INFORMATION SHEET
MAIN ENGINE CASUALTIES
Information Sheet Number 62P-206
INTRODUCTION
Main engine casualties have a serious impact upon a ship's ability to complete its mission because they directly affect mobility by restricting or eliminating use of a shaft. As casualties occur to the main engine, it is essential that prompt action be taken to minimize damage and restore propulsion as soon as possible. A ship without propulsion is a sitting target.
REFERENCES
(a) Engineering Operational Casualty Control manuals
(b) Damage Control, Engineering Casualty Control NSTM Chapter 079 Vol III
INFORMATION
A. MAIN ENGINE CASUALTIES
1. Main engine casualties can be grouped broadly into three categories: those due to lube oil system problems, those due to main condenser problems and those due to a loss of steam pressure. Even though grouped in different categories, the actions required for and affects from each are the same or similar. The purpose of the actions for all casualties is to minimize damage and restore propulsion.
a. Lube oil system casualties are very serious because of the greater probability of extensive damage and expensive repairs. If detected and corrected quickly, damage usually is avoided or minimized. Although main engine bearing inspection or subsequent repair is a moderately expensive and time-consuming process, damage to a main engine turbine or reduction gear is far more costly and complicated to repair. Lube oil system-related casualties include: loss of main engine lube oil pressure, hot or uncontrollable hot bearings (main engine, reduction gear and line shaft), and major lube oil leaks from the main engine. Restoring normal lube oil pressure and flow as soon as possible is paramount. Stopping and locking a shaft precludes use of the shaft and minimizes the extent of damage. The procedures taken for all stop and lock casualties are the same and are covered in detail below. Unless the engine can be restored to safe operation within five minutes after the shaft is stopped and locked, the rest of the engine, including the condenser must be secured. (Although an unusual noise and vibration casualty may or may not be caused by the lube oil system, the procedures for stopping and locking for a metallic noise are identical to the lube oil system casualties that require stopping and locking of the shaft.)
b. The second group of procedures involves breaking main condenser vacuum. If main condenser vacuum cannot be maintained or the shaft is idle and has not been or cannot be rotated within five minutes after stopping and locking, the engine must be secured and vacuum broken to place the engine in a safe condition. These procedures are detailed below.
(1) Main condenser casualties center around problems with vacuum and circulating water systems. Without the main condenser vacuum to condense the steam from the turbines, the engine cannot be used. It is important to note that in this type of casualty, one symptom can affect another, making it difficult to locate and correct the cause. An example is that a malfunction of the thermostatic recirc valve causes the condensate, hotwell and air ejector condenser temperatures to increase. This causes the vacuum to drop in both the air ejector condenser and main condenser. Since the first indication of a problem usually is the drop in main condenser vacuum, investigating for the cause will reveal all these other symptoms which make identifying the actual cause very difficult.
(2) Main condenser casualties are either a loss of main condenser vacuum or a "hot condenser." A "hot condenser" is one in which the temperature of the water in the inlet or outlet header has reached 140 degrees F or the header is hot to the touch.
(3) The first action taken when a loss of main condenser vacuum occurs is to check the inlet and overboard header temperatures of the main condenser to verify that the condenser is not "hot." A hot condenser requires immediate action to prevent serious material problems to the main condenser through overheating and distortion. In an extreme case, the rubber expansion joints can rupture and cause major flooding. If the condenser is not hot, then controlling actions are taken to locate and correct the cause. If vacuum continues to drop, the engine must be slowed in standard speed increments as vacuum drops to specific levels. If the condenser is hot, the engine is secured immediately. If the main circ pump was not running, do not start it. If it was running, stop it, since operating it can rupture the expansion joints from thermal shock.
c. Sometimes a casualty to the boiler has an effect upon the engine only because steam is no longer available to power that engine and its support systems. The engine has sustained no damage. Upon a loss of steam pressure casualty that requires securing the engine, the same procedures outlined above for securing the main engine during a loss of vacuum casualty are followed. In split plant ships, casualty control procedures are designed so that the plant is cross connected and steam supplied to the engine from the other plant. If this is done, the engine will be secured only until steam pressure is restored from the other plant.
