_INFORMATION SHEET

INFORMATION SHEET

TURBINE/GEAR MAINTENANCE

Information Sheet Number 62S-103

INTRODUCTION

The Main Engine and Reduction Gears are two of the most simply designed pieces of equipment in the propulsion plant. Although their design is simple, they are two of the most important pieces of equipment on board a ship. Without the main engine and the reduction gears a ship is unable to get underway or maneuver. The maintenance and thorough monitoring of these components are paramount to safe and prolonged operation. There is nothing that can be done to an operating engine and reduction gear while operating other than to maintain the lube oil's cleanliness and to monitor and record the various readings taken. These readings are the key indicators used to determine what maintenance is required and needed.

1. Information in this student guide complements MRCs, information in NSTMs and manufacturer's technical publications.

2. Where PMS coverage applies, preventive maintenance will be accomplished in accordance with MRCs. The MRC supersedes all other procedures. It should be noted that PMS is the minimum required, the Engineer Officer can always demand more, but PMS is very detailed and precise throughout the fleet on main engine maintenance.

3. NSTMs, manufacturer's equipment manuals, ship's information books, blueprints, and applicable documents (TYCOM maintenance manuals/instructions, etc.) will provide detailed procedures for maintenance, inspections and tests.

4. These publications also provide information for the evaluation of tests and inspection not covered by MRC's.

REFERENCES

(a) Reduction Gears Technical Manual NAVSEA 0951-LP-022-6010

(b) Propulsion Turbines NSTM Chapter 231

INFORMATION

A.PURPOSE OF MAIN ENGINE/REDUCTION GEAR MAINTENANCE. The maximum operational reliability and efficiency of an engineering plant requires a planned program of inspections, not only to discover parts that may fail at a critical time, but to eliminate underlying conditions such as misalignment, corrosion, erosion and improper fabrication.

1. RESPONSIBILITY OF THE ENGINEER OFFICER

a. The Engineer Officer's knowledge and supervision directly affects this program of inspections and maintenance. He/she must insure that the proper techniques were used and that the data derived from the inspections are properly interpreted.

b. Engineering maintenance is the coordination of many parts; technical knowledge, i.e. corporate knowledge and technical skills of personnel, (PMS) and of course publications and references.

c. Engineering planned preventive maintenance has been formalized but it must be understood that this program is only the minimum requirement.

d. An Engineer Officer should have an in-depth understanding of the PMS requirements and insure supplemental maintenance is accomplished to insure equipment reliability and safe operation.

e. Training should also be considered as part of a proper engineering maintenance program. The training should not only include proper maintenance procedures but also information that will insure that the equipment is operated under the proper procedures and parameters.

2. TURBINE MAINTENANCE

a. NSTM Chapter 231 Propulsion Turbines is the "bible" for all maintenance actions, inspection procedures and casualty control procedures for main turbines. Taken from the NSTM is a table showing turbine maintenance items and the purpose for each. Periodic tests and inspections have been developed that will insure the items listed are covered (see Figure 1).

MAINTENANCE ITEMS AND PURPOSE TABLE

ITEM	PURPOSE
Verification of radial and axial position of the rotor by appropriate clearance methods	Avoid internal rubs that can make equipment inoperable
A clean lube oil system and the proper lubricant quality and quantity	Avoid wiping of bearings, scoring of journals and thrust collar and chemical attack on those and other critical surfaces
Freedom of turbine controls	Avoid slow action or hag up of throttles
Check condition of oil deflectors and waste oil drains	Avoid ingress of oil into steam system
Check condition of water drains	Avoid ingress of water into lubricating systems, blade erosion and water slugging
Check cleanliness of machinery internals	Avoid ingress of foreign material through access openings or through connected piping, which restricts internal damage (mechanical or chemical)
Check condition of shaft and gland packing	Avoid blowing steam into engineroom or pulling air into turbine or condenser

Figure 1

PERIODIC TESTS AND INSPECTIONS

TESTS/INSPECTIONS	FREQUENCY
Operate LO purifier while underway	Daily
Operate and lubricate all valve operate linkages	Monthly (if secured)
Take micrometer readings on the journal bearings of the main propulsion turbines	Quarterly
Lift sentinel and relief valves by hand	Quarterly (some platforms are semi-annual)
measure main turbine thrust clearance	Annually
Inspect interior of turbine casing	Regular overhaul or if damage is suspected
Clean, inspect, interior of turbine casing	Regular overhaul cycle
Inspect main propulsion bearing journals and oil deflectors measure clearances	Annually and regular overhaul
Inspect shaft packing and journal for condition, check clearances	Regular overhaul cycle
Foundation bolt tightness	Regular overhaul
Drain and refill operating control gear boxes	Annually and regular overhaul
Remove and clean main steam strainer	Regular overhaul
Measure nozzle clearance	Regular overhaul
Test high and low pressure turbine sentinel valves	Annually or regular overhaul

