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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Superficial discharges on generator
Registered Member I can not assure the H2 purity was OK in the last years, unfortunately it was not a controlated parameter in this generator. The cable that is seen is a Pt100 cable, this symptom is found in similar areas where the cable is not present. I see corrosion in this area, I expected to be a result of ozone but it can be there first. I assume that radial fields find out a high resistivity path through the core an they produce discharge in the corrosion area but it is very strange!!! I am concerned... [ more ]
Registered Member As you said, pd powder normally shows up in areas of high electric field. This doesn't look like that. Even if that cable were at high voltage, the pd would show up concentrated between the cable and ground... but it doens't look like that... has an appearance as if it was sprayed onto both the cable and the core. Also as you alluded, pd does not occur as readily in hydrogen as it does in air. [ more ]
Registered Member The base metal (compression plate) is magnetic steel. The white powder seems to be a result of corona discharge (but why a high electrical field there?), I think it is not a metalurgical problem/failure. [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Belt driven motors
Registered Member Thanks for all the replies. [ more ]
Registered Member In general the answer is "yes", belt driven motors should have cylindrical rolling element bearings on the drive end (DE). Ball bearings will work and are often found in belt and chain drive applications, but will experience reduced life when compared to direct coupled applications. Please make sure to uniquely identify motors with cylindrical rolling element bearings as these bearings are not well suited for direct coupled application. If used in a direct coupled drive arrangement the... [ more ]
Registered Member I have seen several smaller (less than 10 HP?) motors with deep groove ball brngs on the drive end. I don't think there is any problem with them if the design, as Danny says, is correct. D [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Generator bearing turbine end deep crack/hole
Registered Member I think you're dealing with either electrolytic corrosion (electrical discharge) or inadequate lube film strength (viscosity or volume of oil). The pitting and cracking are either pitting from the electrical discharge or spalling due to fatigue of the babbitt material. You may need to send the bearing to a laboratory to accurately determine the cause of pitting and cracking. May I suggest ATS in Marietta, GA as a resource - www.ATSLAB.com Can you use a magnifying glass and look at the pits... [ more ]
Registered Member Is it the bearing insulated? What is about the upper bearing and the Nº4 bearing? It does not seem to be electrical discharge. Try to measure shaft voltage in this point on line, you can instaled a special brush for that [ more ]
Registered Member Because of the location of the damage I would guess you have a problem with your prelube system. Does your postlube last until the unit rolls to a stop? [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Motor Insulation Resistance
Registered Member Thank for your information.The motor is ok its just that the overload setting was wrongly set such that when you start the motor in delta it was tripping because it was drawing more current than the overload setting. [ more ]
Registered Member IR drop when you perform delta connection shoud occur because you have each of three phase insulations in paralel connection and also the leakage throug the motor TB. It is not a earth fault problem, it seem to be an overcurrent. You should measure the amps during the start. Does it reach rated speed? [ more ]
Registered Member A "Y" connected motor resistance is in series where the resistance adds together, delta is a parallel connection, see this link. http://www.firstelectricmotor.com/images/motcon17.jpg Not sure if you have any motor experience but a motor your size should have a LOW resistance between phases, typically I would anticipate using a Wheat Stone Bridge to measure motor resistance. Values should read like 1.04984 ohms, not Mohms. REVAN is correct, 30Mohm to ground is not a concern. You typically use... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Bad day for a good train crew
Registered Member In the days before cell phones and roller bearings, I was returning from a fishing trip to the Salton Sea in a raging sandstorm. As we passed a train, we saw a flatcar load of lumber blazing away. The head-end crew couldn't see it and the conductor in the caboose couldn't either. We stopped at the nearest Highway Patrol office and reported the problem. It turned out to be a "hot box" generated fire. The '59 Chevy lost all the paint on the front end and the windshield was badly pitted. [ more ]
Registered Member Jon Thanks for that posting. It would be great to upload a photo album of the steam engines in the photo alley forum if you care to share. Thanks again Terry O [ more ]
