The designer is responsible for the proper specification of the piping, and using recommendations from the internet might be considered a high risk proposition.

Having said that, the design temperature is above the max permitted for carbon steel, and low alloys such as P11 are marginally acceptable if corrosion and erosion were not an issue. Except that they are an issue in this case, depending on what the slurry contains.

The design conditions you listed suggest a supercritical oxidation process is being planned. I think you will need to focus on corrosion, espescially if the water in the slurry has remnant oxygen in it. It is remotely possible that the corrosion could be worsened by surface reactions with the oxygen and the iron scale on the pipe walls; something unusual can happen at these pressures and temperatures.

"Whom the gods would destroy, they first make mad "

And since it is a slurry erosion will likely also be factor.
The materials that are allowed for construction at that temp and have high strength is a rather short list.
And expensive. And not easy to work with.
Talk to your fabricator and see what options they bring forward.
There are some high alloy steels that might be suitable.
Get out your code books and do some research.

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P.E. Metallurgy, Plymouth Tube

Thanks for reply "Davefitz" and "Edstainless", Erosion is also an issue but it's not in top priority, Top one is need to find out material which withstand against such pressure & temperature. I got no. of suggestion from different designer but that vary from SUPER DUPLEX 2507 to SS 310/310S & SS 304. With some options in hand, I can choose material which has higher anti-corrosion property.

Some grade can bear up to 800 Celsius / 200 bar pressure alone but both high temp. & high pressure is present ..material strength seems degrade drastically, Can anyone provide me Pressure/Temperature chart of different material grade.?

Thanks in advance.

First, you need to have a piping design code to work with - ASME B31.1 or B31.3.
Second, at this design temperature duplex stainless steel is not recommended.
Third, if you select several austenitic stainless steels like 304 or 316 or need to upgrade to Ni-base, the piping code will provide allowable stress values for design and here is where you calculate a minimum design wall thickness for piping. There are no pressure temperature charts for piping systems, like for valves or fittings.

Thanks a lot metengr, I will get back after study of ASME B31.1 or B31.3.