What are the HP, IP and LP steam temperatures and pressures in an HRSG?

A modern triple-pressure reheat HRSG typically runs: HP (high pressure) ≈120–165 bar, superheated to ≈540–565 °C (saturation ≈330 °C); IP (intermediate / reheat) ≈25–30 bar, hot-reheat to ≈540–565 °C (saturation ≈235 °C); LP (low pressure) ≈4–6 bar, ≈250–300 °C (saturation ≈150 °C). The exhaust gas enters at ≈600 °C and leaves the stack at ≈90–110 °C.

How much heat does a bare power-plant component lose?

At combined-cycle site conditions (27 °C ambient, 3.3 m/s wind, ASTM C680): a bare boiler/duct door (≈90 °C, 5 m²) ≈8 kW; a feed-water pump casing (160 °C, 12 m²) ≈46 kW; a heat-exchanger shell (150 °C, 4 m²) ≈14 kW; a safety valve (250 °C) ≈5 kW; a steam header (430 °C, 3 m²) ≈60 kW; a fabric expansion joint (280 °C, 1.6 m²) ≈15 kW. Removable insulation cuts each by 96–98%.

Can power-plant pumps, valves, heat exchangers and expansion joints be insulated?

Yes. These components are usually left bare because they need access for maintenance, inspection or movement, which fixed cladding cannot allow. Removable (modular) insulation jackets are made to fit each one, unzip in minutes for service and refit without damage — so the hot surfaces that are normally bare can be covered, saving fuel and bringing the surface to a touch-safe ≤45 °C.

Combined-Cycle Power Plant & HRSG Insulation: Temperatures, Process and Heat Losses

Q: What is a combined-cycle (CCGT) power plant?

A combined-cycle gas turbine (CCGT) plant burns natural gas in a gas turbine to make electricity, then captures the hot turbine exhaust (≈550–640 °C) in a heat-recovery steam generator (HRSG) to raise steam that drives a second, steam turbine. Using the same fuel twice lifts net efficiency to about 55–62%, versus ≈35–40% for a gas turbine alone.

Updated 10 June 2026 · ASTM C680 / ISO 12241 figures · by the Inzonex engineering team

A plain-English reference for combined-cycle (CCGT) power plants — how they work, the real HP / IP / LP steam temperatures and pressures, and how much heat every bare hot component loses (with the saving from insulating it).

What is a combined-cycle (CCGT) power plant?

Direct answer: a CCGT plant uses the same fuel twice. A gas turbine burns natural gas to generate power, and its hot exhaust (≈550–640 °C) is captured in a Heat-Recovery Steam Generator (HRSG) to raise steam that drives a second, steam turbine. This lifts net efficiency to ≈55–62%, against ≈35–40% for a gas turbine alone.

The process, stage by stage:

Gas turbine (Brayton cycle): compressed air + natural gas combust at ≈1,300–1,600 °C; the expanding gas spins the turbine and a generator. Exhaust leaves at ≈550–640 °C — still very hot.
HRSG (the heat exchanger): that exhaust passes through banks of finned tubes, giving up its heat to water and raising steam at up to three pressure levels. The gas cools to ≈90–110 °C at the stack.
Steam turbine (Rankine cycle): the HP, IP and LP steam expands through a steam turbine driving a second generator, then condenses and returns to the HRSG.

Because the HRSG and its steam pipework run hot and continuously (≈8,000 h/yr), every bare surface on it leaks heat that the bottoming cycle would otherwise have turned into electricity — which is why insulation directly affects the plant heat rate.

HRSG steam conditions — HP, IP and LP explained

A modern triple-pressure reheat HRSG raises steam at three pressure levels so it can extract heat from the exhaust across its full temperature range:

Circuit	Pressure	Steam temp (superheated)	Saturation temp
HP — high pressure	≈120–165 bar	≈540–565 °C	≈330 °C
IP — intermediate / reheat	≈25–30 bar	≈540–565 °C (hot reheat)	≈235 °C
LP — low pressure	≈4–6 bar	≈250–300 °C	≈150 °C
Exhaust gas path	—	≈600 °C inlet → ≈90–110 °C stack	—

HP drives the first turbine stage at the highest pressure and temperature; steam is then reheated and sent through the IP stage; the LP circuit captures the lowest-grade remaining heat. The external surface temperature of bare fittings, valves and expansion joints sits between these steam temperatures and the cooling gas path — typically 120–450 °C in practice.