In all main engine casualties, the Engineer Officer must determine the extent of damage, required repairs and restoration procedures.
B. STOPPING, LOCKING AND UNLOCKING A MAIN SHAFT.
1. There are times when a main shaft must be stopped quickly and prevented from rotating any further to minimize potential damage. Although a shaft can be locked or unlocked with or without way, it is preferable to unlock the shaft with no way on for safety of personnel and equipment. The following discusses stopping and locking a shaft while making way and unlocking it with no way.
a. The opposite throttle is opened to stop the shaft from rotating and hold it in place. If going ahead, shut the ahead throttle and open the astern throttle, admitting just enough astern steam to stop the shaft. The shaft is held stationary for five to ten seconds so the watch team knows that it has control of the shaft. The jacking gear is then engaged and the brake set to hold the shaft in position and keep it from rotating. All these actions take place under the direction of the MMOW, relying largely on hand signals to direct the throttleman. Once locked, the guarding valve is shut, steam pressure drained from the steam chest and the throttles locked to prevent operation of the engine while the shaft is locked.
b. In split plant ships, the unaffected engine is slowed to "emergency standard" speed if above emergency standard speed. If at or below emergency standard, the unaffected engine stays at the ordered speed. Emergency standard is a prescribed speed at which casualties are handled. It is different for each ship class and is a function of the capabilities of the plant. It is a speed at which a ship is able to respond to emergencies without impact on the unaffected plant.
c. There are speed limitations associated with a locked shaft. This is a function of the ability of the jacking gear and brake to hold the shaft against the force exerted upon it by the propeller being dragged through the water. This speed is different for each ship.
d. When main engine vacuum is broken, the shaft does not have to be stopped and locked, it can be left trailing. The speed limitation on trailing a shaft is a function of the heat generated by windage. This means that there is no steam flowing across the turbines which are spinning in air, building up heat from friction. The steam flow actually cools the turbine blades. Again, this is a specific speed for each ship class.
e. Unlocking the shaft with no way on the ship is the least dangerous of all options. Although the movement of the water past the propeller will not turn the shaft when moving slowly through the water, the ship is brought to a stop and verified to have no way on. The jacking gear is disengaged and the engine tested. Before deciding to disengage the jacking gear, some determination usually has been made that the engine is satisfactory enough to warrant testing it. Before stopping the ship or starting to disengage the jacking gear to unlock the shaft, the engine is prepared for operation by starting the support systems and drawing a vacuum on the engine. This means that the jacking gear is running, turning the shaft to prevent it from bowing, when stopping the ship. The jacking gear must be stopped before disengaging it.
C. SPECIFIC INFORMATION CONCERNING DIFFERENT MAIN ENGINE CASUALTIES.
1. LOSS OF MAIN ENGINE LUBE OIL PRESSURE. One of the most serious main engine casualties, it has the potential to completely destroy the main engine turbines and reduction gears. Indications include the low lube oil pressure alarm sounding, the electric lube oil pump starting for no apparent reason, a drop in lube oil system pressure, no or diminished oil flow in sight flow indicator(s), higher than normal lube oil bearing temperatures. The common causes are failed lube oil service pump, clogged lube oil strainer, lube oil unloading valve malfunction, lube oil piping rupture/major lube oil leak/spray, low main engine lube oil sump level, and clogged return line on a sight flow indicator.
a. This casualty usually requires that the affected engine be stopped and locked, especially if the low lube oil pressure alarm sounds or no flow is seen in the sight flow indicators. The watch team makes every attempt to regain lube oil pressure unless the cause is a rupture or leak.
b. If the cause is a leak or rupture, specific actions are taken to prevent a fire from breaking out, as well as the normal actions to limit the damage to the engine. AFFF bilge sprinkling is activated and firefighting equipment manned. The shaft is stopped and locked so that the lube oil pumps can be stopped since they are pressurizing the lube oil. The spray or leak is deflected away from hot surfaces, if possible, and the fire hazard is flushed to the bilge and removed from the ship.