Registered Member I was sent these pictures by a friend who works for UP when this happened. They had several mishaps in a short period of time as I recall. What is interesting is the automated inspection stations that check for "hot boxes" and "dragging equipment". Being a RR affectionado, I try and photograph steam engines as often as I get a chance. While waiting for UP #844 to pass a photo op along the Arkansas River, I had my radio tuned to the RR frequency so I could hear the report broadcast by the... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Turbine inlet pressure set point
Registered Member Just, Water hammering will not result if steam pressure is increased. In deaerator, pegging steam /bleed steam is provided to keep high temperature to liberate dissolved gases. If deaerator outlet temperature is less, it means lack of proper feed heating in regenerative HX before deaerator/ sub cooling in condenser/lack of bleed steam or pegging steam to deaerator. I do not think lower feed water temperature at inlet to boiler will result in water hammering unless and until there is two... [ more ]
Registered Member It may not be the case here and I doubt if it is but... I had a heating issue in my deaerator one time that gave similar indications down stream. At the boiler it was hammering pretty well when cold water entered the boiler. A temporary fix was to raise the water level in the boiler. It cured hammering but caused 2x the condensate levels down the line. Not sure if this helps you at all but to sum it up 88% of issues result from the beginning of the system. [ more ]
Registered Member If steam inlet to condenser has higher enthalpy, saturation temperature coresponding to the pressure will be higher . Also, the cooling requirements may not be met resulting in higher condenser back pressure. Irshad [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
turbine steam parameter shutdown set up
Registered Member Thank you Jawal for your information. Thanks LUX [ more ]
Registered Member Well i have same concern you do. last time the steam inlet pressure dropped to low and machine kept running for several hours without trip, Steam temp was about the trip setting. machine was running partially loaded but within the running zone. I am sure if we had offset to no running zone, controller to signal to common trip and shutdown machine. [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Alfa Laval Centrifuge
Registered Member Did you change any rotating component like, sludge basket, bowls? If so, unbalance may be introduced. It is a high RPM machine, may require precision balancing. Also, looseness may be anothee reason. The locking ring marks on ring and bowl have to be matched and if threads are worn or damaged, may require replacement to eliminate looseness. Bottom bearing of the spindle may be loose on shaft. Overall, it requires dismantling and finding the cause. Irshad [ more ]
Registered Member Contact Doug Johnson of Alfa Laval, very sharp field service tech located in Greenwood IN 317-889-3037 Office 317-250-2566 Cell doug.johnson@alfalaval.com Hope this helps Dave [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
mech seal problem
Registered Member Even if the gland plate is near the bearing housing, leakage can be detected by opening drain plug in the seal housing. Also, is oil level in bearing increasing as seen in sight glass? If grease lubricated , grease condition can be checked. Irshad [ more ]
Registered Member pumping medium is meg liquid.buffer pot is open to atm [ more ]
Registered Member well thnks akhtar..the level goes down may b an inch per shift.also gland plate collar is almost very close to inboard bearinng [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Condenser Tubes Groove
Registered Member Our UNit 1 & 2 condenser manufacturer is different and the design is different. [ more ]
Registered Member Thanks for all your help guys. We verify that the grooves in our condenser tubes is caused by ammonia-oxygen attack because of the condenser design. Our Unit 1 Condenser's manufacturer and Unit 2 condenser. The Unit 2 condenser tubes is always leaking because of the grooves and because there is tube under the air cooling zone. [ more ]
Registered Member jaca beginner, I assume the sea water intake is in the South China Sea or the Pacific. The debris can be a. loose rubbish such as paper, plastic, wood chips etc. b. marine growth, crustaceans such as barnacles If it is (a), you have to clean/improve the screening and trash removal at the intake. If it is (b), it is a much more difficult problem. Typically, barnacles enter when they are tiny (babies), so they can pass through any screen. They lodge themselves at low velocity points and grow... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
magnetic clutch coil got busted/burn-out
Registered Member Excessive air gap will also cause failure. [ more ]
Registered Member If the coil get burned every time it is operated the most likely cause is over-voltage. As Jonesy stated you probably have wrong coil for the application. [ more ]
