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API-610 requirement for combined mechanical and electrical run out


I am doing the inspection of mechanical and electrical run out on a SA479-316 shaft for a centrifugal pump. API-610 indicates combined electrical and mechanical run out to be less than 0.005 mil. Run out is done with dial indicator for mechanical and a proximity probe for the electrical simultaneously. Mechanical run out is recorded as .0025 and electrical run out is 0.0035 mil. Does the radial probe measurement of .0035 meet API-610 since probe is picking up both mechanical and electrical conditions or do the 2 need added to get the combined reading as indicated in API-610? I have condition where probe reads .00015 and mechanical is .005. This seems a bit strange. Also why is there magnetic permeability in this A479-316 shaft. Is it due to machining and polishing. It was degaussed.

Jeff McHone
Inspection - Phoenix, Arizona

August 1, 2009

You do not add the reading from the dial indicator to the reading of the electrical probe. The API limit is applied to the electrical reading by itself. The reading from the electrical probe includes the mechanical run-out. The purpose of the API spec is to prepare the probe area of the shaft for on-line monitoring equipment after final installation. That equipment uses the same type of electrical probe to monitor machine condition. If the electrical run-out is below a certain limit, then the readings on the monitoring equipment can be easily interpreted as the shaft vibration or the shaft orbit within the sleeve bearing. If the electrical run-out is not below limits, than the readings on the monitor would indicate false levels of shaft vibration or orbit.

Antonio Savarese
- Arlington Texas

September 17, 2011

The probe reads the combined mechanical and electrical run-out. if the combined run-out is more than a certain value, it has to be subtracted from the vibration readings , to arrive at the actual vibration value during operation.

While checking electrical run-out, the shaft should be turned slowly at about 100 rpm, to get correct value.

Surendra Bhuvanagiri
Rotating equipment - Doha, Qatar

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