P11, P22, P9 and P91 Material

The main difference is due to chemical composition. They have more alloying elements in the order you wrote (minimum for P11 and maximum for P91) being Cr the main element added to increase heat and oxidation resistance.

They are used mainly in hot temperature application, higher temperature as alloying increases. One P91 typical application is for main steam piping in power plants.

There are also a new developped P92 grade (a modification of former P91)

All above materials, classified under Low Alloy High Strength Steels are know as Chromium-Moly steels and have in common considerable amount of Chromium ( to avoid oxidation at high temperature and corrosion) and Molybdenum ( to provide grain refining, good creep resistance, and Tensile at high temperature) apart from C, Mn & Si.

They are ment for High temperature service like boiler tubes and used in Thermal and petro chemical units.

P11 has typical chemistry of 1 Cr & 1/2 Mo. Represents ASTM A 387Gr.B, A 182-F2,F11, A 387 -11, A213-T2 & T11, Din steels 15CrMo3, A 335 Gr. P2 - P11 type materials and used for Service Temp. up to 500 ⁰C. or so.

P22 has typical chemistry of 2 1/2 Cr & 1 Mo. Represents ASTM A 387 Gr. D, Din steels like 10CrMo9,10 etc., and used for Service Temp. up to 600 ⁰C. or so

P91 has typical chemistry of 9Cr & 1Mo & Vanadium. Represents SA 213 T91, SA335 P91, SA 336 F91, SA 234 WP01, SA 387 Gr. 01 Cl2, SA 369 FP91 etc. and used for Service Temp. above 700 ⁰C. or so.

The major difference between P9 and 91 is the addition of element Vanadium in P91.

Apart from above we have C -0.5 Moly, 1 Mo - 0.5 Cr, 3Cr, 7Cr, 1Cr-0.5 Mo -0.5V type of materials, used for various applications depending up on the service conditions.

All above are weld-able but, pre-heating - Post heat treatment, the range and cycle depending upon the type of material selected.

All the above details and further information running in to columns are available on most of the web pages.

C Sridhar - AIWT- Chennai- India.

Hi There,

Can these material be used for cool temperature services, e.g. -20 ~ -40 Deg C?

No. They are for use at High temperature service only.

for use at lower Temperature side, say less than 0⁰ C, and say up to -100⁰C the material selection is different and have additional Nickel and (or) Manganese . It will not have Cr and Molybdenum.

Example – A 516 Gr. 70 LT 50 (LT for Low Temperature) up to – 46⁰C (1.60 Mn)

BH39 & 47, BHW27 & 30, ALDUR 45/60 etc. Up to - 50⁰C (1.7 Mn & 0.4 to 0.8 Ni)

ASTM A 203 Up to - 60⁰C (1.7 Mn & 1.0 to 1.1 Ni) or (1.25Mn & 2.0 to 2.75)

A 300, A 353 Up to - 100⁰C (1.25 Mn & 3.0 to 3.75 Ni), like wise.

Similarly, we have Armco Cryonic 5 for use in LNG field and suitable up to-160⁰C,

ASTM A353 /A533 with 9 % Ni for use up to - 196⁰C. etc.

Sridhar.

Thank you for your valued information.

What about the corrosion resistance for those material ?

Which media? steam? acids? concentration? temperature? Any material may perform very well against corrosion in some media and very bad in some other. You should specify a little bit.

Anyway, generally speaking, steel corrosion resistance in aqueous media increases with Cr content, but the behaviour depends on some other parameters (aireation, presence or absece of chlorides, et.)

Generally speaking since all the above high temp. materials have Chromium as alloy they have good corrosion resistance. But may form scaling inside the pipe depending upon the media flowing th' and temperature in service.

Further the pipes may suffer corrosion depending upon service conditions and application areas like Thermal stations, Petrochemical (or) Fertilizer plants. The sulphur, phosphors, CO₂, and other gases released in the atmosphere from the plants mix with moisture, dew at nights and will form sulphuric, phosphoric (or) other acid - rains and fall on the pipe surfaces.

Since pipes are alloyed with Cr. as main element and if they are not properly post heat treated after welding, the weld and HAZ may form certain hard spots. Along with surface defects like Undercuts, arc strikes, they are venerable for attack from these acids and similarly by certain alkalines and likely to corrode in the course of service.

This is one of the reasons for these plants to have compulsory yearly shut downs and most of the pipes, valves etc are fully replaced. This helps to avoid plant break downs during production and it is difficult to pin point the catastrophic losses if the lines leak / crack and production gets disturbed.

Trust above details are useful to you.

Sridhar.

I'm performing a weld repair on a P22 sch 60 to P11 sch 40 butt weld, the crack I'm trying to repair keeps growing, I'm using a 360F rosebud localized preheat, what can I do to stop the crack from growing? Thanks in advance for any help provided.

Sorry, you talk just of preheating, but which welding process? Which filler metal composition?...

Give some more details, please

Kind regards