Registered Member incorrect power supply voltage? or coil incorrect operating voltage for the power supply? 24V or 110V or other [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
MOTOR WITH INVERTER
Registered Member At 1500HZ, 0.6g value is too small to worry about. Take data in velocity and with higher resolution. 2 harmonics of GMF are visible with no sideband activity and is normal. Irshad [ more ]
Registered Member Can u help me with that??? The first gera mesh frequency is 325 Hz and the motor rotates at 25 Hz... I have no idea about the 1500 Hz peak, neither about the above frequencies... [ more ]
Registered Member I assume there are a series of peaks around 1500hz. You should find about 5-6 peaks @ 1500hz and they should be spaced at 2x line frequency, in your case, 50hz. Without any data to view, this is an assumption. I believe this to be rotor bar passing frequency which is normal is electric motors whether across the line start or vfd driven. Dave [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
High Vibration in Vertical direction and resonance
Registered Member Vertical vibration data are missing. Non synchronous single peaks are generally external to system.I think it is a VFD? Try changing your pump RPM.Since your bump test shows 1.6X as natural frequency, try to can find visible base frame flexibility too. Any soft foot checking? Compare with other similar pumps. Regards Irshad [ more ]
Registered Member Dear Akhtar pl find the spectrum attached . Pl note visibaly line stress doesnt seem thr in the system. [ more ]
Registered Member thanks akhtar ..will revert back with answers [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Enbrige Oil Spill in Michigan
Registered Member [rant]Companies keep pushing what they can get away with further and further until it bites them in the butt. It's the public's wrath that is the new feedback system for risk assessment. If the pipe was in a CEO's backyard, the risk assessment would have had a different set of values.[/rant] [ more ]
Registered Member It shows up more, and more. Budgets are swung in the direction of false cost savings, or share holder review sheets. Cost savings means expense cutting,, this is not lean manufacturing. Even in the companies Ive seen who do lean manufacturing properly the maintenance budget gets slashed and normally the worst part of slash is justifiable. It is all the tiny red check marks that mess things up! It is done this way turns fast into it isnt done, or we did what we could with "and or but" at the... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
BP/Transocean Deepwater BOP Control Systems - A Look at Reliability Issues
Registered Member I sertainly agree with your statement, Wally!!. 'They' see maintenance as a cost, most likely not as an benefit to maintain produktivity!!!!!. think global - act local [ more ]
Registered Member This link was part of the new SMRP SmartBrief newsletter. I just received the introduction copy. As common with most disasters, they cited 20 or more anomalies that occurred in the last two days which may have contributed the disaster. http://online.wsj.com/article/...?mod=dist_smartbrief [ more ]
Registered Member Wow, those are some pictures and one of the better reports I’ve seen. I heard on NPR that there were arguments (fights nearly) to push the e-stop and shut the operation down as tell-tale problem symptoms presented themselves. I also heard that many of the technologies were not fully functionally tested as a system before installed. That makes me think they were just there to pacify the regulatory agencies. I also heard that one of the northern European counties (I forget which one, possibly... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
1XRPM sudden Fluctuation causing turbine to trip
Registered Member when you say sudden jump, is it a spike? does both X and Y probe captured the same behavior.. if only one probe, then you have 1 out of 2 trip voting. if this is the case that you have this trip arrangment and it is a spike, then you may have issue on the vibration probe.. but if it is 2 probes capturing the same behavior, then it is genuine.. is this bearing located at the end of condensing chamber? if so, you may have issue on your grounding brush.. an orbit plot could be useful here.. [ more ]
Registered Member the phase is quite steady during increase of 1X vibration. yes, i would think the same here, unbalance should not cause some unpredictable vibration level. I don't know the exact configuration of the trip system but it will trip the system when the vib level already reach 65microns. [ more ]
Registered Member salam pak, how about the phase itself during the increase in 1X vibration? was it constant or shifted over the increase? unbalance may not be the case here. if you have breaking oil film, you would see more sub synchronous vib instead. i would assume you have 2oo2 trip voting for radial vib that both x and y probes registered high vibration and trip the turbine [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Grid type Wire mesh conveyor.
