Document V338XNYao3eE3vYpBjVm1xo7g

Harold J. Chastr EIGHTEEN years' experience in designing and in stalling turbines for marine and central station use is the record of Harold J. Chase of the Federal and Marine Department of the General Electric Company. Mr. Chase was born in Woodbury, New Jersey, but he received his education in Portland, Maine. It was in Portland that he developed a seagoing urge which he satisfied, after graduating from high school, with some real blue-water sailing. The high point of his sea experience was the turn he served as quartermaster on a freighter going to the English Channel and North Sea ports. In July, 1924, immediately after graduating from the University of Maine with a degree of B. S. in Mechanical Engineering, he joined the Test Course of the General Electric Company and went to work on turbines. His broad knowledge of propulsion turbines, gained from first-hand field experience, makes him well qualified to write on their maintenance. ^PING smPSH4pc SKILFUL UPKEEP OF PROPULSION TURBINES 2nd Article of a Series By Harold J. Chase HE first requirement presented Tto the operator of a turbine is to keep the machine ready to meet- a load schedule. This involves mainte nance, and the best way to assure good turbine maintenance is to set up a sys tem for regular inspection. This should establish a routine to be followe v dicate when and what correctin' ad repairs are made, and schedu.. -wrections that need to be made. Of course, the character of the load sched ule dictates the details of routine main tenance. With today's stepped-up shipping schedules keeping propulsion turbines humming there are many things to do during normal operation as well as during the out-of-service periods, that will contribute to smooth, trouble free service, and maintain high quality performance. 'I'o extract the last bit of power from each pound of steam, turbines of all kinds depend on the accurate guid ing of the steam How. Essentially, this demands that the steam be con fined to the smooth paths of the nozzles and buckets which have been carefully Nozzles end buckets similar to these guide the steam smoothly designed 1 the turbine builder, and that waste flow along the shaft be cut down by well-designed and close-fit ting packings. One of the worst enemies of good turbine performance is distortion of the parts. This can result in all man ner of trouble, from the loss of effi ciency due to increased clearance, up to conditions where full power opera tion cannot be obtained because of permanent damage. Such distortion may come from misalignment, uneven heating of parts, or wear on some parts. In some cases, misalignment may be due to connections to the turbine. For example, while foundations are ordinarily adequate, the uneven move ment of supporting columns may cause trouble. Escaping steam from a joint or connection, loosening of heat lag ging from a pipe near a beam, or emergency operation under reduced vacuum, may cause change in position of the turbine base. Such things, however, are ordinarily easy to find and correct. Uneven heating of parts in the tur bine itself is sometimes more difficult to deal with. The'natural flow of heat in a turbine shut down after some hours running causes the rotor and casing to distort. Such distortion is most pronounced in the first hours after shutdown. To avoid this diffi culty, many turbines are equipped with turning gears. This equipment con sists of a small motor with large gear reduction, which is connected to the turbine to keep it turning slowly dur ing cooling down and warming up periods. Regular and consistent use of the turning gear will mean easier starting of the turbine; prevent pack ing rubbing; and result in better preservation of the close shaft clear ances necessary to good economy. For turbines that are not fitted with mo tor-driven turning gears, it usually is possible to contrive some connection to the shaft to rotate it about half a turn every ten or fifteen minutes. Such a substitute is effective in keeping the shaft straight. Uneven heating of the turbine due to steam escaping into the machine by way of a leaking valve in an extrac tion or drain line is a common source of trouble. Such flow of vapor into a turbine during shutdown may also cause corrosion. Valve leakage can often be detected by noting if the pipe connections re main unduly warm when the turbine A typical motor-driven turning gear for a turbine-gear propulsion unit Reprinted from the August. 