The vibrations of integral frame reciprocating compressors are dependent upon many factors including mounting or foundation, operating conditions (speed, load, etc.) maintenance conditions, as well as the basic design of the machinery. However, design deficiencies can take the form of excessive maintenance, wear, or actual fracture of the reciprocating, rotating or stationary parts.
Typical Failures Caused by High Vibration include:
- Broken & bent crankshafts
- Bearing damage & bearing cap stud bolt failures
- Frame & cracked support failures (tie down bolts, skids, etc.)
- Broken crosshead guide & distance piece bolts
- Cylinder scuffing
- Valve failures
- Crosshead guides & distance pieces
In some cases, the failures could be caused by improper installation or lack of maintenance. Others can result from improper application or inadequate design for the operating conditions. However, the majority of these failures could be a result of frame distortion. Frame distortion or dynamic flexing of the frame may be caused by overloading, excessive unbalance, or anchor bolt problems. The foundation is normally considered to be an integral part of the frame in providing the overall strength to resist the large forces transferred from the crankshaft to the bearings and into the frame. Consequently, the foundation design becomes an important factor in attaining long-term reliability.
Potential Causes of Vibrations & Failures in
Reciprocating Engines & Compressors include:
- Overloading
- Excessive unbalance
- Inadequate or lack of cylinder supports
- Large thermal gradients
- Lateral & torsional critical speeds
- Cylinder & piping resonance
- Inadequate foundation mass or stiffness
- Skid & tie down stiffness
- Grout integrity
- Engine frame stiffness
- Bearing load capability
These costly failures could be avoided by improving the frame/foundation system to withstand the forces without damage. Although a reciprocating compressor crankshaft cannot be balanced to the degree that a centrifugal compressor can, the forces should be minimized. Because of changing conditions or product profitability, reciprocating compressors are commonly switched to other services & re-cylindered. As a result, the balance condition is changed & often overlooked.