Registered Member I would have liked to document the conveyor with photos but cameras are not allowed. herewith a very basic layout of the conveyor . The out-end roll above the drive have skirts fitted to guide the chain. These looks like non standard attachments. There are steel vertical plates along the length of the machine but these are non suppose to act as guides as its made out of 6mm plate that "hangs" from the sides above onto the grating (bed) of the conveyor these can be lifted out to gain access... [ more ]
Registered Member avs Is your conveyor similar to the attachment? (only rough)are there guides for the chain to run in from the in end to the out end? Has chain stretch been measured on both sides? excessive chain stretch can lead to jumping a tooth on sprocket and then tracking and other probs escalate. [ more ]
Registered Member Again If you were not present for original start and subsequent damage and repair cycles you really cant tell if it is fixed now. With only a section of bad belting forcing your fault now. Belting stretches and contracts when links are distorted, replace worst section now. it is a simple matter to lace in a new piece and try it out. "example" I seen it before where a new mechanic left a screwdriver in a new installed belt. it performed exactly as it had when he had it in hand, the conveyor... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Repetitive Bearing failure - Horizontal Motor mounted vertically
Registered Member Hello, maybe too late for this but i had a similiar problem with different equipment. new installation. we replaced the motor with a different manufacturer and that solved the problem. our buyers had the inexpensive motor route. [ more ]
Registered Member I doubt that this issue is just about the breaings only. It has to be looked into a wider scope. [ more ]
Registered Member Determining the nature of the failures is essential. Remove the next failed bearing and either send it off for analysis of cut it open and compare it to the free wall chart that SKF or FAG or just about any bearing manufacturer will give you. Collect and analyze vibration data to predict the failures while you determine the cause and corrective measures. Premature bearing failures are usually caused by improper loading due to design or installation defects or lubrication problems. The cause... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
pipe strain measurement
Registered Member Hi AKHTAR, For some machines we didnot always get this pipe stain through shaft movement measurement . Example as I knew ,For integrally geared centrifugal compressor and steam turbine we did before we basically check this pipe strain through casing movement measurement. So I think maybe we should use a most sensitive method to do this. Thanks Lux [ more ]
Registered Member It is a word 2007 file and will not open with previous versions of microsoft word. Regards Irshad [ more ]
Registered Member Dear AKHTAR, Thanks for your help. Would you like to re-post your attachments again? the current attachment type cannot be opened . Thanks Lux [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
motor bearing arrangement
Registered Member Hi EP, It is a 4.6 KW Grundfos pump as our 2,100kg/hour steam boiler BFW main pump. As you said a rigid coupling is used between motor and pump and no thrust bearing on the pump. Below is pump information. TYPE: CRNE1-23 XE-P-GI-E-HQQE MODE: A96571769P10507 F 50HZ P2 4.6KW N 4800min-1 Hmax 366.8m Q 3.5M3/H H 231.4m Pmax/tmax 50/120 cw Serial no: 0002 made in DK Thanks Lux [ more ]
Registered Member Top bearing on vertical pump can also support pump weight and pump thrust in cases where the pump has no thrust bearing (rigid coupling is required). 6306 and 7306 are tiny bearings (30 mm shaft). I have a hard time reconciling that with a multistage boiler feedpump application. Out of curiosity, how many horsepower is the motor? [ more ]
Registered Member Dear Joney, Thanks for your reply. From your reply I feel I got some. Thanks. BTW,I will find out this schematic. Thanks Lux [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
new bearing failure
Registered Member If so, wouldn't you expect high potassium levels as well? [ more ]
Registered Member This place is a solution mine for Potash, its possible the pump packing could have allowed solution into the casing somehow. [ more ]
