Troubleshooting of Copes Vulcan bypass valve

High temperature thermal oxidation caused by leakage of valve stem and packing leads to carbonization of packing; Replace the flexible graphite packing due to surface strain on the valve stem and check the hardness of the valve stem (recommended ≥ 40HRC)

Internal leakage valve seat/disc sealing surface erosion after closure; Failure to close properly (mechanical limit drift of actuator), pressure test or ultrasonic leak detection; Re calibrate the actuator stroke

2.2 Key Internal Component Inspection Points

The multi-stage HUSH noise reduction orifice plate is the core of the HP bypass valve. During on-site maintenance, it is important to focus on checking:

Whether there are cracks or corrosion at the edge of each throttle hole (especially when the steam temperature exceeds 540 ° C, the nickel based alloy overlay may experience thermal fatigue).

Is the fastening bolt between the orifice plates loose (due to high temperature creep causing a decrease in pre tightening force).

If obvious erosion is found, it is recommended to replace it with a new orifice plate welded with cobalt based alloy (Stellite) and check the upstream filter (the aperture should not exceed 1mm).

The selection of cooling water introduction method directly affects the stability of outlet temperature. Based on on-site experience:

Aspiration: using steam flow rate to generate negative pressure and suck in cooling water, suitable for high pressure difference and low water flow conditions, with no moving parts and strong anti clogging ability. The common fault is scaling of the suction nozzle, which requires regular chemical cleaning.

Mechanical spray: Water is atomized through multiple nozzles, suitable for medium water volume. The nozzle is prone to clogging and requires the installation of a Y-shaped filter.

Steam atomization: using auxiliary steam to atomize water, with the widest adjustment ratio (up to 50:1), but the system is complex and requires an additional steam source. Malfunctions often occur in the fluctuation of atomization steam pressure or leakage of check valves.

2.3 Failure mode of actuator (HP bypass)

HP bypass valves typically require fail open, meaning that the valve should automatically open to protect the boiler when power is lost. There are three types of executing agencies:

Pneumatic piston+spring reset: The most common fault is spring fatigue causing the fully open time to exceed the standard (normally ≤ 2 seconds). Inspection method: Cut off the gas source and measure the time from closing to fully opening the valve. If it exceeds 3 seconds, replace the spring or increase the spring preload.

Pneumatic+accumulator: Damaged accumulator skin or nitrogen leakage can lead to insufficient storage capacity. Check the nitrogen pressure every six months and replace the bladder if the pressure drops by more than 20%.

Electro hydraulic actuator (HPU centralized or self-contained): Malfunctions often occur due to servo valve blockage, high pressure difference in high-pressure filter element, and hydraulic oil emulsification. On site oil samples should be taken to check the acid value and moisture content (phosphate ester fire-resistant oil should control moisture content<0.1%).

Special issues of LP bypass valve and condenser protection

The inlet of the LP bypass valve is reheated steam (usually at a pressure of several kilograms to tens of kilograms and a temperature of 300~500 ° C), and the outlet is negative pressure of the condenser (about 0.05 bar abs). The steam specific volume expands violently, and the valve size is often very large (such as DN600~DN1000). The faults mainly focus on high noise, vibration, and cooling water suction issues generated under high flow rates.

3.1 Vibration and Fracture of Dump Tube

After the LP bypass valve, a discharge pipe is usually installed into the condenser throat, with a large number of small holes on the pipe wall ("small hole technology" is used for noise reduction). Common on-site issues:

Cracking of discharge pipe weld: Due to steam reaction force and thermal expansion displacement, fatigue fracture occurred at the connection between the discharge pipe and the condenser.

Small hole blockage: During shutdown, rust or foreign objects enter, causing an increase in back pressure and insufficient flow during operation.

Cavitation: Fish scale erosion pits appear on the inner wall of the discharge pipe, usually in the wet steam zone.

Solution:

Use bellows expansion joints or sliding guide brackets at the connection between the discharge pipe and the condenser to release thermal displacement.

The diameter of the small hole should not be less than 8mm, and its orientation should avoid the pipe wall and condenser bundle (to avoid direct flushing).

Use an endoscope to inspect the inside of the discharge pipe and clean up debris during each minor repair.

3.2 Dilution water cannot be effectively mixed

Due to the limited internal space of the condenser, there is often not enough straight pipe section after the LP bypass valve to allow steam to fully mix with the desalinated water. Copes Vulcan recommends two solutions:

A diffuser cartridge is installed at the valve outlet, and the final pressure reduction and cooling are achieved through multi-stage expansion plates.