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 |
| 1 | Upstream & Downstream 8×3” pipe reducer small-bore dia measured in the field | 60 | 60 |
| 2 | Ball Bore dia | 80 | 80 |
| 3 | Valve inlet and outlet nozzle bore dia | 80 | 60 |
Author Conclusions
- V2 60 mm nozzle bore dia reduces the system already marginal flow capacity even below requirement; hence the surge and near miss compressor wreck
- 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:
- The one size lower than pipeline 6” CV meets the pipeline code.
- It was problem free during for over 6 years, when author left the plant; maybe it was problem free forever
- 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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