Registered Member The reason for high calcium eludes me. There's no corresponding elevation of Silicon levels, which would suggest dirt got in. Perhaps the new bearing was coated with preservative? If so, I don't believe this is a worry. It may be that this particular electic motor wan't properly grounded before it was put into service. I still think you should investigate the possibility of electrical damage on the surfaces. Unfortunately, the only good way to positively determine electrical damage at such... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
protection for dc motor
Registered Member Found this at:http://www.railway-technical.com/tract-01.shtml Motor Control and Protection As we have seen, DC motors are controlled by a "notching relay" set into the power circuit. But there are other relays provided for motor protection. Sharp spikes of current will quickly damage a DC motor so protective equipment is provided in the form of an "overload relay", which detects excessive current in the circuit and, when it occurs, switches off the power to avoid damage to the motors. Power... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Westinghouse Electric Motor Issues
Registered Member This is a picture of the thrust "buttons". The rotor is coupled to the gearbox with a coupling that allows for 3/16" of axial movement. There is 1 button on the rotor and 1 button on the gearbox that face each other. The idea is, if the motor starts to move towards the gearbox, these buttons will make contact and prevent the motor from running into the bearing shoulders. This picture is of the gearbox's button. The buttons were so "eaten" up that the bearings were trashed as well. As far as... [ more ]
Registered Member I might say that terminal lug is loose? That is easy to check and you probbably already have. I had an 1200 hp unit that stole wrenches and screwdrivers from operators pouch. removed it and there was similar looking arc welding to feet on one side. Motor shop who rebuilt it 4 mos prior said they found nothing but we never had probblem again after they re-installed. That is a welded reciever foot correct? [ more ]
Registered Member I think this is a photo of portion of a limited end-float coupling, correct? What type of coupling and what was condition of the rest of the coupling? Was the machine aligned so the motor sits near magnetic center based on uncoupled run? (Actually I don't think magnetic centering is usually that important, but still seems like data to fill in the picture). Was it aligned to prevent contact of the motor endplay limits (bearing to shaft collar)? What is the driven equipment? Was there... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Spherical Roller Thrusr Bearing -- DAMAGE
Registered Member Riyaz, when you say rise without problem, i would presume the vib reading and oil property are maintaining normal between before and after the rise. hence, i will join this shooting gala. is there any external cooling employed here on the bearing housing? if yes, do check the inspection ball inside the cw return line sight glass to verify the flow is there. casing temperature of 115 deg is very high. actual brg temp must be much higher. what is your ambient temp there? [ more ]
Registered Member Mechanical seal running dry, heat transfer down the shaft to the bearing. roughriderbeach knows nothing, he drinks too much beer when he is home. [ more ]
Registered Member RA Dave, Need to know more about the pump style/manufacture. Sounds like you had proper lubrication, if so the root cause was most probably excessive thrust. This can be caused by deadheading the pump, the thermal growth on the pump shaft could overload the film strength of the lubricant, too low of discharge head can also cause upthrust on turbine pumps. (assuming you were talking about centrifugal pump). [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Humming sound of steam turbine
Registered Member You have some good sugestions. I have a couple maybe not so probable ones. Have you done anything that would change the thrust on the turbine? Load changes or coupling adjustments? [ more ]
Registered Member Nauman, The humming sound is coming from outboard side i.e. steam end? If no vibration problem and spectrum at out board bearing normal, look for the turbine warm up vent. Is it a passing valve? There may be a reason due to an accoustic resonance excited by another machine transmitted through floor or beam. Look out for that. Waiting for your feedback [ more ]
