A power plant is several fluid systems sharing one site: cooling water, condensate, feedwater, steam, fuel and flue gas. Temperature and thermal cycling decide the valve in the steam cycle, while volume and reliability dominate the water side.
Request a Quote →Start with the water side, because it holds the largest valve count by diameter. Circulating water pumps draw from a river, cooling tower basin or the sea and push water through the condenser, then back to the cooling tower or outfall. Every pump has a suction and discharge isolation valve and a discharge check valve, and the condenser has isolation on both the inlet and outlet water boxes so a tube can be plugged without draining the whole circuit. These lines are large and low-pressure, and they are the classic territory of the butterfly and gate valve. Where the intake water carries debris, screens and strainer branches are fitted with knife gate valves.
The condensate and feedwater train is a different problem. Condensate is pumped from the hotwell through polishing and low-pressure heaters, then through the deaerator and the boiler feed pumps into the economiser and the boiler. Each heater has isolation and bypass, each pump has suction, discharge and minimum-flow recirculation valves, and the boiler feed line carries a non-return valve and a feedwater control valve. Pressures are high, temperatures climb along the train, and the control valves are expected to modulate continuously.
On the steam side, superheated steam leaves the boiler or heat recovery steam generator and passes through the main stop valve and the governor valves to the turbine. Between the superheater and the reheater, and around the turbine, sit the isolating valves, the bypass and warm-up lines, the drain valves and the safety-related isolation on the extraction and auxiliary steam branches. This is the highest-temperature part of the plant and the part where material selection is least forgiving.
A combined-cycle plant adds a gas turbine and a heat recovery steam generator, which brings its own drum, attemperator and bypass stack valves. A biomass plant keeps the same steam cycle but adds an abrasive and variable fuel handling system and an ash circuit, both of which favour abrasion-resistant isolation valves, plus flue-gas treatment equipment where corrosion rather than temperature sets the material choice.
| Valve Type | Typical Duty in a Power Plant | Practical Note |
|---|---|---|
| Butterfly | Circulating and cooling water, condenser water boxes, cooling tower isolation, auxiliary water | The workhorse of the water side. Large diameters, low head loss when open, cheap to actuate. |
| Gate | Main steam isolation, feedwater isolation, pump suction and discharge, drain lines | Full-bore, suited to isolation rather than regulation. Body and trim grade must follow the design temperature. |
| Globe | Throttling duty, drain and vent lines, small-bore steam isolation, bypass | Better regulation than a gate at the cost of pressure drop. Common on small-bore high-pressure lines. |
| Ball | Instrument and sampling isolation, chemical dosing, fuel gas isolation, quick shut-off | Quarter-turn and tight sealing. Metal-seated designs suit higher temperatures than soft seats. |
| Control | Feedwater regulation, attemperator spray, condensate and heater level, steam temperature control | Sized from Cv, pressure drop and turndown. Cavitation and flashing are common on let-down duty. |
| Check | Pump discharge, boiler feed non-return, extraction and auxiliary steam branches | Closing characteristic governs water hammer on trip. Dual-plate closes fast; swing has lower pressure loss. |
| Knife gate | Ash and slag handling, fuel and limestone handling, flue-gas desulphurisation slurry, screen branches | Built for solids and abrasive slurries. Liner and gate hardness decide service life. |
| Triple-offset butterfly | High-cycle isolation on cooling water and auxiliary systems, large-diameter water headers | Metal seat with a torque-based seal, chosen where cycle counts are high and a soft seat would wear. |
Cooling water. Ductile iron or cast iron bodies with an epoxy lining and EPDM or neoprene seats are usual for freshwater circuits. When the cooling medium is seawater, the same logic as a desalination plant applies and corrosion-resistant alloys or lined bodies become necessary.
Condensate and feedwater. Demineralised water is aggressive in a different way from seawater: it is low in dissolved solids and readily picks up iron and copper, so corrosion products matter as much as wall loss. Carbon steel bodies are common, with stainless steel used on smaller and more critical lines. The dissolved oxygen level and the water chemistry regime set the trim choice.
Steam. Carbon steel such as ASTM A216 WCB serves moderate steam temperatures, and chrome-molybdenum grades such as WC6 and WC9 are used as temperature rises because they retain strength better and resist graphitisation. Austenitic stainless steels are specified for high-temperature or corrosive service, and hard-faced trim is used where erosion from wet steam or entrained particles is expected. Above the creep range, material selection is a design decision made by the plant engineer against the piping specification.
Flue gas and ash. Corrosion and abrasion dominate. Knife gate valves with a hardened or lined gate handle ash and slurry, and flue-gas desulphurisation circuits use corrosion-resistant alloys or rubber-lined bodies because the slurry is both acidic and abrasive.
Bolting, gaskets and packing. These are the details that fail first on a cycling plant. At elevated temperature, bolting must match the thermal expansion of the body and flange, and gasket and packing materials have their own temperature limits. Graphite-based products are common at high temperature, and PTFE is restricted to the lower end of the range.