c. Leaks are caused by failed gaskets, loosened fittings on piping or system components, incorrect maintenance and piping deterioration. More common than all the above causes is operator error. Specifically, improper shifting of the lube oil strainers (allowing the integrity to be broken when pressurized) and losing the seal on the lube oil purifier while it is operating are often the cause of these leaks.
d. If a shaft is stopped and locked, that shaft cannot be used until the cause and extent of damage are determined. If it is the only shaft in the ship, then no mobility is available. In addition to the affects of a typical loss of lube oil casualty, a major lube oil leak sends the ship to General Quarters because of the fire hazard posed by the leak. If actions are taken quickly enough, the extent of damage is minimized and restoration is easier, requiring only correction of the cause and verification that no damage occurred.
2. HOT and UNCONTROLLABLE HOT BEARINGS. Bearing temperatures are monitored closely for an early indication of a problem since the potential damage and subsequent impact of a failed bearing is so great. Bearing temperatures are monitored and recorded hourly by the watch team. Since bearing temperatures vary under different loads, the watch team must be familiar with the temperatures of all the bearings under the different loads. This is not as difficult as it may sound and the logs serve as a ready reference. Generally, a "hot" bearing is any bearing which has a hotter than normal bearing temperature. "Normal" is a function of the load on the bearing, which is function of shaft speed. A bearing is considered "uncontrollably hot" when it reaches 180 degrees F, has a 50 degree rise across the bearing, or is increasing rapidly and cannot be controlled. The actions required vary for these two situations. Beyond these criteria, there are other symptoms of hot or uncontrollably hot bearings: the bearing cover is excessively hot to the touch, babbitt or foreign matter is found in the lube oil strainer, the oil in the sight flow indicator suddenly changes color, an unusual noise or vibration from the bearing, or the bearing is emitting smoke.
a. Common causes for hot bearings are insufficient lube oil pressure to the bearings, dirty lube oil, poor condition of journal surface, obstructed bearing oil supply or return line, improperly fitted or aligned bearing, excessive gland seal leaking past labyrinths, and loss of bearing oil film due to water in lube oil.
b. The first action taken for a hot bearing is to station a bearing watch, usually the messenger. This watch continuously monitors the bearing temperature, notifying the watch supervisor of continuing increases or other changes. Specifically, the bearing watch is looking for a sudden drop in bearing temperature which indicates that the bearing has wiped. This means that the babbitt has been peeled away from the bearing surface, enlarging the oil clearance, eliminating the cause of friction and the increase in heat of the bearing, allowing the bearing temperature to drop. Other actions include checking for proper lube oil system pressure, lowering the lube oil cooler outlet temperature (but not below 120 degrees F), rigging artificial cooling across the bearing cover to help remove heat, and applying wet rags to help remove the heat from the bearing cover (usually a last resort since the water can leak into the bearing contaminating the lube oil). If it is a turbine bearing, gland seal can blow onto the bearing cover or the thermometer, increasing the bearing temperature. Deflecting the gland seal steam can help lower the pressure. The lube oil strainers are shifted and inspected to check for possible causes or damage.
c. When these initial actions cannot control the rise in bearing temperature, the shaft must be slowed. This is done in standard speed increments to remove some of the load off the bearing. In twin shaft ships, both shafts must be slowed to properly unload the affected bearing. The maximum speed available is that which can be maintained without increasing the affected bearing temperature. If the temperature continues to rise or becomes uncontrollable, the shaft must be stopped and locked.
d. If prompt action is taken, the damage may be minimal. If the bearing has wiped, as determined by physical evidence (external bearing measurements with a depth micrometer, or inspection) restoration may take a day or more. If the damage has been extensive or a replacement bearing is not available, it may be beyond ship's force capability to repair, particularly if it is a main reduction gear bearing.