Registered Member Nauman, you posted this a week ago and at what stage are you and your investigation team now when you say it is flow related? other than speed hunting (steady gradual hunts), was there any other hypothesizes related to outboard side you have covered and ruled out? now, i would expect you have increased or decreased the speed to understand the humming sounds more. have you done it? if yes, how was the result like? [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
STG damage - unplanned outage
Registered Member Looks like an overspeed problem to me. The coupling failure was just one of the symptoms. The generator would trip off line on over current and the turbine speed control couldn't/didn't react in time to save the generator, coupling, gearbox, etc. [ more ]
Registered Member I still wonder why if coupling failed did the Bolts not shear? That is secondary purpose of the coupling. Looks like it came out in one piece so perhaps bearing failure that ejected it as assembly. [ more ]
Registered Member A second thought - may be a coupling failure! This could be a generator with single bearing at the out board. Coupling failure starts and there would be a contact between the rotor and stator leading to fire and then what not. [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
what will happen if modify the bearing arrangment
Registered Member MBENSAMA, WILL YOU PL. EXPLAIN WHY IN DF CASE BEARINGS WILL BE LUBRICATED AND IN DB CASE LUBRICATION STARVATION WILL BE THERE. I T5HINK, IN BOTH CASES OIL WILL ENTER THE CLEARANCE BETWEEN OIL WILL ENTER THE BEARINGS. CAN YOU REFER ME TO SOME TECHNICAL DOCUMENT IN YOUR SUPPORT. I WILL BE HAPPY TO KNOW THIS. REGARDS IRSHAD [ more ]
Registered Member Dear Mbensema Thanks you for your idea and suggestion share. In these days I read some information about angular contact bearing arrangement. Also I saw some just as what you said. This is a most possilbe cause by inadequate lubrication because I am told that there is some shallow pitting existing on the damaged bearing yesterday. Thanks LUX [ more ]
Registered Member Are these grease or oil lubricated? It appears to be oil with the slinger ring on the lower shaft. If oil lubricated, the DF orientation can help pump oil towards the inside enabling sufficient lubrication of both bearings. The DB orientation can cause the oil to sling outwards and starve the inner bearing. Your description of the latest failure sounds like it could be lubricant starvation of the inner bearing. Lubrication failures typically will have shallow pittings on the bearings that... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
UNBALANCE LOADING
Registered Member - What's the vector group and type of the transformer? What about no load volatge in magnitudes and phases - What's grounding scheme? (TN-S or any other else?) - Cable arrangement can lead to imbalance inductance to the system which might cause currence unbalance. [ more ]
Registered Member In motors, an unbalance in the supply voltage is expected to create an unbalance in the current which is approx 5-10x as large. (the negative sequence impedance presented by the motor is approx 1/5 -1/10 of the postiive sequence impedance). Unbalance is typically defined as (max deviation from average) divided by average. For voltage, you have an an average of 418.3, a max deviation from average of 422-418.1=3.67 and an unbalance of 3.67/418.3 = 4.35% For current, you have an an average of... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Roughing Pinion Stand Gears Defect-Hot Rolling Mill
Registered Member Thank you so much Dave your explanation very useful [ more ]
Registered Member Those pinions were meant to withstand the shodk of plate going through the rolls. However, you can overload them to some degree by running thicker material in the same amount of runs than the system was designed for. Having said that, I find more evidence of wear (consistant decline of tooth thickness) from the overload in the gearbox driving those pinions. If there is no gearbox, then overload could be some of the cause, but those pinions were designed to withstand a harsh life, and from my... [ more ]
Registered Member Thank you so much Dave and Samuel, Further corrosion, contamination defects. is it maybe another cause wear on gears such as shock or overloading? [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Torque exerted on rotating shafts.