Figure 2

a. The next table (see Figure 2) lists periodic tests and inspections for a turbine. This is a sampling of items and all of these items are covered under the PMS system.

b. Propulsion Turbines are basically designed machines. The dynamic loading and transient conditions applied to main turbines make the inspections and maintenance vital to safe and prolonged operation. The main engine is always in operation while underway, unless a casualty occurs. The only time preventive maintenance can be completed is inport, with the engine secured. Through proper scheduling, a majority of the required maintenance can be accomplished at the same time. This should give the Engineer Officer and MPA a "warm fuzzy", as they will be aware of the exact status of the main engines, including all of the measurements and clearances. This information can be vital to the Engineer Officer if a casualty occurs.

c. The Engineer Officer will find very few actions that ship's force can do to a main turbine. The review of operating logs and the maintenance of clean lube oil are the best things for the turbine. The actual inspection of the turbine internals and casing is performed by the Engineer Officer using the MRC. Prior to the inspection, the Engineer Officer needs to review the MRC and NSTM 231. These documents aid the Engineer Officer in the inspection and assists in the recording of the material history by using standardized terms.

d. During the inspection, the Engineer Officer is only able to see about 10-25% of the HP turbine internals and 40-60% of the LP turbine internals (see Figure 3 as a guide). Access ports allow viewing of the 1st stage area, the exhaust end of the HP and a view of the balance weights. The access ports at the steam inlet or first stage are very small and provide a limited amount of area to be seen. This is due to the casing halves being together and the turbine internals obstructing some of the view. A borescope can be useful in this area, if one is available. The access ports on the LP turbine are considerably larger and provide a more extensive look inside. The major areas that can be observed are the astern elements, the exhaust of the LP and astern elements and the diaphragms and supports.

TURBINE INSPECTION GUIDE

TURBINE PART	LOOK FOR THE FOLLOWING
Interior surface of casing	Corrosion, erosion, condition of casing steam seal surfaces
Nozzle diaphragms	Erosion/corrosion of horizontal parting and vertical steam seal surfaces, condition of radial/axial crush pins. Erosion/corrosion pitting and cracking of vanes
Diaphragm and gland packing rings (carbon and labyrinths)	Wear, freedom of movement, condition of springs, position relative to the rotor
Rotor blading and shrouding	Cracks, dents, tears, erosion, corrosion, lifting of the shroud, integrity of stellite shields, axial and radial rubs
Rotor	Surface cracks of chromed or spray metalled areas. Balance weights intact and firmly anchored. Erosion/corrosion of packing areas and integrity of end plugs on hollow rotors. Journal condition (scoring, wear, pitting) Thrust collar (scoring, wear, pitting, tightness)
Journal Bearing	Wear, loose babbitt, contact pattern, scoring, tin oxide, RTE intact
Thrust Bearing	Shoe wear, loose babbitt, contact pattern, scoring, wear of leveling plate supports, RTE intact
Blading radial seals	Wear, pieces broken out, firmly seated
Horizontal joint (main and nozzle chest)	Steam cutting, evidence of leaks
Casing structure	Cracks in casing, particularly in the HP first stage shell area and floor of main steam chest. Cracks in casing support plates, welds, flex, plates. Proper clearance for and freedom of keys and sliding feet. Distortion of gland housing.
Valves (nozzle, bypass transfer, extraction and drain)	Scoring of lift rods in way of bushings. Condition of stems that may indicate leakage or hang up. Wear of linkages, bearings and cams
Rotor position differential expansion indicators	Wear, adjustment, calibration
Nozzle blocks	Cracks in ligaments between reamed nozzles. Both retainer plates out of position. Loose or broken bolts

Figure 3

a. Three things can be useful to the Engineer Officer during a turbine inspection: the use of Morpholine or a corrosion inhibitor when operating; reviewing of the operating logs and knowledge of where damage is most probable. Morpholine or some corrosion inhibitor is carried over in the steam supplied by the boiler. This "coats" the piping and equipment internals. These components become either a light gray or brownish in appearance. The Engineer Officer should be looking for a difference in color. Cracking, erosion or corrosion affect this protective layer and the color will appear different. The Engineer Officer should be keying in on this, as it is hard enough to see the turbine internals. He or she should be aware of this fact and how it will help them. Also, the use of corrosion inhibitors has greatly reduced the problems encountered by corroding materials and this problem is almost non-existent now.

