Overspeed tests

The overspeed test is a form of proof test, in that it looks for a failure. In this case, it is a permanent deformation. Not all permanent deformations are failures. In fact, manufacturers have autofrettaged high tip speed impellers for decades. The fourth edition of API 617 was somewhat misleading as it identified the bore as the only critical area. On... 

Objectives, Hydrostatic Test. Impeller Overspeed Test. 

This inspection will be performed on the flywheel after final machining and the overspeed test. 

The design speed of the flywheel is 125 percent of normal speed. An overspeed test of each flywheel at the design speed is performed prior to assembly. Refer to pump flywheel integrity Section 5.4.1.1. 

The rotor speed must then be inereased to trip speed to eheek the overspeed trip setting, then redueed to maximum eontinuous speed and held for a minimum of 1 hr. Extended testing time should be alloeated if neeessary to reaeh satisfaetory equilibrium eonditions. Tlie lube oil must be held near design inlet temperamre during tlie meehanieal test. Data logging should be done in 15 min intervals for all measuring points. 

Overspeed is the speed at which the expander rotor is tested to prove its design capability for this service. Overspeed is 115% of maximum continuous speed. 

The tests are performed in a special overspeed chamber, which is evacuated to a minimum level to minimize windage pumping of the impeller and to control the temperature rise in the impeller. 

Mechanical testing of the non-lubricated helical-lobe compressors is modified from the previously described lest. For example, API 619 only requires a two-hour mechanical run. The procedures and monitoring requirements are generally the same as previously described. A run comparable to the overspeed run is the heat run. The compressor is run on air at the maximum allowable speed, and the discharge temperature is allowed to stabilize at a value 20°F higher than the rated discharge temperature. The compressor is then run for 30 minutes. 

E.4.4 It may be useful to verify the overspeed trip setting for the HPRT at the manufactnrer s test facility. Determining the runaway speed during a water test may be considered, but this speed can be accurately calculated once performance with water is known. Rnnaway speed for gas rich-steams cannot be determined by water tests. 

ISO3046/IV Reciprocating internal combustion engines Performance. Part 1 Specifications for standard reference conditions and declarations of power, fuel consumption and lubricating oil consumption. Part 2 Test methods Part 3 Specification of test measurements. Part 4 Speed governing. Part 5 Torsional vibrations. Part 6 Specifications for overspeed protection. Part 7 Specifications for codes for engine power. 

If the bond between the copper tube and the A286 support tube is neglected, the centrifugal pressure of the copper on the overwrap is 2.52 MPa (366 psi) at 12,000 rpm, which produces a hoop stress of 298 MPa (43,200 psi) in the composite overwrap. The hoop stress in the overwrap itself, due to the 12,000-rpm rotation, is 150 MPa (21,700 psi). Hence, the combined hoop stress in the overwrap is 447 MPa (64,900 psi) at design speed and 541 MPa (78,500 psi) at the overspeed (13,200 rpm) condition. The observed tensile strength in the hoop direction for the composite at 77 K was —896 MPa (130,000 psi). Hence, sufficient structural protection under rotation should be provided by the overwrap. Warm tests on the complete generator were recently conducted up to 12,000 rpm with no apparent problems with the shield construction. 

TS-SRCF1.1-1 Material hoisting overspeed limit All Material, Combined Test room... 

A routine shutdown of a piece of equipment offers an excellent opportunity to test alarms and trips. For example, if a turbine is to be shut down for maintenance, its speed can be carefully brought up to see if the overspeed trip is operative. It is no exaggeration to state that if an overspeed trip is inoperative, the turbine should not be run. 

Turbine over speed could result in a maj or turbine feilure that produces missiles these would pose an internal hazards threat (see APIOOO Internal Hazards Topic Report, Reference 6.3). The turbine stop valves and the reheat stop valves are all closed by actuation of the overspeed trip system, which is completely independent of the turbine control system (Sections 10.2.2.4.3 and 10.2.2.5.1 of Reference 6.1). The probability of destructive overspeed condition and missile generation, assuming the recommended inspection and test frequencies, is less than 1x10 per year. In addition, the orientation of the turbine-generator is such that a high-energy missile would be directed away from the nuclear island (Section 10.2.2 of Reference 6.1). 

The rotor is balanced when the rotor winding, insulation, and retaining rings are in place. It is then heated to a high temperature and test-run at overspeed. This restdts in the winding adopting its final form before the rotor is finally balanced to satisfy the relevant requirements. The normal overspeed is 120 percent of the rated speed. Certain of the balancing planes remain accessible when the rotor is installed in the stator. 

A back-to-back test bed has been installed for research purposes. The gears transmit a power of30,000 kW at 6380/15,574 rpm nominal speed, with the capacity of 120 percent overspeed. 

Steam turbines are equipped with an emergency overspeed protection system that is separate from the main governing system. In the event of excessive rotor speed, this system shuts down the steam flow to the steam turbine by closing both the stop and control valves. This is an electronic failure detection system that is redundant and can be tested during operation. 

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