Baker Hughes, a GE Company (BHGE), Machinery Diagnostics Services from it's Bently Nevada product line helped an European oil and gas customer to significantly reduce downtime and production losses by performing a field balancing instead of time and cost intensive sending the unit for repair to replace the rotor.
Vibrations at Alarm Levels
Just 300 hours after returning from the 15,000 hours inspection, vibrations of a LM2500+ gas turbine unit of an oil & gas site reached alarm levels under certain load conditions. Since down-time was critical due to high demand and maintenance activities on other units, it was decided to field balance the rotor. After the units cold and hot conditions were compared to verify the repeatability of vibration, it was confirmed that this was a balancing issue and no other possible malfunction.
Data & Analysis
According to Modal analysis 1st GG HP flexible mode is at 6749rpm and 6719rpm in vertical and horizontal direction, 2nd GG HP mode is at 9847rpm and 9803rpm, and 1st HPT rigid mode is at 4493rpm and 4619rpm. At 8600rpm (between 1st and 2nd flexible mode), 1X of CRF was: 28,6 mm/s pk @ 26°. Based on polar plot of the CRF sensor and previous knowledge of the unit, GE’s Bently Nevada Machinery Diagnostic Service Engineers decided to mount a horse shoe with 2 bolts and 2 nuts for a total weight of 113g at 144° as counterbalance. To completely cancel the unbalance response, the ideal final weight would have been at the same spot but twice heavier, which was not suitable. After the first balancing run, the vibrations were reduced to half the amplitude levels and even below other units levels. The customer was very satisfied with this fast on-site balancing results after mimized down-time and decided to put the unit back to operation.
Value to customer
Significantly reduced downtime, due to GE knowledge and reduced balancing procedure in the field
GE Power saved up to a million € by doing a field balancing instead of sending the unit back to repair, replacing the rotor and saving on production losses