What is P91/92 Steel?
P91 and P92 are high-temperature, high-pressure ferritic-martensitic steels used in power generation and other high-temperature applications. They are part of the family of advanced high-temperature steels (AHSS) that are designed to have superior mechanical properties at high temperatures.
P91 steel is a modified 9Cr-1Mo steel that contains 9% chromium and 1% molybdenum. It also has small amounts of vanadium, niobium, and nitrogen, which help to improve its creep strength and toughness. P92 steel is similar to P91 but has higher levels of molybdenum (up to 2%) and niobium (up to 0.08%). These additional alloying elements increase the high-temperature strength of the steel.
Both P91 and P92 steels are commonly used in steam power plants for components such as boiler tubes, steam pipes, and pressure vessels. They are also used in other high-temperature applications, such as gas turbines, petrochemical plants, and nuclear reactors.
One of the challenges with P91 and P92 steels is that they can be susceptible to a phenomenon called temper embrittlement. This is a form of degradation that can occur when the steel is exposed to temperatures in the range of 500-650°C for extended periods of time. To mitigate this, it is important to control the temperature and time of exposure during heat treatment and operation of components made from these steels.
A comprehensive summary of the composition and properties of P91 and P92 steels
- Composition: P91 and P92 steels are both modified versions of the 9% chromium-molybdenum (Cr-Mo) steels. The main elements in these steels include carbon (C), chromium (Cr), molybdenum (Mo), vanadium (V), and niobium (Nb). The composition of P91 steel typically contains around 9% Cr, 1% Mo, 0.2% V, and 0.1% Nb, while P92 steel has a slightly higher composition of 9% Cr, 1.85% Mo, 0.25% V, and 0.07% Nb.
- High-temperature strength: P91 and P92 steels exhibit excellent high-temperature strength, making them suitable for applications involving elevated temperatures and high pressure. They have a high yield strength and tensile strength, allowing them to withstand significant stresses at elevated temperatures.
- Creep resistance: One of the key properties of P91 and P92 steels is their resistance to creep deformation. Creep refers to the time-dependent deformation that occurs under prolonged exposure to high temperatures. These steels are designed to maintain their mechanical properties and dimensional stability even under long-term exposure to elevated temperatures.
- Oxidation resistance: P91 and P92 steels have good resistance to oxidation at high temperatures. The chromium content in the steels forms a protective oxide layer that prevents further oxidation and helps in maintaining the integrity of the material.
- Weldability: P91 and P92 steels are weldable, although special considerations need to be taken due to their high carbon and alloy content. Proper preheating, interpass temperature control, and post-weld heat treatment are essential to avoid issues such as cracking and loss of mechanical properties.
- Applications: P91 and P92 steels are commonly used in the construction of high-temperature components in power plants, such as boiler tubes, headers, and steam piping. They are also utilized in petrochemical and refining industries for applications involving high-temperature and high-pressure environments.
It’s worth noting that while P91 and P92 steels have excellent properties for high-temperature applications, proper design, fabrication, and maintenance procedures are crucial to ensure their optimal performance and longevity.
ETD Press Release on Power Technology:
“p91/p92 Steel Inspection and Life assessment
ETD Consulting has started a new two-year group-sponsored project (GSP), which is open for sponsorship and participation.
With a number of cracking and failure incidents in P91 components worldwide, some occurring early in service, inspection and early stage damage detection and safe remaining life assessments of components made from high Cr martensitic steels has been of particular concern to plant operators, service providers and plant manufacturers. The service damage in these steels and its implications on the safe remaining life is very different from that in the traditional low-alloy steels and needs special tools and methodologies to rectify.”
Development of P91-P92 inspection and life assessment tools
“It is envisaged that the inspection, monitoring and reliable life assessments of P91 and P92 steels, the use of which is now becoming common in all new power plants and as replacement components in older plants, will be a dominant issue in the operation and maintenance of all power plants. Therefore, this initiative should be of particular interest to all utilities, plant operators and service providers.”
The project is open to new sponsors. Please contact ETD if you are interested in joining