MITTEL has been a provider of high-quality products and parts since
2012 . No matter your industry or problem, our experienced team
will work to provide your company with exactly the solution you
need. Though our inventory is already considered one of the best,
we are always growing, and we are always evolving to meet the
highest standards possible. All of our A335 P91 Type 2 material are
of the highest quality from approved international manufacturers.
As technology continues to advance, we do, too. ASTM A335 P91 Type
2 evolved from EPRI recommended Code Case 2864.
Characteristics of ASTM A335 P91 Type 2
P91 is a chrome moly alloy metal that contains excellent strength
and temperature resistance. It is designed for enhanced creep
strength, making it a creep strength enhanced ferritic (CSEF). This
metal is made by normalizing at 1050 °C, air cooling to 200 °C, and
then tempered through heating to 760 °C. This process is the main
reason behind P91’s creep strength and durability. P91 stands for
the metal’s composition of 9% chrome and 1% molybdenum plus
vanadium. The chrome increases temperature strength and oxidation
resistance. The molybdenum increases the elasticity, resistance to
wear, and high temperature creep strength. More characteristics to
note of ASTM A335 P91 Type 2:
- Non-deteriorating
- Decreased thickness
- Higher creep strength
Applications of ASTM A335 P91 Type 2
MITTEL can meet your ASTM A335 P91 Type 2 requirements when it
comes to fittings,tubing, flanges, valves, and much more. This
metal is made and typically usedfor very high heat situations in
industries such as chemical processing andpower plants.
Some more common uses of ASTM A335 Type 2include
- Power generation
- Gas processing equipment
- Oil services
- Petrochemical plants
- Heaters/reheat lines
- Boilers
Contact our experienced and educated team at U.S. Metals today to
discuss all your P91 needs. We use only high-quality materials to
bring you the best performing products.
About ASTM A335 P91 Pipe
Trade Name: P91
Grade: P91
UNS #: K91560
Pipe: A335/SA335
Forged/Bored Pipe: A369/SA369
Length: Specific or random
A335/SA335 P91 is a ferritic alloy steel that has very high
strength properties, which do not deteriorate with time, and are
creep resistant. It is also called 9 Cr 1 Mo steel, or chrome moly
pipe, based on its composition.
Compared to its predecessors, the T22 or P22 grade, grade P91
exhibits high strength, enduring temperatures up to 600 °C. The
oxidation temperature limits are also higher allowing elements to
be engineered with less thickness. This contributes to an almost 10
times higher thermal fatigue life and allows engineers to increase
the operating temperature to a higher level, increasing efficiency.
P91 typically allows a wall thickness reduction by at least a
2-to-1 ratio. A wall that is thinner creates lighter hanger loads,
less welding time and uses less filler metal.
These advantages are enabled by this steel’s high amount of
chromium. Grade 91 contains 9% chromium and 1% molybdenum compared
to 2.5% chromium in the next best P22 grade
P91 Pipe Chemical Requirements
- Carbon - 0.08% - 0.12%
- Manganese - 0.30% - 0.60%
- Phosphorus, max - 0.020%
- Sulfur, max - 0.010%
- Silicon, max – 0.20% - 0.50%
- Chromium - 8.00% - 9.50%
- Molybdenum - 0.85% - 1.05%
- Vanadium: 0.18% - 0.25%
- Nitrogen: 0.030% - 0.070%
- Nickel: 0.40% Max
- Aluminum: 0.02% Max
- Columbium: 0.06% - 0.10%
- Titanium: 0.01% Max
- Zirconium: 0.01% Max
Chromium, or chrome, improves high-temperature strength and
increases oxidation resistance. It is virtually irreplaceable in
resisting oxidation at elevated temperatures. Chrome also raises
the tensile, yield and hardness at room temperatures.
Molybdenum increases the strength, elastic limit, resistance to
wear, impact qualities and hardenability. It increases the
resistance to softening, restrains grain growth and makes chromium
steel less susceptible to embrittlement. Moly is also the most
effective additive for increasing high temperature creep strength,
or creep resistance. It also enhances the corrosion resistance of
steel and inhibits pitting.
Also present are smaller quantities of nickel and manganese which
increase the hardenability of the steel.
The addition of Vanadium (V) and Columbium/Niobium (Cb/Nb) as well
as the control of Nitrogen (N) greatly Improves Creep Strength.
More important than the alloying elements is the formation of this
alloy steel. The steel is formed by normalizing at 1050 °C, then
air cooling down to 200 °C. It is then tempered by heating to 760
°C. The temperatures and cooling rates produce the microstructure
that results in the high creep strength properties.
P91 Pipe Specifications
- Tensile strength, min, PSI, (MPa) – 85,000 (585)
- Yield Strength, min, (MPa) – 60,000 (415)
P91 Pipe Applications
A335/SA335 P91 is suitable for bending, flanging (vanstoning), and
similar forming operations and for fusion welding. P91 is most
commonly used in the power industry and petrochemical plants where
fluids and gases are transported at extremely high temperatures and
pressures.
P91’s strength and high temperature endurance makes it ideally
suitable for plants that operate on a cyclic basis - like combined
cycle plants. Also, the reduction in thickness suits HRSG
designers, in an HRSG the temperature head is limited and locating
the coils in the heat transfer path is very critical.
P91 is the correct grade for:
P91 Welding Procedure
When welding P91, preheating, maintaining inter-pass temperatures
and post-weld treatment procedures are essential to maintain the
P91 grade. Welding has an important effect on the microstructure
and failure to follow the procedures will result in catastrophic
failures.
For thick-walled pipes, the use of a modern induction heating
system – where the coils do not heat up – is the ideal method. This
gives better control, and uniform heating between the inner and
outer diameters. Induction heating is ideal for maintaining the
inter-pass temperatures and carry out the welding. This is also a
more worker-friendly heating process and is ideal for complex
shapes like weldolets and tees.
The composition of the welding electrodes used should always be in
line with the parent material. The nickel and manganese content of
P91, though in smaller percentages, has profound effects on the
critical temperatures, which decides the heat treatment
temperatures and the cooling rates.
Steel that has not been heat-treated has a great affinity to
hydrogen which can cause stress corrosion cracking. Pre-heating
must be done properly to remove any moisture. In addition, the
post-weld heat treatment must be done as quickly as possible to
avoid any contact with moisture from condensation, rainfall, etc.
Be sure all joints are post-weld heat treated prior to hydro test.
