COMPRESSOR SURGE

[173894]

WHAT KIND OF DAMAGE TO THE BEARINGS, IMPELLORS AND DIFFUSORS CAN ONE EXPECT WHEN A MULTI STAGE TURBO COMPRESSOR RUNS INTO SURGE CONDITIONS FOR PROLONGED PERIODS OF TIME.

 

[Franko]

Excessive surging must be avoided. It can cause fatigue of components, including covered impellers, as well as piping. Open impellers and axial compressors can withstand much less surging. Thrust bearings have dynamic loading due to pressure reversals, with large swings especially in inlet pressure. During reverse flow the unit acts as an inefficient turbine - with speed increase for turbine drives. Torsional natural frequencies are excited but typically surge frequency is much lower. Rotor/bearing natural frequencies are also excited so there can be radial bearing damage, especially if there is one-cell rotating stall before surge that can cause high rotor excitation. Vaned diffusers can also be excited, and increase dynamic loads at vane passing frequency on the near-by impellers. Continuous surging will increase internal temperatures giving alternating thermal stresses, including that during rapid recovery.

 

[hacksaw]

It can wreck everything, rotor, cases, bearings,thrust bearings you name it.

 

[Franko]

CAN is a big word - depends on how rugged the unit is. Customer failed tens of covered, welded impellers in four identical 30,000 hp 4-stage centrifugals. Continuous surging likely helped propagate the cracks; but it was finally proven with strain-gages, read with a slip-ring, that liquid ingestion initiated them. However there were no other failures. See:

http://tamu.edu/publications/turbo31/t31chapter6.pdf

that describes another unit with a piping failure and shows data for the case that had liquid ingestion