b. The review of operating logs against design limits provided in the main engine technical manuals can help identify possible steam flow problems. Abnormal pressures and temperatures can be used to highlight suspected problem areas. If journal bearing clearances are satisfactory, there should be no problems in the turbine's steam flow. The flow design of the turbine is dependent on the alignment provided by the bearings.

c. The probability of damage or wear is greatest where the highest pressures and temperatures occur. This area is easy to find; the HP first stage and nozzle block (the small access ports allow viewing this area) and the astern elements of the LP turbine (large access ports show this). If there is no damage in these areas, it is a safe bet that the rest of the turbine is okay (as each stage of the turbine there is a pressure drop and temperature is decreased). This area should be of primary interest to the inspector.

d. Important considerations behind the requirements for turbine PMS are maintaining the design steam path clearances and insuring proper axial and radial clearances. As stated earlier, operating logs can be very useful at this point. The two components used to maintain alignment are thrust bearings and journal bearings.

e. Axial clearances are designed to allow for turbine rotor/casing expansion, contraction, and movement. This movement is limited by use of a Kingsbury type thrust bearing on most platforms. Axial clearances can be checked both during operation and when the turbine is idle by using the rotor position indicator. This reading provides a "quick look" or reference of axial alignment.

f. Radial position and alignment of a turbine is maintained by the use of journal bearings. Excessive wear or damage to journal bearings can cause extensive problems inside a turbine, much more than average problems experienced by a damaged thrust bearing. The thrust bearing's maximum clearance is only half the distance between the casing and blading, this allows some safety margin. Once the journal bearing is damaged, the shaft "drops" and rests on the internal components (gland seal and diaphragm labyrinths). This damage affects the seals and steam flow through the turbine. Watchstanders might find this by their hourly readings. If you notice an increase in gland seal steam, blow by of steam from the glands or slightly abnormal bearing temperatures, you should investigate. It is important to realize, that once the internal labyrinths are damaged there is generally little you can do. The ship's force, on most platforms can only change out or repair the outer set of labyrinths, because the turbine casing allows no access to the others. Maintaining the radial position of the turbine and reduction gear components within design limits prevents damage to:

(1) Turbine casing

(2) Turbine blading and shrouding

(3) Turbine diaphragm and packing rings

(4) Turbine oil deflector rings

(5) Reduction gears due to mis-alignment

g.. Propulsion turbines are balanced to a "T" prior to assembly in a ship. As long as all operating parameters are within specifications, the turbine will last for a long time. If something goes wrong with a turbine, sight and hearing will probably be the first indication of something wrong. Your watchstander is the first line of defense. Does he or she know this?

h. The way a turbine is operated can affect the maintenance and reliability of the turbine. A rotor should never sit still for more than 5 minutes after steam has been admitted. If a turbine in operation should suddenly vibrate, the problem could be any one of the following:

(1) Water in the turbine

(2) Bearing failure

(3) Bent or broken propeller blades

(4) Unbalance due to broken or missing rotor blades

(5) Rubbing of blading labyrinth packing or seal rings

(6) Bowed rotor

i. If you hear a rumbling sound and the turbine begins to vibrate, it is probably water or foreign material. But it is important to know that vibrations or noises from either the turbine or shaft can travel to the reduction gears. This greatly affects the watchstanders in their troubleshooting.

j. Sometimes the Engineer Officer might feel an internal inspection is needed if the noises or vibrations were excessive (prolonged operation while bowed or with an excessive vibration can be a contributing factor). A sure sign of something rubbing on the rotor will be a shiny spot on the rotor (that difference in color again). If this is noted during an inspection, immediately investigate the cause and correct it.

k. When rubbing of a turbine blade or labyrinth occurs, the cause will probably be a bowed rotor. Other causes could be:

(1) A defective thrust bearing (usually noticed in an RPI reading)

(2) A wiped journal bearing (possible problems with gland seal steam)

(3) Foreign material inside the casing (Equipment close-out sat?)

(4) Differential in the amount of expansion between the casing and the rotor (proper warm up of the turbines can prevent this)

l. A lot of these problems are preventable by operating safely in accordance with EOSS. The satisfactory operation of a turbine depends largely upon the axial and radial alignment of the rotor in the casing. During normal operations, the temperature of the oil leaving the bearing is the sole criterion available to the operator for judging the conditions of the various bearings. Oil temperature leaving a bearing will vary depending on the changes in speed, especially since all turbine and reduction gears are sliding surface contact bearings. These bearings develop a lot of heat due to friction and are dependent upon proper quantity and quality of the lubricant. Thus, keeping the lube oil quality at it's best is vital to prolonged operation. Over a period of time you should be able to chart the changes and detect any bearing that may be out of specifications (reviewing of operational logs again).