3. HOT LINE SHAFT BEARINGS. A line shaft bearing casualty is treated the same as any other bearing casualty. The criteria for an uncontrollable hot bearing remains the same, however the 50 degrees rise is figured differently. Since a line shaft bearing usually has no lube oil cooler, the rise is measured from either ambient temperature or from the normal temperature for that bearing under a similar load. All other actions are the same. Since the bearing is far removed from the gland seal system, that cause would not be considered. Lube oil system supply problems are confined to operation of the rings or scraper assemblies or low sump levels. Caution: Do not stop the shaft until bearing temperature can be determined uncontrollable to avoid bearing seizure to the shaft journal. When the bearing temperature is determined uncontrollable, stop and lock the shaft.
4. UNUSUAL NOISE OR VIBRATION IN MAIN ENGINE OR SHAFT. As discussed above, this is not always a loss of lube oil situation but follows closely along with it. The two categories for this casualty are those with a metallic noise and those with a non-metallic noise. For a metallic noise, immediately stop and lock. For those with a non-metallic noise, take the actions below. Possible causes for a metallic noise are turbine blade damage, rubbing between the casing and nozzles, or other internal turbine problems caused by material failure or boiler moisture carryover. Serious power train damage often does not sound metallic but requires that the shaft be stopped and locked. Some of these are a fouled or damaged propeller or shaft, fouled fairwater, broken reduction gear teeth, misalignment of bearings, and loose, broken, or missing line shaft bearing cover hold down bolts. These situations require judgement by watch supervisors and EOOWs. Better safe than sorry.
a. Causes for non-metallic noise are a misaligned or damaged bulkhead shaft seal, debris riding against the shaft, damaged attached lube oil pump and torsional vibration (slip‑stick) in the stern tube or strut bearing. The latter is a situation that commonly occurs in colder water. It is the movement of the shaft overcoming the forces of friction which are holding it in place. It is most frequent at low speeds, particularly when testing the main engine. It manifests itself as an extremely loud high-pitched whine. It poses no material problem.
b. The most common cause for non-metallic vibration is a bowed turbine rotor. This is caused by uneven heating of the turbine rotors, particularly the low pressure turbine rotor since it is located directly above the main condenser. This is the reason that the engine cannot remain stationary for long periods of time and the turbines are spun at regular intervals when the condenser is under vacuum. As a reminder, when the main condenser is in operation, the engine must be spun once every three minutes. Based upon the characteristics of each engine, this may not be sufficient, requiring them to be spun more frequently to preclude bowing a rotor.
c. If a non-metallic noise or vibration is detected, slow the affected shaft until the noise or vibration stops. Continue to slow five rpm below the speed at which the noise or vibration stopped. This speed is the maximum speed available until the cause is found and corrected. If the cause is a bowed rotor, other procedures can be taken to more rapidly heat the rotor evenly. Lower the condenser vacuum by securing the first stage of the main air ejectors. This increases the temperature of the exhaust trunk and helps work out the bow faster. Wait thirty minutes for the rotor to heat evenly and then start increasing speed. If the vibration returns, slow five rpm below that speed and continue until the bow is removed.
d. Continuing to operate the engine with vibration or a bowed rotor can damage the labyrinth seals, allowing the oil to become easily contaminated or the gland seal to leak into the space. If the cause of the vibration is from one of the others mentioned above, continuing to operate with the vibration increases the extent of damage to that component.
