CBM-2010 Condition Monitoring Summit Join or Manage Your Profile Posting Boards Maintenance and Reliability Maintenance Connections (tm) Message Board Steam Turbine coupling bolt elongation
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Is there any calculation formula to calculate turbine-generator coupling bolts elongation, considering parameters like PCD of coupling, coupling bolt OD & effective length , coupling bolt material young modulus of elasticity, rpm, power & toque values ???
Can anybody help ??? regards |
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Is there any calculation formula to calculate turbine-generator coupling bolts elongation, considering parameters like PCD of coupling, coupling bolt OD & effective length , coupling bolt material young modulus of elasticity, rpm, power & toque values ??? What torque value to be considered--- torque at full load or starting torque of T-G ? If starting torque then how to calculate it ?? Full load torque can be calculated by Power=torque x rotational speed.
Can anybody help ??? regards |
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First question - what type of coupling?
My thoughts in general: If the coupling was assembled very loosely, then coupling bolts might carry some of the torque load as a shear load. However if coupling is assembled properly, then coupling bolts in tension simply provide a normal force for mating surfaces... friction of the mating surfaces carries the torque. |
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Turbine-Generator coupling is rigid coupling, tightened with 12 nos. coupling bolts. There is diametral clearance of 0.01 to 0.02 mm (maximum) between coupling hole to bolt, so it is rigid one.
regards kamnesh |
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ok, there is clearance in the holes, so the bolt doeos not transmit torque.
I suppose elongation could be computed with knowledge of torque value used, bolt type and grip length. But I don't know what you would do with that info. Are you trying to determine the correct torque for the bolts? If so, the best approach is ask the coupling manufacturer. If that info is not available, you can apply standard charts based on bolt size and bolt material. There is a chart in EASA Technical Manual page 11-47 which applies to "SAE GRADE 5 — METAL-TO-METAL CONTACT ONLY...SOCKET HEAD (HEXAGONAL) - HIGH STRENGTH ALLOY STEEL - COUPLING BOLTS)". I can list a couple of those values if that's what you're after. |
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Pete he probably wants to know the life of bolts. If so much permanent set has been produced, these should be replaced. DPT reveals no flaws. We did not change them even after 30 years service and have no problems / failures.
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I want to know , whether torque calculated by formaula Power=torque x rotational speed, is sufficient to design a coupling bolt of such rigid coupling ??? I personally understand that torque calculated with above formula doesn't hold good as maximum torque transmitted at Turbine-Generator coupling occurs only when machine is put on barring gear , not at full load. I want to know how to calculate max. torque value tramsmitted. So my requirement is what is maximum torque, what is formula to calculate bolt elongation value, with help of maximum torque transmitted.
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In case of turbine(LP to HP) , half of the bolts are clearance bolts carrying the torque and for them the clearance is 10 to 20 microns. Rest of the bolts have greater clearance and simply provide the gripping power.For generator end , LP and generator, all bolts are fitted bolts and no bolt is clearance bolt and hence all these bolts share the torque.I also think that maximum torque will be transmitted when turbine is on barring gear.
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You have several factors. First I would like to make a comment. After 3 pulls get new bolts.
Dry or lubricant - what kind of lubricant. Do a search and you'll find a chart on the www giving torques of dry, oil, grade 8, etc... Cordially, Sam Pickens pdmsampickens@gmail.com |
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Sam could you please quote some standards reference for this? We actually use over and over again these bolts till dye penetrant check comes up with something. |
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Bolt elongation depends upon the bolt stress required to provide sufficient clamp load. "Sufficient" clamp load is that which will preven joint separation and coupling slippage. As mentioned earlier, coupling torque is transmitted through the shear force of the bolts as well as by the friction between the coupling halves. The load is calculated based on the torque transmitted by one rotor to another. Indeed, this is where many of the factors which you had mentioned come into play. It's a complex exercise. However, once you know what clamp load is required, calculating elongation is quite easy to do.
A couple of notes: Conventional "fitted" bolts are not fitted. They may be during installation but, as soon as they're tightened, their diameter reduces and, they become "sloppy bolts". Consequently, slippage can occur. Expanding-sleeve hydraulic coupling bolts have been developed to avoid this problem. "Three pulls and get new bolts"?? Unless you're intending to tighten these bolts awfully close to yeild (or high-temperature creep is an issue) and have no way of measuring this, it doesn't matter how often the bolts are "pulled". Bolts are resilient springs. Bolt "torque" is meaningless. It is simply an indication of how much resistance there is when one tries to turn a nut. One bolt torqued to a certain value may be too loose while another identical bolt tightened to the same torque (with a calibrated torque wrench even!) may be too tight. Hence, the requirement to measure elongation as verification of final bolt load. Measurement by ultrasonic means is the most accurate and convenient method. Best regards, Jörg Hevii Technology |
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Measurement by ultrasonic means is the most accurate and convenient method.
Hevii,you mean we can use the ultrasonic to measure the bolts elongation,but how  |
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There are specialized ultrasonic devices available which measure bolt elongation. These are NOT the same as simple flaw detectors or thickness gauges. They're actually not very expensive. However, they do require significant operator expertise to produce valid results. Here's a link to the equipment which we use:
http://www.heviitech.com/Hevii_UT.html Best regards, Jörg Hevii Technology |
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Dear Yahoo,
I think you'll find by visual inspection the degration and deterioration. Many times I've pulled bolts to find sharpend threads and elongegation. Next you may find G-2 to G-8 without reason. Not only is this practice good on bolt thinking - it is great to keep the threaded hole in better condition. Cordially, Sam Pickens pdmsampickens@gmail.com |
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I have to admit I had never heard a limit for re-using bolts. I looked in a reference and found there are some limits for reusing high strength bolts in some circumstances.
"Guide to Design Criteria for Bolted and Riveted Joints", 2nd Ed, by Kulak, Fisher and Struik states:
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One more comment: never use heavy lubricant or STP. You will never get a safe condition where the bolt will be secure. Something I have done however when assembling something like a flash tower (may have a 108 bolt flange & 1 1/8" bolts); use C5A and light oil. Mix this to a think consistantcy so you can dip the bolt and it'll run off mostly leaving a thin coat.
What has been found if you use STP (research) trying to join metal surfaces - they will not come together. Extremely difficult or impossible to break the film and acheive metal contact. They will loosen during service. So, you all, heavy anti-seize is a no-no in most or some instances. Use extreme care Cordially, Sam Pickens pdmsampickens@gmail.com |
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CBM-2010 Condition Monitoring Summit Join or Manage Your Profile Posting Boards Maintenance and Reliability Maintenance Connections (tm) Message Board Steam Turbine coupling bolt elongation
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