Power projects work from a piping specification and a valve specification that reference a defined standard set. ASME B16.34 provides pressure-temperature ratings for valves. API 600 covers steel gate valves for the petroleum and gas industries and is widely accepted on power work, and API 602 covers compact steel gate valves. API 609 and EN 593 cover butterfly valve design. API 598 and ISO 5208 govern shell and seat pressure testing, and ISO 5208 defines the allowable leakage rates by class. Flange drilling follows ASME B16.5 for smaller sizes and ASME B16.47 for larger ones, with EN 1092 used on metric projects. Materials are specified to ASTM grades and, at higher temperatures, to the applicable piping specification.
Utility projects also carry non-destructive examination requirements, usually applied to pressure-containing castings and to welds, and often naming radiographic, magnetic particle or dye penetrant inspection. Some projects specify a fire-safe design for fuel gas and oil systems, and those requirements are described in standards such as API 607 and API 6FA. Where a specification names a fire test, an anti-static requirement or a material approval, raise it at enquiry stage: these relate to a specific product configuration and are available on request for qualified orders. Reguvale holds ISO 9001 quality-system certification and SGS-CSTC factory audit reports, and we confirm the achievable specification in writing before the order.
The standard set is a mill test certificate to EN 10204 3.1 traceable to the heat number, hydrostatic and seat test reports per API 598, and dimensional inspection records against the approved drawing. Power projects usually add to this. Non-destructive examination reports, hardness test records for hard-faced trim, and where a project specifies it, material verification of the body and trim against the mill certificate. Coating and lining records apply on the cooling water side.
Two practical points make the paperwork easier. First, the design temperature and pressure of each line determine the pressure-temperature rating, and that determination needs to happen at enquiry stage, not after the mill certificate has been issued. Second, utility projects commonly use third-party inspection with a witness point on the pressure test, and the visit has to be scheduled against production. Tell us the inspection regime with the enquiry.
Choosing an elastomer seat by habit on a hot line. Seats have temperature limits, and a soft seat specified for a steam drain or a hot condensate line will harden and lose sealing. Metal-seated designs exist for exactly this reason.
Ignoring thermal cycling. A cycling plant that starts and stops daily puts the valve through expansion and contraction that a base-load plant does not. Bolting, gaskets and packing deserve the same scrutiny as the body.
Sizing control valves from the line diameter. A feedwater or spray control valve is sized from Cv, the available pressure drop and the turndown the control loop needs, and cavitation on the let-down duty has to be checked.
Treating check valves as a commodity item. The closing characteristic determines the water hammer on pump trip, and on a large circulating water pump that is an equipment-protection decision.
Specifying a gate valve for regulation. A gate valve is an isolation device. Throttling it partially open damages the seat and the disc, and a globe or control valve belongs on that duty.
Neglecting the actuator environment. Outdoor pipe racks and turbine halls see heat, vibration and weather, so enclosure rating, ambient temperature and the fail position of the actuator need to be specified with the valve.
Large-diameter butterfly and gate valves dominate, because cooling water lines are big, the pressures are modest and the valves mostly sit open. Circulating water pump discharge, condenser inlet and outlet, and cooling tower isolation are typical butterfly duties. Where the water carries debris, a knife gate is used on the strainer and screen branches.
Carbon steel such as ASTM A216 WCB is common for moderate-temperature steam and feedwater, with chrome-molybdenum alloys like WC6 and WC9 used as temperature rises, and stainless steels for high-temperature or corrosive duties. Trim is usually stainless or hard-faced, and the pressure-temperature rating follows ASME B16.34. The correct grade depends on the design temperature and pressure of the specific line.
Because reverse flow is a safety and equipment-protection issue. Check valves protect pumps from backflow on trip, prevent steam from reversing into a stopped turbine branch, and isolate feedwater from the boiler. Swing and dual-plate designs are the usual choices, and the closing characteristic matters because it determines the water hammer on pump trip.
ASME B16.34 for pressure-temperature ratings, API 600 and API 602 for gate valves, API 598 and ISO 5208 for shell and seat testing, and API 609 or EN 593 for butterfly valves. Flange drilling follows ASME B16.5 or B16.47, and material grades follow ASTM. Power projects frequently add non-destructive examination requirements, and pressure-containing castings may be subject to radiographic or magnetic particle inspection.
A mill test certificate to EN 10204 3.1 traceable to the heat number, hydrostatic and seat test reports to API 598, dimensional inspection against the approved drawing, and where specified, non-destructive examination reports and hardness test records for the trim. Third-party inspection and witnessed testing are common on utility projects.
Biomass plants handle more abrasive and variable fuel, so fuel handling, ash and flue-gas circuits place more emphasis on abrasion-resistant knife gate and isolation valves. The steam cycle itself is similar to a conventional thermal plant. Where flue gas is corrosive, corrosion-resistant alloys or coatings are used on the wetted parts.
Butterfly Valves · Electric Butterfly Valves · Triple-Offset Butterfly Valves · Gate Valves · Globe Valves · Control Valves · Ball Valves
Related: Water Treatment · Desalination · All Applications · Markets We Serve · Certificates & Compliance
Tell us the system, the medium, the design pressure and temperature, the size, the connection standard and the inspection regime the project specifies. We reply within 24 hours with price, lead time and the documentation we can provide.
Request a Quote → Contact Us →