Registered Member Man, I'm not sure how to measure the torque you describe, but it is usually enough to break the shaft on pumps with a large enclosed impeller or on muti-impeller pumps. And they don't have to be back spinning all that fast. The electric motor will stop the rotation instantly and the rotating mass will snap the shaft at the first inboard bearing of the pump. [ more ]
Registered Member To summarize: I think the max shaft torque seen when starting a reverse-rotating pump would be about the same as seen during a normal start (just lasts for a little longer time). My reasoning is above - let me know if questions about it. [ more ]
Registered Member Re: Torque exerted on rotating shafts. [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Fin Fan Motor bearing problem
Registered Member fianda100185, Some electric motors are manufactured to be mounted horizontally, on most fin fans they are mounted vertically. You will need to check with the builder to make sure the motors have the proper thrust bearings for your application. [ more ]
Registered Member Assuming that your fin fans are belt driven as everyone that I've encountered is... What type of bearing failure is being experienced? Ie., inner, outter, ball, cage? Which bearings are failing; outboard, inboard or both? Is it possible that the belts are being over tightened upon installation? Is it the same tradesperson changing belts? Is the machine alignment between sheaves, etc correct? [ more ]
Registered Member what is a fin fan motor? what is the application? In what way are the bearings failing, is it always rhe same failure mode? what type of bearing? Always the drive or non drive end bearing? do you have any photos of the failed bearings? any other details, motor rpm etc [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
RCA Training
Registered Member Latent Cause Analysis by The Failsafe Network is also an excellent class. http://www.failsafe-network.com/ [ more ]
Registered Member Sachs Salvaterra & Associates put on a very good course. (315)487-4390 [ more ]
Registered Member TapRooT® Training is provided around the world. For course locations/dates, see: http://www.taproot.com/courses.php For more information about TapRooT® and success stories from users, see: http://www.taproot.com/about.php And for a paper about how TapRooT® works, see the Root Cause Analysis Blog and click on the first article in the "Popular Posts" section (top-right). See the Root Cause Analysis Blog at: http://www.taproot.com/wordpress/ Thanks Mark [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Motor failure
Registered Member Hi all, At present, We got the analysis report of motor damaged bearing from Bearing vendor SKF .Due to chinese version I willnot post the document. In the report the primary reasons are as follow for your reference. 1. The damage of the bearing was due to excessive uni-directional force from shaft acting on bearing. 2. The excessive pre-load created uneven rubbing and accelerated frictional wear, as observed on the damaged bearing. 3. The excessive pre-load was a result of the overly tight... [ more ]
Registered Member Pete, Thanks for your help . Happy new year! Regards lux [ more ]
Registered Member Glad I could help. The EASA procedure for checking allowance for expansion is posted on their site: http://www.easa.com/mo/TN-pdfs/TN42-1005.pdf [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
new mechanical seal check
Registered Member Mechanical seals , when stationary will normally not hold gas. It will leak, depending upon what type of seal you have, what is the preloading, it is dry or gas seal? Check for seal face flatness under monochromatic light source . For gas, it should not be more than 2 light bands. Regards Irwshad [ more ]
Registered Member Hello, Jawal, I ever had worked at chemical plant for 8 years, Met many mechanical seal issues . But I know that after rebuilding mechanical seal commonly we use water booster pump to pressure mechanical to check seal under static status for any leakage. I remember if doing seal test with gas a little of mechanical seal can be kept from leakage. Thanks Lux [ more ]
Registered Member for the limit, we can run up to 5 psig of leakage with drain line to atmosphare wild open. its single mechanical seal. [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
vertical pumps
Registered Member Never use a concentric reducer on pump suction. [ more ]
Registered Member One more important thing: Is concentric pipe reducer used on the pump suction close to pump suction nozzle / flange. If eccentric reducer pipe is used the sloping side should be at the bottom and the straight one should be at the top. When the sloping side is at the top, there are formation of air bubbles leading to cavitation. [ more ]
Registered Member If it has cavitation, check vibration. High frequency energy mounds will be there in the spectrum. Second thing, check that the pump has no obstruction in flow path. Third thing, the pump is not very close to the wall of the sump as compared to the first pump. Fourth thing, if there is a bell mouth or cruciform, check whether these are installed correctly and not damaged. Check the height of the bellmouth from floor. If it is less than as mentioned in OEM MI, there may be cavitation. If the... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Root cause of a broken gear shaft