1942. issue of The Nautical Gautic is shut down. Operating the air pump daily during shutdown also helps dry out the machine. Wear, as affecting distortion, is not usually very important and also is much less likely to occur in average turbines. Such things as wear on flexi ble couplings is brought under con trol by attention to lubrication. The same is true of bearings. It is usually possible to inspect such parts often enough to detect undue wear and make corrections. Another operating problem that can have serious effects on the turbine is carryover ir *he steam. While mod em boiler operation is ordinarily en tirely satisfactory from this standpoint, it sometimes happens that the situa tion gets out of hand. Carryover into the turbine in the form of boiler compound, for example, can cause trouble by sticking the valves and can reduce the output of the turbine bv its effect on the blades. This is a re sult of reduction of area of the nozzles, which is revealed by increasing tur bine stage pressures, particularly in the high pressure end. One short and general precept which applies to the whole problem of up keep is to prevent repairs by keeping things clean. This applies, of course, to strainers, since oil, water, and steam strainers should be inspected frequently to insure that they are clean. Such points as governor levers and joints and valve sliding parts obvi ously must be kept clean, and should be greased or oiled as directed by the manufacturer's instructions. The in terior of casings sometimes can be inspected through inspection coven. When regular inspections are made, oil sludge and corrosion can be caught and the cause found before serious ent installations vary, it is impossible to set up a schedule that will meet the maintenance requirements of every in stallation perfectly. For example, cross compound turbines on a reduction gear equipment present a different set of requirements than a single casing tur bine used with electric propulsion. Governor end confcol-vslvt llnkefe as In stalled on twbine-electric propulsion unit trouble results. Items, such as oil or water seepages and drips should be repaired promptly, for although the loss or leak may not appear important at its source, such drips, especially of oil, may seep into pipe covering, or electrical apparatus, thus causing a fire hazard. Because the requirements of differ However, the general form shown here cross-indexes the points common to all types of turbines which should be included in the schedule for a daily check while under way. Normally, if the engine room watch takes rec ords of the usual steam gage readings and also the normal lubrication oil pressures and temperatures, they will show if any particular change is tak ing place in turbine performance. How ever, these records cannot tell the whole story. The most thorough prac tice is for some engineer other t' a the watch to make the regular in- > tion according to a daily schedule ...et which can be signed and used as a record of the examination and the needed and executed repairs. Here is a list of some of the im portant things to be considered in making the regular inspection: 1. General Cleanliness Note particularly any leakage of steam, oil, or water. This should in clude also looking for any pipe cover ing becoming oil- or water-soaked. 2. Smoothness of Operation Any unusual vibration or noise should be investigated and the cause Diagram for use with "Daily Maintenance Chart" on next pase DAILY MAINTENANCE CHART CHECK LOOK FOR Main Turbine 1. For'd End Aft End Rotor Position 2. Trip Valve 3. Control Valve 4. Extraction Valves 5. Oil Pumps (Stand-by) 6. Oil Alarms 7 Oil Strainers 8. Steam Seal System 9. Thermometer and Gage Connections O 3 6 V V </ V found. It may be a perfectly normal consequence of changing draft of the ship or the result of sea conditions. /" I I 3. Gage*, Meters, and Thermometers Indicating instruments should be checked to be sure that they are in service as intended. Make sure that their sockets or bosses in casings or pipes are well secured, and that there is no vibration either of the gage needles or of the connecting piping. 4. Lubricating Oil Systems An examination of the lubricating oil systems should include particular attention to any foaming or sludging or variation in normal oit levels in the system. It is sometimes helpful to draw off a small sample of oil from the sump tank to see if any sludge or water has settled there. Section of bearing ^ assembly, showing ar rangement. of ther mometer and bubbler for observing condi tion of lubricating oil -5- Steam L e d ^ Oil Levels and Foaming / f t T \ Test Operation S< Throttle Trip Valve The throttle trip valve should be clean, particularly the stem and the guides to insure that it is free to act. Ordinarily it is possible to close this a few turns momentarily by means of its hand wheel to be sure that the valve stem moves freely. 6. Main Control Valvea and Governor Parts These should be kept cleaned and oiled and the moving parts examined for wear, binding, or lost motion. 7. Automatic Standbys >/ Where automatic standby equipment J is used, a check should be made of the V automatic features to insure that the equipment will come into service when required. For example, if an auto y/ matic standby lubricating oil pump is used, a test should be made to see that </ the pump starts and begins to deliver oil in response to its proper signal. io --m 8. Alarm Signal* In addition to automatic standby equipment, there are often alarm sig nals to indicate such things as low lubricating oil pressure. The opera tion of this alarm system and similar ones should also be tested. 