New Product Info
Optimized Bearings Provide Long-Term Vibration Solutions(Jul 20,2017)
Over a 13-year span, a major South American oil company’s maintenance department fought recurring high vibrations in three gas reinjection compressor trains. To reduce the likelihood of machine trips, technicians field balanced each compressor once or twice a year and replaced the worn tilt pad journal (TPJ) bearings and O-ring dampers yearly. The downtime from implementing these preventative measures and from trips in the compressor trains resulted in 1% capacity loss each year and additional flaring of the gas.
A thorough analysis of the compressors and inspection of damaged components pointed to a two-part solution: Flexure Pivot journal bearings and an integral squeeze film damper (ISFD technology).
In 2013, the compressors were placed back in service with the optimized bearings (Figure 1).
Since then, the compressors have exhibited low vibration levels that do not grow over time. They have had no trips and have not required field balancing for continuous operation. Overall efficiency has increased by approximately 1% and site profits have improved.
Finding the root cause
Put into operation in 2000, each compressor train has two casings: a low-pressure casing and a high-pressure casing. The vibration issues occurred in the first low-pressure casing only.
The original equipment manufacturer (OEM) bearings were five-pad, load-on-pad, point-contact-pivot TPJ bearings, with a bearing outer diameter smaller than the machine casing bore to provide a squeeze film damper function. O-rings at both ends of the bearings were installed to provide stiffness.
Each direct OEM bearing replacement would reduce rotor vibrations for a time. As months wore on, however, vibrations would increase again, requiring repeat maintenance and bearing replacement.
Inspection of the removed OEM bearings showed severe pivot wear on the tilt pad and bearing shell bore (Figure 2). This wear increased the bearing clearance by 63 microns or more in a five-month period, which resulted in increasing vibrations. The inability of the O-rings to provide centering capability under static deflection, together with the increased
vibration, resulted in bearings bottoming out (Figure 3) and loss of squeeze film damper performance. These factors converged to increase vibrations over time in the compressors.
Solving the challenge
With two root causes for the recurring vibrations — pivot wear and unreliable squeeze film damper performance — a combination of two solutions was implemented.
To address the pivot wear, a Flexure Pivot tilt pad journal bearing was used. The Flexure Pivot design has a pad and pivot that is integral to the bearing shell, eliminating metal-to-metal contact between the pad and shell when the pad tilts (Figure 4). The method of manufacturing the bearing, via electrical discharge machining (EDM), provides tight control of the clearance and preload for bearing optimization. With the elimination of pivot wear, the Flexure Pivot bearing maintains the original bearing clearance and original preload (changes in which can contribute to vibrations).
Over a 13-year span, a major South American oil company’s maintenance department fought recurring high vibrations in three gas reinjection compressor trains. To reduce the likelihood of machine trips, technicians field balanced each compressor once or twice a year and replaced the worn tilt pad journal (TPJ) bearings and O-ring dampers yearly. The downtime from implementing these preventative measures and from trips in the compressor trains resulted in 1% capacity loss each year and additional flaring of the gas.
A thorough analysis of the compressors and inspection of damaged components pointed to a two-part solution: Flexure Pivot journal bearings and an integral squeeze film damper (ISFD technology).
In 2013, the compressors were placed back in service with the optimized bearings (Figure 1).
Since then, the compressors have exhibited low vibration levels that do not grow over time. They have had no trips and have not required field balancing for continuous operation. Overall efficiency has increased by approximately 1% and site profits have improved.
Finding the root cause
Put into operation in 2000, each compressor train has two casings: a low-pressure casing and a high-pressure casing. The vibration issues occurred in the first low-pressure casing only.
The original equipment manufacturer (OEM) bearings were five-pad, load-on-pad, point-contact-pivot TPJ bearings, with a bearing outer diameter smaller than the machine casing bore to provide a squeeze film damper function. O-rings at both ends of the bearings were installed to provide stiffness.
Each direct OEM bearing replacement would reduce rotor vibrations for a time. As months wore on, however, vibrations would increase again, requiring repeat maintenance and bearing replacement.
Inspection of the removed OEM bearings showed severe pivot wear on the tilt pad and bearing shell bore (Figure 2). This wear increased the bearing clearance by 63 microns or more in a five-month period, which resulted in increasing vibrations. The inability of the O-rings to provide centering capability under static deflection, together with the increased
vibration, resulted in bearings bottoming out (Figure 3) and loss of squeeze film damper performance. These factors converged to increase vibrations over time in the compressors.
Solving the challenge
With two root causes for the recurring vibrations — pivot wear and unreliable squeeze film damper performance — a combination of two solutions was implemented.
To address the pivot wear, a Flexure Pivot tilt pad journal bearing was used. The Flexure Pivot design has a pad and pivot that is integral to the bearing shell, eliminating metal-to-metal contact between the pad and shell when the pad tilts (Figure 4). The method of manufacturing the bearing, via electrical discharge machining (EDM), provides tight control of the clearance and preload for bearing optimization. With the elimination of pivot wear, the Flexure Pivot bearing maintains the original bearing clearance and original preload (changes in which can contribute to vibrations).
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