API 612 2003 pdf free download

API 612 2003 pdf free download.Petroleum, Petrochemical and Natural Gas Industries—Steam Turbines—Special-purpose Applications.
9.3.2 The vendor shall correct the model if it fails to meet either of the criteria contained in a) and b) below. a) The actual critical speeds determined on test shall not deviate from the corresponding critical speeds predicted by analysis by more than 5%. Where the analysis predicts more than one critical speed in a particular mode (due, for example, to the bearing characteristics being significantly different horizontally and vertically or between the two ends of the machine), the test value shall not be lower than 5% below the lowest predicted value nor higher than 5% above the highest predicted value. It is possible, particularly on electric motors, that the vertical and horizontal stiffnesses are significantly different and the analysis predicts two differing critical speeds. Should the operating speed fall between these critical speeds, these two critical speeds should be treated separately, as if they resulted from separate modes. b) The actual major axis amplitude of peak responses from test, including those critically damped, shall not exceed the predicted values. The predicted peak response amplitude range shall be determined from the computer model based on the four radial probe locations. 9.3.3 If the support stiffness is less than two times the bearing oil film stiffness, the absolute vibration of the bearing housing shall be measured and vectorially added to the relative shaft vibration, in both the balanced (9.3.1.a) and in the unbalanced (9.3.1.d) condition, before proceeding with the step specified in 9.3.1.e. In such a case, the measured response shall be compared with the predicted absolute shaft movement. 9.3.4 Unless otherwise specified, the verification test of the rotor unbalance shall be performed only on the first rotor tested, if multiple identical rotors are purchased. 9.4.2 Unbalance masses shall be placed as described in 9.2.6; this may require disassembly of the machine. Unbalance magnitudes shall be achieved by adjusting the indicated unbalance that exists in the rotor from the initial run to raise the displacement of the rotor at the probe locations to the vibration limit defined by 9.2.10, Equation 5 at the maximum continuous speed; however, the unbalance used shall be no less than two or greater than eight times the unbalance limit specified in 9.2.6, Equation 1. The measurements from this test, taken in accordance with 9.3.1.a and 9.3.1.b shall meet the following criteria: a) at no speed outside the operating speed range, including the separation margins, shall the shaft deflections exceed 90% of the minimum design running clearances; b) at no speed within the operating speed range, including the separation margins, shall the shaft deflections exceed 55% of the minimum design running clearances or 150% of the allowable vibration limit at the probes (see 9.2.10). 9.4.3 The internal deflection limits specified in 9.4.2.a and 9.4.2.b shall be based on the calculated displacement ratios between the probe locations and the areas of concern identified in 9.2.11, based on a corrected model if required. Actual internal displacements for these tests shall be calculated by multiplying these ratios by the peak readings from the probes.
9.5 Torsional analysis ? 9.5.1 For units including gears or generators, or for units comprising three or more coupled machines, or if specified, the vendor having unit responsibility shall ensure that a torsional vibration analysis of the complete coupled train is performed and shall be responsible for directing any modifications necessary to meet the requirements of 9.5.2 through 9.5.6. 9.5.2 Excitation of torsional natural frequencies may come from many sources which may or may not be a function of running speed and should be considered in the analysis. These sources shall include, but are not limited to, the following: a) gear phenomena such as unbalance, pitchline runout, and cumulative pitch error; b) cyclic process impulses; c) torsional transients such as start-up of synchronous electric motors and generator phase-to-phase or phase-to- ground faults; d) torsional excitation resulting from electric motors and rotary type positive displacement machines; e) control loop resonances from hydraulic, electronic governors, and variable frequency drives;