9. Strainer* For continuous duty service such as lubricating oil systems, strainers are usually fitted in pairs such that one can be removed and cleaned while the other is in service. Certain cooling water lines sometimes have similar strainers. The regular watch should have a routine for cleaning all strainers to be sure that a clean strainer is al ways ready for service. 10. Steam Sealing Syatem During long voyages, the steam seal ing system may not be called on to change its action for long periods. This may result in setting of the valves or wear at some particular point on the valve stem. Automatically controlled sealing systems should be checked to make sure that the valves move freely through the full range. Major Irupeelions Once a year the turbine should be completely dismantled for a thorough examination. Services of the shipyard maintenance crew and the turbine manufacturer's engineers are custom arily called upon for these major in spections, and the extent of the main tenance necessary then will be in pro portion to how well the daily job has been done. As part of the major inspection, all valves admitting steam to the tur bine should be tested to be sure that they close tightly. Main control and throttle valves, as weJJ.as drain valves and extraction valves can be sources of trouble if they do not seat properly. While the turbine is open, a complete clearance check should be made. This should include axial as well as radial clearances, especially around the shaft packings. At the same time, relative readings on the rotor position indica tor and, if possible, the clearance in spection opening should be examined Shaft-padcins and carbon rinfi art part of tho ataaaa-aaallnj ayitam to be certain that these external clear ance indicating points are giving a true picture of the interior clearances. All blading should be examined very carefully for signs of deposits and also for water cutting. Deposits probably will be localized in the high-pressure end of the machine, where corrosion due to impurities in the steam may also be found. Water cutting, of course, is present only in the lower stages of modem high-temperature machines and here the water drainage systems from each stage should be checked. The interior of the exhaust casing and the condenser tubes, if close to the last wheel, should be examined to see if water thrown off the last stage is impinging on them. On a geared unit, the astern element should be checked for signs of steam leakage past the astern valves. All interior joints of the turbine, such as those of the stage diaphragms, should be examined for signs of leak age. Leakage may also occur through ihe packing rings, especially through high-pressure packing rings. Where packings depend on springs for fit, the springs should be checked to be sure that they are still strong enough to hold the packings in place. --6-- SOME OF THE IMPORTANT POINTS TO BE CHECKED DURING A MAJOR OVERHAUL OF A PROPULSION TURBINE (a) Hi|h-prriiurf buckets Scale may be found here. If it is, it can sometimes be removed by wash ing with water. Some scale must be scraped off mechanically--with emery paper or, if available, fly-ash. (b) Low-pressure Buckets Water cutting may have occurred here particularly at the entrance edges near the bucket tips. If they are deeply eroded, it may be necessary to install new buckets. Amount of the errosion which can be measured by using a straight edge and a feeler gage, should be recorded for comparison at the next inspection if the buckets are not re placed. (c) Water Drainage Orifices If the low-pressure blades have sus tained severe water cutting, these ori fices will probably be found to be plugged so they do not drain properly. The orifices should be cleaned out thoroughly to prevent water from backing up and causing further cutting of the buckets. (d) Diaphragm Joints Leakage across these joints may be taking place. Flow marks will be evi dent if it is. Such leakage usually means that the diaphragm is not prop erly seated, or that a new joint key is needed. (c) Rotor Clearance This should be measured and checked against the manufacturer's original tolerance. If necessary, clear ance of the rotor is adjusted by means of shims locating the thrust bearing. (f) Beating Clearances If the clearance of the bearings is greater than the manufacturer's tol erance, the bearings should be rebab bitted or spares should be installed. (g) Packing Rings Excess leakage may be taking place if the packing clearance is consider ably greater than the manufacturer's tolerance. In this case it will be neces sary to refit the packing or install new packing to restore the original clear ance. (h) Casing Interior and Condenser Tabes If errosion is found here, it may be necessary to install baffle plates to pro tect the erroded parts, which sometimes can be metallized to restore as well as protect their surface. -7- 1 I PROPULSION TURBINES AND GEARS KJEFEJU-NCB August, 1940 To Marine Equipment Salesmen: Begun four years ago, the