Troubleshooting of Copes Vulcan bypass valve

Complete guide for on-site debugging and troubleshooting of Copes Vulcan turbine bypass system

In thermal power generation, combined cycle, and cogeneration plants, the turbine bypass system is a key equipment that connects the boiler with the turbine, reheater, and condenser. It not only undertakes the steam bypass function during unit start-up, shutdown, and load shedding, but also is responsible for quickly reducing the main steam pressure and temperature to an acceptable level for downstream equipment, while protecting the reheater tube bundle from being burned out. As a global steam regulation equipment supplier with over 90 years of experience, Copes Vulcan's HP (high pressure) and LP (low pressure) bypass systems are widely used in the industry. However, as the operating years of the unit increase, problems such as blockage of bypass valves, erosion of internal components, delayed response of actuators, and inaccurate temperature control gradually become apparent. This article is based on the official technical information and on-site service practice of Copes Vulcan, systematically sorting out the selection points, typical fault causes, and standardized troubleshooting methods of turbine bypass valves, providing a practical reference manual for thermal control and maintenance engineers in power plants.

Function of turbine bypass system and Copes Vulcan product system

Modern steam turbine bypass systems typically adopt a two-stage configuration of high-pressure bypass (HP bypass) and low-pressure bypass (LP bypass), and some supercritical units also have a medium pressure bypass. Its main functions include:

Decoupling debugging of boiler and turbine: allowing the boiler to operate at full load (100% capacity bypass) before the turbine is connected to the grid, reducing start-up time.

Cold, warm, and hot start-up metal temperature matching: By reducing temperature and pressure, the steam parameters are synchronized with the turbine metal temperature to reduce thermal stress.

Prevent boiler overpressure during load shedding or tripping: Avoid damage to the sealing surface and loss of condensate caused by the spring type safety valve tripping.

Cool the final stage superheater during sliding pressure operation.

Maintain the cooling flow rate of the reheater to prevent dry burning.

Maintain stable boiler outlet pressure at partial load.

Protect the condenser from the impact of high temperature and high pressure steam.

Copes Vulcan offers a variety of valve series for different application scenarios:

Full name of valve model, typical application, pressure rating, structural characteristics

DSCV Direct Steam Conditioning Valve HP/LP bypass, back pressure machine bypass up to Class 4500 forged steel structure, customizable temperature and pressure reduction integration, online replacement of internal components

TE-PRDS Top Entry Pressure Reducing&Desuperheating Medium Pressure Auxiliary Bypass, Temperature and Pressure Reduction Station Class 150~2500 Cast Valve Body, Top mounted Interior, Maintenance without Disassembling Valve Body

PRDS Pressure Reducing&Desuperheating Conventional Temperature and Pressure Reducing Station Class 600~2500 Classic Casting Structure, Cage Guidance, Multi level Noise Reduction Optional

HP Bypass Valve High pressure bypass valve Main steam to cold reheat maximum Class 4500 forged steel, multi-stage HUSH noise reduction orifice plate+outlet diffuser, cold end water spray

LP Bypass Valve: Low pressure bypass valve for reheating steam to condenser, made of forged steel up to Class 900 with a large flow area and optional discharge/diffusion pipes

The vast majority of faults encountered by engineers on site are concentrated in four aspects: the actuator, internal component erosion, cooling water regulation, and control logic of the above-mentioned valves. Expand one by one below.

Typical faults and on-site handling of HP bypass valve

The HP bypass valve is the most stringent valve in the system, which requires the main steam (up to 220 bar/590 ° C) to be instantly depressurized and cooled to cold reheat conditions (usually around 40 bar/300-400 ° C). When the steam turbine trips, the valve must be fully opened within 1-2 seconds to prevent the boiler safety valve from tripping.

2.1 Common Fault Phenomena and Causes

Possible causes of fault phenomena and diagnostic methods

The valve cannot be quickly opened due to insufficient oil/gas pressure in the actuator; Pilot valve jamming; Mechanical spring fatigue inspection of HPU accumulator nitrogen pressure (normally 60%~80% of system pressure); Conduct a full stroke step response test

After opening, the pressure fluctuation is mostly caused by blockage or erosion of the HUSH orifice plate; The sealing ring of the balance plug is damaged. Disassemble and inspect the internal components, and measure the pressure before and after each throttle stage; Check the sealing surface of the valve seat

The outlet temperature exceeds the limit and the cooling water nozzle is blocked; Linear difference of cooling water regulating valve; The low water level in the hot well causes the suction port to be empty. Check the corresponding nozzle status for the cooling water introduction method (suction spray/mechanical atomization/steam atomization); Verify the Cv characteristics of the cooling water valve