Compressor Anti-Surge Control near-miss incident

Root Cause Analysis (RCA): There is a near-miss incident reported on a compressor anti-surge control.

Article Type:Root Cause Analysis (RCA)
Category:Mechanical
Equipment Type:High Speed, Hi KW Major Rotating Machines
Author:S. Raghava Chari

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of one or two decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

Compressor Anti-Surge Control near-miss incident

Compressor (K-601) HP case anti-surge control 3” 1500 # RTJ flanged ball valve (V1) passed excessively and leaked heavily at the stem after 2 service years.

The all welded up V1 permits no dissemble; hence no repair either. The plant engineer found the same company made 3”x1500 # butt weld end valve (V2).

On his request, the workshop welded flanges to V2. V2 went online. On start, K‑601 surged heavily; an alert operator tripping the turbine averted K‑601 wreck.

The author root cause analyzed the near-miss incident to resume production ASAP and surge prevention.    

Author RCA solution

The author got V2 taken out, compared V1.and V2 placed side by side.

His observations are:

#Observations  V1
V2  
1Upstream & Downstream 8×3” pipe reducer small-bore dia measured in the field6060
2Ball Bore dia8080
3Valve inlet and outlet nozzle bore dia8060

Author Conclusions

  1. V2 60 mm nozzle bore dia reduces the system already marginal flow capacity even below requirement; hence the surge and near miss compressor wreck
  2. Catalog shown V2’s 70% V1 flow capacity confirms the author’ deduction

Immediate Solution

He checked and found even after nozzles bore increase to 80 mm, V2 wall thickness adequate for 1500 # rating. With nozzles bored to 80 mm dia V2 the compressor did not surge. 

Permanent Solution

The 3” valve on 8” line is a potential pipeline strength reducer. Hence, he selected a 6” globe design CV for the service.

Permanent solution Benefits

Permanent solution benefits are:

  1. The one size lower than pipeline 6” CV meets the pipeline code.
  2. It was problem free during for over 6 years, when author left the plant; maybe it was problem free forever 
  3. Just bonnet dissemble and few inexpensive elastomer changes would restore the new valve leak-tightness, unlike the former ball valve.

Author: S. Raghava Chari

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