In PTA production plants within the chemical industry, the long-term stable operation of high-temperature and high-pressure steam control valves is crucial for the safety and economy of the entire process system. A PTA plant experienced control valve stem leakage in its steam regulation system. This valve leakage issue resulted not only in energy waste but also posed a threat to production safety. This GRAT case study will systematically analyze the cause of this valve leakage failure and provide a solution, offering a reference for valve selection and maintenance in similar working conditions.
Technical Specifications
Application: High-Temperature Steam Regulation System, PTA Chemical Plant
Medium: Superheated Steam
Body Material: WCB
Connection Type: Flanged
Actuator Type: Pneumatic
Operating Temperature: 385℃
Operating Pressure: 4.3MPa
Commissioning Date: December 2024
Installation Location: Steam Main Line, PTA Plant
After approximately six months of continuous operation, significant steam leakage was observed at the valve stem position of this control valve. The rate of valve leakage gradually increased over time, severely impacting production safety and environmental performance.
Troubleshooting & Analysis
Upon arrival, the GRAT technical support team disassembled the faulty control valve for inspection and identified the following issues:
- A severe leakage path was present in the stuffing box area.
- The original PTFE packing showed obvious signs of aging and hardening.
- Some packing rings were severely worn and had lost their elastic sealing capability.
Root Cause Analysis:
PTFE packing is prone to hardening and aging in high-temperature environments. Its sealing performance degrades significantly with large temperature fluctuations. The steam temperature in this application reached 385℃, far exceeding the normal service temperature limit for PTFE packing (around 200℃). This caused rapid packing failure, leading directly to the observed steam valve leakage.
Key factors influencing potential valve leakage include:
- Loose gland bolts with insufficient preload (e.g., due to long-term vibration)
- Worn or scratched valve stem surface (e.g., from solid particles in the medium)
- Incorrect packing installation methods (e.g., packing ring cuts not staggered)
- Use of packing material unsuitable for the service conditions (e.g., standard packing in high-temperature applications)
Solution & Implementation
Based on the specific site conditions, our technical personnel developed a targeted solution to stop the valve leakage:
Packing Material Replacement: All original PTFE packing was replaced with flexible graphite packing. This material offers a wide temperature range (-200℃ to +600℃), excellent self-lubrication, and superior thermal stability, making it ideal for preventing high-temperature valve leakage.
- Optimized Packing Structure: A combination of layered flexible graphite rings and intermediate reinforcing rings was used. This structure ensures reliable sealing performance while enhancing the overall strength of the packing set to combat valve leakage.
- Standardized Installation Procedure: The packing was installed layer by layer according to standard procedures, ensuring all ring cuts were staggered. A torque wrench was used to tighten the gland bolts evenly to the recommended torque.
After replacing the packing and optimizing the installation process, the control valve resumed stable operation. Following 72 hours of continuous monitoring using a portable volatile organic compound detector at multiple points around the gland, the valve stem seal showed zero leakage.
