wiche metal materials is suitable for fabrication a tank at -70 celcious degree and 16 bar pressure?

Answer 1

You will have to give more information for a definitive answer. There are two aspects to consider -
1. Mechanical strength - relating to the size of the vessle and hence its classification in the ASME design codes as being a pressure vessle.
2. Metallurgy - especially with regard to corrosion resistence including for example metal embrittlement and blistering through exposure to hydrogen.

Industrially these conditions (70- deg C and 16 bar) are mild conditions and normally (unless for corrosive service) one would use Carbon Steel in such an application with a 3 mm or so corrosion allowance (depending on the service required)

Answer 2

Steel can lose its ductility at -70C, so this needs to be factored into the stress calcuations. It can become brittle and the critical flaw size becomes very small.

Non-ferrous materials don't lose their ductility at low temperature like steel, so aluminum or titanium can be considered.

The final choice depends on other factors like the chemical environment, weight requirements, and cost.

I think the point of the question is that steel can become brittle at low temperatures, and you need to know and test for the "Nil Ductility Temperature" (NDT).

Answer 3

Titanium

Answer 4

Watch out that the pressure vessel contents (liquid gases?) do not drop in temperature in any event that causes loss of pressure.