Philippines Coal Power Plant Replaces Soft-Seat Butterfly Valve for Steam Piping at 425°C to Metal Hard buttefly valve

Introduction: Several coal-fired power plants in the Philippines have experienced seat aging and increased internal leakage after 1–2 years of using soft-seat butterfly valves in high-temperature steam lines.

Pain Point: Soft-Seal Failure Mechanism Under High-Temperature Steam

In auxiliary steam systems of coal power plants (e.g., soot blower lines, tracing lines), media temperatures often reach 350°C–425°C. Conventional soft-seat butterfly valves using PTFE, EPDM, or NBR seats have the following limitations:

• PTFE seat: Long-term service limit around 230°C. Above this, material softening and creep reduce sealing contact pressure.

• Elastomeric rubber seat: Accelerated aging above 150°C, loss of resilience, and permanent deformation after cycling.

Typical field failures include: audible steam leakage when the valve is closed, normal actuator torque but unable to shut off completely, and seat charring or carbonization found during disassembly.

Technical Parameters of the Alternative Solution: Evidence of Hard-Seal Butterfly Valve Stability at 425°C

The selected electric hard-seal butterfly valve (wafer type, body WCB/SS304, disc SS304) provides the following verifiable parameters:

The hard-seal structure relies on contact pressure between the metal seat and disc to achieve shut-off, independent of elastic material deformation. Hence it maintains consistent sealing contact pressure during temperature cycling.

Working Principle and Advantages of Electric hard-sealed butterfly valve .pdf

The body and seat are integrated components. The seat sealing surface is overlaid with temperature-resistant and corrosion-resistant alloy material. A multi-layer flexible laminated seal ring is fixed on the disc. Compared with traditional butterfly valves, this type of valve offers high temperature resistance, easy operation, frictionless opening/closing, and compensates sealing through increased torque from the transmission mechanism when closing, thus improving sealing performance and extending service life.

① The unique triple offset design enables frictionless transmission between sealing surfaces, extending valve service life.
② Elastic sealing generated by torque.
③ The ingenious wedge design provides an automatic “tighten-as-you-close” sealing function, with compensation and zero leakage between sealing surfaces.
④ Compact, lightweight, easy to operate, and convenient for installation.
⑤ Pneumatic or electric actuation can be configured per user requirements to meet remote and programmatic control needs.
⑥ Various connection types: wafer, lug, flanged, butt-welded.

Installation and Selection Considerations

3.1 Actuator Torque Sizing

In steam lines, high temperature causes clearance changes between stem and bushing. When using SONGO series electric actuators, match valve torque with a safety factor (typically 1.3–1.5×). For a DN150 valve at 1.6 MPa operating pressure, calculated torque ≈120 N·m → select SONGO-30 (rated 300 N·m, providing margin).

3.2 Material Compatibility with Steam Quality

WCB body is suitable for saturated steam. If trace chlorides or acidic condensate exist, upgrade disc to SS316 (1Cr18Ni12Mo2Ti) to avoid pitting corrosion.

3.3 Mounting Orientation

For wafer-type hard-seal butterfly valves, the disc should open at an acute angle to the pipe axis to avoid high-velocity steam erosion on the seat back face. Typically install stem horizontally with actuator upright.

Operational Results and Maintenance Interval

After six months of replacement service:

• On-line seal test (bubble method) at 425°C steam showed no visible leakage.

• Actuator completed approximately 1,200 cycles with no torque drift.

• Stem packing (flexible graphite + PTFE composite) showed no external leakage.

Estimated maintenance interval extends from annual seat replacement (soft seal) to once every three years for packing inspection.

Conclusion

For high-temperature steam lines (≤425°C) in Southeast Asian coal power plants, electric hard-seal butterfly valves (metal seat + flexible graphite) provide a direct replacement when soft-seat valves fail. Selection must verify temperature, pressure, torque, and material compatibility. WCB body is not recommended for sulfur-bearing or acidic condensate services – SS316 should be used instead.