Question

(b) A 2 4 CoMo alloy steel pipe with a radius of 20 mm and a wall thickness of 4 mm contains hot fluid under constant pressure (10 MPa) and constant temperature (700°C). The stress (o) on the pipe wall is given by the equation: σ Prit, where P is pressure, r is radius and t is wall thickness. The creep constants for the alloy steel are in the following table. (i)What is the creep rate of the pipe? (ii)If the radius of the pipe is 20 mm at the onset of the second stage by how much will it extend in mar the first year? mar (iii)Which creep mechanism is dominant? Justify your answer. (iv)Describe how this mechanism leads to rupture using detailed and illustrated sketches. (v)Suggest and explain one approach to improve the resistance of this material to creep. (2 marks) (5 marks) (2 marks) Creep Constants Reference stain rate, Value 3.48 X101° s Reference stress, σο 169 MPa Stress exponent, n Activation energy for creep, Qc 7.5 280 kJ.mol 8.31 J.moll.K Gas Constant, R Table Q4. Creep constants for a 2 4 CoMo alloy steel.

Answer 1

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