Real Story: Solving Slow Vessel Fill Issues During New Plant Commissioning
During the commissioning of a new chemical plant, the operational team quickly noticed that the vessel fill rate was far slower than expected. This delay threatened to disrupt the testing and validation schedule. They immediately called on the E&I start-up team to investigate the root cause. After a thorough and systematic investigation, the team discovered a surprising culprit: a piece of cloth rag lodged inside the control valve, restricting the flow.
1. The Problem: Slow Vessel Fill Rate
1.1 Observing the Issue
- Operators observed that the vessel was taking far longer to fill than the design specifications indicated.
- This delay raised concerns about potential equipment malfunctions or installation errors.
1.2 Suspected Causes
- The team considered several possible explanations:
- A malfunctioning control valve.
- Incorrect flowmeter calibration.
- A blockage or restriction in the pipeline.
The issue required immediate attention, so the team moved quickly to investigate further.
2. The Investigation
2.1 Checking the Flow Rate
The team began by reviewing the process flow diagrams (PFDs) to confirm the expected flow rate. They then compared these values with the flowmeter readings, which showed a much lower flow rate than expected. This discrepancy pointed to a restriction somewhere in the system.
2.2 Inspecting the Control Valve
Next, the team focused on the control valve, which regulated the flow into the vessel. They verified the valve’s position through its positioner data and found that it was fully open. However, despite the valve being open, the flow remained restricted, signaling a possible issue within the valve itself.
2.3 Testing with a Bypass
To isolate the problem, the team opened a manual bypass valve to direct flow around the control valve. The flow instantly improved, confirming that the issue was confined to the control valve assembly.
3. The Root Cause: A Cloth Rag Blockage
3.1 Discovering the Obstruction
The team removed the control valve from the pipeline for inspection. Upon disassembly, they discovered a cloth rag lodged in the valve body, partially blocking the flow path. The rag had likely been left behind during pipeline cleaning or valve maintenance and was inadvertently introduced into the pipeline during installation.
3.2 Analyzing the Cause
This obstruction highlighted a common but avoidable mistake: using temporary materials, such as cloths, to wipe or protect components during construction without ensuring their removal afterward.
4. Resolving the Issue
4.1 Clearing the Valve
The team carefully removed the cloth rag and thoroughly cleaned the valve. After inspecting for damage, they determined the valve was still in good condition and reinstalled it.
4.2 Verifying the Solution
After reinstallation, the team tested the flow rate, which now matched the design specifications. They confirmed the issue was resolved by running the system under various operating conditions, and no further restrictions were detected.
4.3 Preventing Future Occurrences
Recognizing the need for better preventive measures, the team updated the pipeline cleaning and inspection procedures to ensure similar problems wouldn’t arise in the future.
5. Key Takeaways
This incident provided several critical lessons for commissioning and operations teams:
5.1 Maintain Cleanliness
Debris, such as cloth rags, can easily cause significant disruptions if left behind during construction or maintenance. Thorough flushing and inspection of pipelines are essential before commissioning.
5.2 Follow a Systematic Approach
The team’s step-by-step troubleshooting process was instrumental in identifying the problem. By isolating each potential cause—flowmeter, control valve, and pipeline—they efficiently pinpointed the issue.
5.3 Collaborate Across Teams
The collaboration between the operations and E&I start-up teams ensured quick resolution. Effective communication and teamwork allowed them to address the problem without significant delays.
6. Recommendations for Future Projects
| Action | Why It Matters |
|---|---|
| Flush Pipelines Thoroughly | Removes debris and ensures clean operation of control valves and instruments. |
| Inspect Critical Components | Verifies that control valves and other devices are free of obstructions. |
| Use a Pre-Startup Checklist | Ensures all pipelines, valves, and instruments are inspected before commissioning. |
| Monitor Flow in Real Time | Detects deviations early, enabling quick intervention during commissioning. |
7. Conclusion
This real-world incident demonstrates how small oversights during construction or maintenance can lead to significant commissioning challenges. The discovery of a cloth rag inside the control valve illustrates the importance of cleanliness and meticulous pre-commissioning procedures.
By acting quickly and using a systematic approach, the team resolved the issue and restored the system to its design performance. This experience underscores the value of thorough inspections, effective troubleshooting, and cross-team collaboration in ensuring successful plant commissioning.