5. LOSS OF VACUUM IN MAIN CONDENSER. When the main condenser vacuum starts to drop below normal, which is usually 28-29 inches of vacuum, the watch team starts to take action. Once the condenser has been verified not to be "hot," an investigation for the cause is started. Items checked are: make-up feed tank levels (since a low tank level may allow air to be sucked into the condenser), condenser hotwell level (too high and there is no room for the vacuum, too low and there may be no condensate providing a seal), the loop seal from the air ejector condenser may be lost (allowing air to be sucked into the condenser), there may be an air leak in a fitting under vacuum, the condensate or air ejector condenser temperature may be too hot inhibiting the vacuum, there may be insufficient air ejector motive steam, there may be a problem with gland sealing steam, the main condenser tube sheet may be clogged and the main circ water pump may not be operating properly or not even started.
a. As the vacuum drops, the engine is slowed. When vacuum reaches 21 inches, speed is slowed to two-thirds. At 18 inches, it is slowed to one-third. At 15 inches, the throttle is shut, stopping the engine (note that this is not the same as "stopping and locking" an engine). If vacuum drops below 15 inches, the engine is secured, meaning that vacuum is broken. Continue to investigate for the cause.
b. Securing the main condenser includes shutting the throttles, shutting the main air ejector condenser condensate discharge valve, shifting condensate recirculation from low to high, shifting auxiliary exhaust from the main condenser to an auxiliary condenser (or cross-connecting it), securing steam to the main air ejectors and gland seal systems and eventually placing the engine on the jacking gear. These procedures ensure all heat sources are removed as soon as possible, protecting the condenser tubes, minimizing damage and preventing bowing of the turbine rotors.
6. HOT CONDENSER. As stated above, the criteria for a hot condenser are: main condenser inlet/outlet header temperature in excess of 140 degrees F or a header is hot to the touch. A hot condenser usually is caused by insufficient circulating water flow through the main condenser for any number of reasons: an air bound condenser, failure of the main circ pump or not even starting it, a clogged tube sheet, inadequate heat transfer because of build up on tube surfaces (such as would occur if passing through a large oil slick) and improper securing of the main condenser.
a. A hot condenser is a serious casualty with potential for great damage. Overheating the condenser tubes can cause them to distort and leak, contaminating the condensate with seawater. This damage may actually cause tube breakage. If the rubber expansion joints overheat and then are suddenly cooled, they may rupture and flood the space. In any case, the condenser must cool slowly, taking several hours.
b. When a hot condenser is detected, shut the main engine throttles, secure the main engine by breaking vacuum and removing all heat sources, isolate the condenser by shutting the main condenser overboard valve (in some ships the inlet valves are shut also) and opening the condenser header vents. These procedures help the condenser cool down slowly. CAUTION: Do not attempt to restore circulating water flow through a hot condenser with the main circulating water pump until the condenser cools.
7. JAMMED THROTTLE. The linkage assemblies used to control main engine throttles sometime fail, one of the reasons why the engine is tested before getting underway. Although termed a "jammed throttle," this casualty includes situations when the throttle can be turned but cannot control the throttle assembly. The most common causes of this casualty are broken pins on the linkages, jammed gears, cams or springs on the linkages, foreign material caught between the nozzle valve seat and disk, bent or damaged throttle poppet valves, and failure of the remote throttle assembly (which is installed in some ships). Of all these, sheared pins on the linkages are the most common cause.
a. While control of the throttle is lost for any of the above reasons, the speed of the engine cannot be controlled with the throttle valve. The engine can be slowed using the main engine guarding valve, but speed cannot be increased without taking some other action. This means that the maximum speed available is the speed where the valve jammed.
b. The main engine guarding valve is shut until steam chest pressure and engine speed decrease slightly, demonstrating that they have control of the ship's speed with the main engine guarding valve. At this point, the speed can be slowed and the investigation for the cause can continue. Once detected, the cause is repaired and the throttle tested. Repairs are often completed in less than thirty minutes.
D. SUMMARY
Main Engine casualties can have significantly damaging consequences. Watchstanders shall be fully trained to respond to parameters and indications to prevent further damage to equipment by initiating immmediate and controlling actions. While this training requirement reduces instability in plant operations, danger lies in the neglect for consideration of ship’s manuvering. This oversight could produce catastrophic results in restricted manuvering situations. Plane guard, alongside replenishment, and other special manuvering combinations already have the potential for ship hazarding. Every member of every watch team should have thorough knowledge of casualty control procedures and those enginering instructions, notes, and standing orders that address response during manuvering situations.