigation conditions of the Yangtze River during the flood season, the shipping companies and crew members in the jurisdiction are reminded as follows:
Establish a targeted special inspection mechanism
Turbine managers must pay close attention to hidden wearing parts such as high-pressure oil pump couplings and transmission bolts, and turn fault repairs into proactive prevention. Carry out special inspections on a regular basis, focusing on checking the operating status of the high-pressure oil pump transmission shaft, so as to ensure early detection and early disposal of hidden dangers.
Pay close attention to signs of abnormal host operation
Pay attention to the operating parameters of the main engine during the entire voyage. When the ship load is stable and unchanged, if there are black exhaust smoke, abnormal increase in exhaust temperature, sudden high and low power, abnormal vibration in the engine room, etc., priority will be given to determining the transmission failure of the high-pressure oil pump coupling, and the ship will be anchored in the nearest safe water area for investigation as soon as possible. It is strictly prohibited to sail while sick or forcibly beach the ship.
Strictly standardize maintenance and assembly standards
The high-pressure oil pump coupling and transmission system are precision matching structures and are strictly prohibited to be disassembled and assembled blindly based on experience. All disassembly, replacement, and assembly operations must strictly follow the manufacturer's maintenance manual and strictly control the three core parameters of injection timing, coaxiality, and tightening torque to prevent secondary failures caused by assembly deviations.
Strengthen management and control of high-temperature equipment during flood season
During the high-temperature flood season, the frequency of inspections of electromechanical equipment should be increased, the engine room cooling equipment should be cleaned in a timely manner, and the engine room ventilation and heat dissipation conditions should be improved; the main engine should be prevented from beaching operations at full load for a long time, and the navigation load should be reasonably regulated to reduce the instantaneous impact load on transmission components and delay equipment aging and loss.
Company safety management suggestions
All shipping companies need to improve the ship's electromechanical equipment maintenance system, establish maintenance plans for key equipment, conduct regular inspections and maintenance, strictly implement inspection points and maintenance standards, and eliminate problems such as inspections going through the motions, missed inspections of key parts, and missed identification of hidden dangers. It is strictly forbidden to serve beyond the specified period and operate while sick. On the other hand, shipping companies should further strengthen crew safety education and training and voyage safety risk assessment during high-temperature flood seasons, and prevent accidents caused by mechanical and electrical failures from the source of equipment management.
Source: Changjiang Maritime Release
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