What is the difference between P91 and P92 material

P91 and P92 are both advanced chromium-molybdenum heat-resistant alloy steels developed for high-temperature and high-pressure applications. The primary difference is that P92 contains additional tungsten (W) and optimized alloying elements, which provide higher creep strength, better long-term thermal stability, and improved performance at temperatures above 600°C. While P91 is widely used in conventional and supercritical power plants, P92 is often selected for ultra-supercritical boilers and steam piping systems where higher efficiency and longer service life are required.

In simple terms, P91 offers an excellent balance of performance and cost, while P92 delivers superior high-temperature strength for the most demanding operating conditions.

 

P91 vs P92 Comparison Table

Property	P91	P92
ASTM Grade	ASTM A335 P91	ASTM A335 P92
Steel Type	9Cr-1Mo-V-Nb	9Cr-0.5Mo-1.8W-V-Nb
Chromium Content	8.0–9.5%	8.5–9.5%
Molybdenum Content	0.85–1.05%	0.30–0.60%
Tungsten Content	None	1.5–2.0%
Minimum Tensile Strength	585 MPa	620 MPa
Minimum Yield Strength	415 MPa	440 MPa
Maximum Service Temperature	Approximately 600°C	Approximately 620–650°C
Creep Strength	Excellent	Superior
Cost	Lower	Higher
Typical Application	Supercritical Power Plants	Ultra-Supercritical Power Plants

 

Why Was P92 Developed?

As power generation technology advanced, power plants required materials capable of operating at higher temperatures and pressures to improve thermal efficiency.

Although P91 significantly improved performance compared with traditional grades such as P22, engineers found that long-term creep resistance became a limiting factor in ultra-supercritical units.

To address this challenge, P92 was developed by modifying the P91 alloy system and adding tungsten.

The result was a material with:

• Higher creep rupture strength
• Better long-term thermal stability
• Improved oxidation resistance
• Longer service life under extreme conditions

This allows power plants to operate at higher steam temperatures while maintaining safety and reliability.

 

Chemical Composition Difference Between P91 and P92

ASTM A335 P91

Element	Content (%)
Carbon	0.08–0.12
Chromium	8.0–9.5
Molybdenum	0.85–1.05
Vanadium	0.18–0.25
Niobium	0.06–0.10

ASTM A335 P92

Element	Content (%)
Carbon	0.07–0.13
Chromium	8.5–9.5
Molybdenum	0.30–0.60
Tungsten	1.5–2.0
Vanadium	0.15–0.25
Niobium	0.04–0.09

The most significant difference is the addition of tungsten in P92, which greatly enhances creep resistance at elevated temperatures.

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Mechanical Properties Comparison

Mechanical properties are one of the main reasons engineers upgrade from P91 to P92.

Property	P91	P92
Tensile Strength	≥585 MPa	≥620 MPa
Yield Strength	≥415 MPa	≥440 MPa
Elongation	≥20%	≥20%
Hardness	Controlled by Specification	Controlled by Specification

The higher strength of P92 allows designers to reduce wall thickness in certain applications, lowering overall system weight while maintaining pressure capability.

 

 

Heat Treatment Requirements

Both materials require careful heat treatment to achieve their specified properties.

P91 Heat Treatment

Normalizing: 1040–1080°C

Tempering: 730–800°C

P92 Heat Treatment

Normalizing: 1040–1080°C

Tempering: 750–780°C

Because P92 relies heavily on precipitation strengthening mechanisms, precise heat treatment control is particularly important.

 

P91 vs P92 Creep Strength

For high-temperature piping systems, creep strength is often the deciding factor.

Creep is the slow permanent deformation of a material exposed to stress at elevated temperatures over long periods.

Compared with P91, P92 offers:

Higher creep rupture strength

Better dimensional stability

Longer design life

Higher allowable stress values

This makes P92 the preferred choice for ultra-supercritical power stations operating above 600°C.

 

Applications

Applications of P91

Main steam piping

Reheater piping

Boiler headers

Refinery process piping

Combined-cycle power plants

 

Applications of P92

Ultra-supercritical boiler tubing

High-temperature steam piping

Advanced power generation systems

High-efficiency thermal power plants

 

Can P92 Replace P91?

Technically, P92 can often replace P91 because it provides superior high-temperature performance.

However, replacement decisions should consider:

Design code requirements

Welding procedures

Heat treatment requirements

Project budget

Material availability

For many conventional projects operating below 600°C, P91 remains the most economical solution.

For ultra-supercritical applications, P92 is often the preferred material.

 

Which Material Should You Choose?

Choose P91 when:

✓ Operating temperatures are below approximately 600°C

✓ Cost control is important

✓ Proven performance is sufficient

✓ Standard supercritical service conditions apply

 

Choose P92 when:

✓ Operating temperatures exceed 600°C

✓ Maximum creep resistance is required

✓ Long-term service life is critical

✓ Ultra-supercritical power generation is involved

 

A335 P91 steel pipe MTC

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FAQ

What is the main difference between P91 and P92?

The primary difference is the addition of tungsten in P92, which provides higher creep strength and improved high-temperature performance.

 

Is P92 stronger than P91?

Yes. P92 has higher tensile strength, yield strength, and creep rupture strength than P91.

 

Can P92 replace P91?

In many cases yes, but engineering approval is required because welding procedures, heat treatment requirements, and project specifications may differ.

 

Why is P92 more expensive?

P92 contains additional alloying elements such as tungsten and requires stricter manufacturing controls, resulting in higher production costs.

 

Which material is used in ultra-supercritical power plants?

P92 is commonly selected because of its superior high-temperature strength and creep resistance.