Heat loss from bare power-plant components — and the saving

Direct answer: a single bare hot component on a power plant loses from under 1 kW (a small instrument) up to ≈60 kW (a 430 °C steam header) — continuously. Removable insulation cuts each by 96–98%. The table below gives typical figures per component (ASTM C680, 27 °C ambient, 3.3 m/s wind, 8,000 h/yr, natural gas).

Component	Surface °C	Bare loss	Saved	Energy/yr	CO₂/yr
Steam header	430	60.2 kW	59.2 kW	557 MWh	112 t
Feed-water pump casing	160	45.8 kW	44.1 kW	415 MWh	84 t
Fabric expansion joint	280	14.7 kW	14.5 kW	136 MWh	27 t
Heat exchanger / FW-heater shell	150	14.1 kW	13.6 kW	128 MWh	26 t
Boiler / duct door	90	8.4 kW	8.1 kW	76 MWh	15 t
Safety valve	250	5.0 kW	4.9 kW	46 MWh	9 t
Control / gate valve	280	3.2 kW	3.2 kW	30 MWh	6 t
Pipe flange (pair)	350	3.0 kW	2.9 kW	28 MWh	6 t
Sight glass / instrument	165	0.8 kW	0.8 kW	7 MWh	1.5 t

Per component, indicative for the sizes shown; energy is gas-fuel displaced at 85% boiler-equivalent, CO₂ at the IPCC natural-gas factor (0.202 t/MWh-fuel). A plant carries dozens of each — multiply by quantity. Run your own line items in the HRSG heat-rate calculator.

Can these components be insulated?

Yes — and that is exactly the gap Inzonex fills. Pumps, valves, heat exchangers, doors and especially expansion joints are normally left bare because they need to be accessed for maintenance, inspected regularly, or move with thermal expansion — none of which fixed, hard cladding allows. Removable (modular) insulation jackets are tailored to each component, secured with quick-release fasteners, unzipped in minutes for service and refitted with no damage. So the hot surfaces that are normally left uncovered — which are usually the biggest avoidable losses on the plant — can finally be insulated, cutting fuel use and bringing the outer surface to a touch-safe ≤45 °C.

HRSG heat-rate calculator → Whole-plant savings study → Get a per-element quote →

FAQ

What is a combined-cycle (CCGT) power plant?

It burns natural gas in a gas turbine for electricity, then captures the hot exhaust (≈550–640 °C) in an HRSG to raise steam for a second, steam turbine — using the fuel twice for ≈55–62% net efficiency, versus ≈35–40% for a gas turbine alone.

What does HP, IP and LP mean in a power plant?

They are the three steam pressure circuits of a triple-pressure HRSG: HP (high, ≈120–165 bar, ≈540–565 °C), IP (intermediate / reheat, ≈25–30 bar, ≈540–565 °C), and LP (low, ≈4–6 bar, ≈250–300 °C). Higher pressure and temperature steam does more work in the turbine.

Why is an HRSG so hot on the outside?

The HRSG carries steam from 150 to 565 °C and flue gas up to ≈600 °C. Wherever a surface — a valve, flange, pump, door or expansion joint — is left bare, it radiates and convects that heat into the plant, typically 1–60 kW per item, continuously.

How much can insulating the hot components save?

Each item saves 96–98% of its bare loss. A single 430 °C steam header saves ≈557 MWh/yr; a feed-water pump ≈415 MWh/yr; a 280 °C expansion joint ≈136 MWh/yr (≈27 t CO₂). Across the dozens of fittings on a typical HRSG this runs to hundreds of MWh and hundreds of tonnes of CO₂ per year, with payback usually under two years.