expander - compressor failure 1

[arbainmahmood]

Hello, anybody out there has any experience in expander - compressor failure?
Ours is Rotoflow, 4 stage expander - compressor configuration, H2 service in ethylene plant. In July 2008 we experienced a catastrophic failure in Unit-A, both expander & compressor wheel broken into pieces. Normal speed 44,000 rpm for unit A~C & D is 28,000-30,000 rpm. Pressure drop across unit A ~ D normally from 30 barg to 4 barg, temp from -90 deg C to - 160 eg C. It failed during routine start up & during manual loading of unit C just after unit D was in auto mode. Unit A went overspeed to > 61,000 rpm, it did not trip on overspeed, but tripped on high vibration, apart from inadequacy of intrumentation to detect impending overspeed tripping, the IGV was later checked & confirmed OK. What caused it to overspeed? Any comment/input very much appreciated. TQ

 

[nickelkid]

Was the compressor loaded?

 

[arbainmahmood]

Yes, it was partly loaded, when operator was manually loading unit C, unit-D was then switched to 'Auto' mode. No record as at what pressure or temp when it went up overspeed.

 

[nickelkid]

You have identified the need for adequate instrumentation. The cost of this failure should justify the expense.

 

[maddocks]

Kind of sounds like a surge case, but it happened awful fast. Do you have any speed trending on the unit?