Registered Member Kevin Ku, Whats the current status of these gearboxes? Has there any other shaft failure occured during the last 15 months? Regards, Mohammad [ more ]
Registered Member This cut looks like a cup,it may be due to stress concentration from the inner race fit with the shaft regards mahmood el.nagar nubaria power station Egypt [ more ]
Registered Member Has there been any machine work done to the bearing fit on this shaft? [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
what is feature about "False Brinelling" ,why the bearing failed
Registered Member Only select equipment. The practice was initiated after root-cause analysis indicated false brinelling. This lead to vibration analysis of the standby pump, showing that it indeed was being excessively vibrated by the pump next to it. I know that we then used vibration analysis to check the standby pumps that were critical service or had a history of similar failure to find other examples of high standby vibration. I think that is the right approach. The rotation, especially in a nuclear... [ more ]
Registered Member Rich, do you rotate all rotating equipment in standby mode or only for selecte equipment? [ more ]
Registered Member In addition to the advice about grease, periodic rotation of the stationary shaft will minimize the effects of the false brinnelling. We used to do this with a weekly operator task to rotate the shaft of a standby high pressure pump that had experienced false brinnelling failures, and we had confirmed high vibration levels during shutdown, due to the adjacent pump. Since yours is a crushing application, you are probably talking about high levels from the adjacent machine. In some cases,... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
GT fram 5001 #2 Brg high vibration during startup
Registered Member You did not tell when this problem appeared? After a cold startup, due to rapid starting. "\ Or startup after a shutdown and thermal bow etc? What has changed ? Some balance weight got disloged? [ more ]
Registered Member Dear Mohzek, I am not sure whether your problem has been solved by now. Vibration troubleshooting is always troublesome. As per your description, it appears that, you might have vibration due to unbalance. This could be caused due, load coupling alignment problem and GT base plate loosens. To give you more information, you should give us some more detailed data such as HP speed, bearing drain temperatures. The older FR5001 have also one seismic probe on the GT axial compressor casing. The... [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Electrical fluting bearing defect
Registered Member Grounding brushes are ineffective on motors driven by modern VFD's. What is needed is proper cable installation and high frequency grounding. Insulated bearings help as well. [ more ]
Registered Member NEMA and EASA both recommend an insulated bearing/housing on both motor bearings and one shaft grounding brush when running on a VFD. It appears the motor is quite old? Most common "source" of the electrical fluting is dis-symmetry in the rotor, stator or air gap between the two. Older motors were not designed to run on VFD's, the insulation system, cooling ability, rotor design are just a few examples that old motors do not have... [ more ]
Registered Member Looking at the picture of the grounding brush, I see a lot of build-up on it. I have seen times where dust, grease, debris, etc build up on the interface at the shaft will act as an insulator. This in effect eliminates the path of least resistance through the brush and puts it back through the bearings. The brushes must be kept clean to work correctly. Gary B [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
UNbalance on Heat Treat Furnace extraction Fan
Registered Member Thanks Dave i will try this [ more ]
Registered Member Get close first while fan is cold. It takes about 15-20 min for our oven to heat up, once up to temp take your new reference run. Shutdown and let cool to a tolerable level, add trial weight, heat back up repeat normal balance procedure, just make sure oven is up to temp before storing data... [ more ]
Registered Member How do you balance them hot, and thanks for the input [ more ]
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Reliability Engineering for MaintenancePosts about Root Cause Analysis
Gear Box Shaft broken
Registered Member I agree. Looks like this occurred over some time, as there is some hardening near the top of the last photo. Probable crack propagation over time. Would need more detailed photomicrographs to be sure. Might also want to check on installation procedures, in case damage occurred in the keyway area during installation. [ more ]
Registered Member Excessive torque (static and/or dynamic) will cause fracture in a cone shape. A stress concentration at the shaft keyway was the probable starting point. Torque measurements are highly recommended, since this looks like a large and expensive machine. Walt [ more ]
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