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 an Upper HP support flange with metal bellows lose?

At the 460 °C reference temperature, the combined support flange and metal bellows case is 47.174 kW bare, 1.887 kW with insulation and 45.287 kW retained for one selected scope. Temperature and quantity remain editable.

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

Yes, when the removable module is designed around the component's inspection points, drainage, movement envelope and support clearances. Final surface temperature and thickness remain project checks.

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.

Project-based HRSG component results

Direct answer: there is no defensible “typical kW per HRSG component” without geometry and temperature. The table below gives one-element reference cases for the four selectable HRSG areas. Temperature and site count remain editable in Your savings.

HRSG area	Reference °C	Bare	With insulation	Retained
Upper HP line · support flange with metal bellows	460	47.174 kW	1.887 kW	45.287 kW
Upper IP line · metal bellows	180	4.672 kW	0.187 kW	4.485 kW
Lower HP line · metal bellows	420	5.160 kW	0.206 kW	4.953 kW
Lower IP line · metal bellows	200	1.939 kW	0.078 kW	1.862 kW

One element per row; ambient 27.7 °C, wind 3.1 m/s, explicit convection and radiation, public reduction capped at up to 96%. Use Your savings to change temperature, enter the site count and calculate annual heat, steam-cycle electrical equivalent, fuel, gas and CO₂.

Can these components be insulated?

Yes, when the removable module is engineered around the component. Pumps, valves, heat exchangers, doors and expansion joints are often left bare because they need maintenance access, inspection or movement clearance. Inzonex Modular Insulation uses identified removable modules and quick-release retention so the component can be exposed and the same module refitted. Insulation thickness, drainage, support clearances and the ≤45 °C outer-surface target are then checked for the actual project duty.

HRSG 3D Scope Map + Your savings → 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?

Calculate the retained kW for each distinct geometry, multiply by verified quantity and operating hours, then choose one plant pathway. The public planning output is capped at up to 96%; financial value and payback appear only after the operator enters its own energy rate and installed cost.