m. If it is suspected that one of the bearings is out of specifications, when the turbine is secured you can take a "quick look" at the bearings. A depth gage is the quickest and easiest means to determine the amount of wear on a journal bearing. When a bearing is first installed, make a measurement on the bearing to act as a base point. Log this reading. This is your reference point. Never make repairs to a bearing solely upon the outcome of a depth gage reading. If a depth gage reading shows up bad, then make other measurements to the bearing before trying to make repairs.

n. If other measurements are required besides a depth gage, then the bearing will need disassembly and inspection. Some journal to bearing rubbing contact is made on each start. A good bearing will show a polished area centered in the lower half of the bearing. Discoloration of bearing surfaces almost always indicate a lubrication problem. Moisture in the oil and operation under high temperatures can produce a tin oxide coating on the bearing. This coating is very hard and builds up to reduce bearing clearance.

o. If a bearing is to be replaced, ensure the spare meets all the design specifications prior to reassembly. When removing an old bearing, do not lift the rotor more than .005 inch. Lifting the rotor too much will damage the shaft packing. The new bearing must be reassembled properly. You can put a bearing in backwards. This could lead to another casualty due to lack of lubrication.

p. The easiest way to measure the axial clearance is by the installed Rotor Position Indicator. Another means would be to position a dial indicator against the rotor and jack the rotor fore and aft three times, using the average of the three. If there is an indication of a worn thrust bearing, then remove the cover to the bearing and make a feeler gage measurement of the bearing. If a bearing needs to be repaired, then repair all surfaces, make new measurements and shim the bearing to ensure it meets all specifications on oil clearances.

q. Most inspections of the turbine internals will be done through access covers. there are two times when you would remove the turbine casing. The first is when there is knowledge or suspicion of internal damage. In this case you should get technical determination of the necessity to disassemble from NAVSEA. NAVSEA will review your operating logs, take their own readings to discover what is going on with the turbine and its' internals. The second time would be three months prior to overhaul and then NAVSEA will again repeat the process to see if lifting the casing is absolutely necessary. Submit a report to the type commander about the condition of the turbine. In both situations the type commander should be aware of the condition of the turbine and will make the final authorization, after he has all the information, to lift the casings. If it is not absolutely necessary, an alternate maintenance action will take place due to the cost of lifting the turbine casing.

r. Whenever there has been a main propulsion turbine opened for repair or inspections, the work is not complete until a dock trial and post repair trial has been satisfactorily completed. The Engineer Officer of each ship will issue instructions for operating the plant during a dock or post repair trial.

s. The trial will go something like this. Install muslin bags in the lube oil strainers and determine the frequency to which these are to be changed. Once the muslin bags are found to be clean, then engage the jacking gear. Station personnel around the turbine to detect any unusual conditions or noises. If none exist, then consider the turbine ready to do a dock trial.

t. For the dock trial the Commanding Officer will determine the maximum number of RPM's he/she wants the shaft to go. The Engineer Officer determines the amount of time needed to warm up the main engines and when ready, notifies the OOD. The bridge determines the number of RPM's and slowly increases to the maximum RPM allowed. If there are no difficulties, then the turbine would be ready for a post repair trial.

B.MEASUREMENT METHODS FOR TURBINE/GEAR BEARINGS

a. Journal bearings can be measured in a few ways. these are the ways available to determine bearing clearances:

(1) The Depth Micrometer Method. This is the quickest method to get an indication of ring wear. These is no disassembly of the bearing. The turbine must be isolated and secured from rotating and the lube oil system must be secured for at least 24 hours prior to taking the measurement. NOTE: This method is only a quick check and should not be used as a final method of determining bearing clearances.

(2) The Bridge Gage Method. This method requires the component to be placed out of commission and disassembled. It is used when there is no access for a micrometer in the bearing. This requires two personnel to perform and is not as accurate. Only a few ships use as the method for taking measurements.

(3) The Crown Thickness Method. This method requires disassembly of the journal bearing. The bearing is rolled out of the component and a micrometer is used to take readings of the bearing thickness at scribed lines on the side of the bearing shell. A drill bit or round object is needed also. The micrometer has a square face and the bearing shell has a rounded shape, the drill bit allows the measurement to take place.

(4) The Leadwire/Plasti-gage Method. This method requires the component to be placed out of commission and disassembled. Leadwire/Plasti-gage method is used primarily on spring bearings which do not have a bridge gage assembly or access hole for a depth micrometer and because of the size and location of the spring bearings.

(5) The OD and ID Method. The bearing is disassembled and the inside of the bearing is measured. The outside of the shaft is measured. The clearance is the difference between the two. This method is very accurate, allowing the bearings wear pattern to be checked. It is recommended to go from a depth micrometer reading to this method as final verification of readings.