greatest boom in shipbuild ing since the first World War is continuing now at a still faster pace. Our orders for turbines and gears during the first six months of 1940 totalled more than 800,000 horse power for 26 Navy and merchant vessels, including a superbattleship, light cruisers, destroyers, and a mine layer. Equipments ordered for merchant ships represent an increase of 144 per cent over orders for the first half of 1939. This bulletin reveals the important part we are tak ing in this program and shows some of the new manu facturing methods and equipment we are using to meet the situation. MANAGER/ Federal and Marine Department iCM r "ler- v;. PROPULSION TURBINES AND GEARS STEAM PROPULSION EQUIPMENT consists of high-speed, efficient turbines, generally of the cross-compound type, and double-redaction gears. The ahead turbine has a high-pressure and a low-pressure unit in series. The astern turbine has only a few stages, is located in the low-pressure cas ing, and develops from 30 to 40 per cent as much power as the ahead tur bine. . Gear reduction may be as high as 70 to 1. On merchant vessels, mostly tankers and cargo ships, the gears are conservatively rated as*the ships operate continuously at full power. Gears on naval vessels are more liberally rated because weight reduction is more important and they seldom operate at full power. 7*7 7r Fig. 2 - Merchant vessels are nsnally single screw and have turbines from 3000 to 12, 000 bp. Gears are of the M. D. type with two pinions driving the low-speed gear. TURBINE ---------- f H.P. TURBINE Fig. 3 - Cross-compound turbine generally used with double-reduction gears (not shown) for merchant ships. L.P. TURBINE Fig. 4 - Destroyers are twin screw; cruis ers and battleships have four screws. Each screw is driven by turbines above 25, 000 hp and has MDT type gears with four pinions driving the low-speed gear. H.P. TURBINE PROPULSION TURBINES AND GEARS Fig. 5 (right) - G-B doable redaction genre Type MDT-8S- A for naval vessels and Fig. 6 (below) - with cover removed. /67FZ/ TURBINES for naval vessels are usually built at Schenectady; turbines for merchant ships and all reduction gears are built at West Lynn. Because of the business upswing and an increase in the number of fabricated parts, ad ditions to thefabricating shop at Lynn and installation of more annealing ovens was necessary. Fig. 7 - Arc-welding the low-speed gear lor a Gull Relining Co. tanker. This is typical o1 labricating done at Vest Lynn, as is... PROPULSION TURBINES AND GEARS '7J-?sZ Fig. 8 - ...this center section of a donble-rednction gear casing -- being lowered into an annealing fnrnace after welding. ^ Fig. 9 - Propulsion turbines now have solid rotors -- wheels integral with the shaft -- like this low-pressure rotor for a cross-compound turbine. Lathes have been added to turn these large forgings. Fig. 10 - Machining a low-speed gear on a 20-ft vertical boring mill at Lynn. This giant and a 14-ft unit have been in stalled for boring -low-speed gear hnbs and for turning gear webs and tires. PROPULSION TURBINES AND GEARS '/WtXt f Pig- 11 - Two large horizontal boring mills have been installed for accurately machining gear casings with their numer ous bearings. Fig. 12 - Quality and accuracy, for quiet operation, are built into G-B gears in this modern temperature-controlled build ing which houses such equipment as... Fig. 13 - ... this new 200-in. hobber (and another now under construction) as well as the 165-in. bobber, 200-in. gap lathe, and... PROPULSION TURBINES AND GEARS _____________ _________________________ Fig. 14 - ... this dy namic balancing ma chine lor large gears, and contact stands lor improving the tooth contact. THE 200-in. HOBBEKS were built by General Electric because no manufacturer of gear-cutting equipment would meet our rigid requirements except at an exorbitant price. The excellent gears that hare been cut on the new hobber justify the decision to build our own equipment. PROPULSION TURBINES AND GEARS TESTING FACILI TIES have been added to keep pace with the improved manufactur ing equipment* New boilers installed re cently will enable us to operate turbines under contract steam c onditions. Fig* 16 - Four stands like these are available for assembling and testing tnrblne-gear sets -- usually formerchant ships. The sets can be loaded up to about 8000 hp with the generators provided. Reduction gears for naval combat ships, and other gears not assembled with their turbines, are tested "back to back" by special torquing devices to obtain full-load tooth pressures. Fig. 17 - For testing gears in pairs two stands are now available and a third is being erected. In 25 years we furnished propulsion turbine-gear sets for 402 ships totalling more than 2,500,000 hp; turbines only for 23 ships with sore than 1,100,000 hp, and gears for 41 ships with 900,000 hp. This experience combined with the remarkable equipment described herein will enable us to keep right on pro ducing turbine-gear, seta that set new standards for the en tire industry. { j j