Materials Engineering

Materials Engineering
Name
Institution

Materials Engineering
1. An 212A42 steel is to be used to manufacture pressure vessel capable of storing
superheated steam at a temperature of 700֯ C and at a stress of 30MPa. Using the attached
chart, determine the safe working life of the vessel. Some approximation will be
necessary.
To establish if there is material failure in a pressure vessel, the common methodologies used
include complete scientific methods that utilize a simulation of numerical figures in order to
establish any causes of failure of the pressure vessel such as the use of finite element analysis or
to utilize the s-N curve to derive the service life of the pressure vessel. Typically, the pressure
vessel undergoes cyclic loading that causes cracks and fatigue as is depicted below.
The parameters required for the characterization of the cyclic loading conditions in this pressure
vessel are as follows.
The stress range of the cycle given by:

∆ σ=σmax −σmin
For this case:
∆ σ=30−−30=60 MPa
Stress amplitude of the cycles given by:
σ a= 1
2 (σmax −σmin )
σ a= 1
2 ( 30−−30 )=30 Mpa
Mean stress of the cycles
σ m= 1
2 (σmax + σmin)
σ m= 1
2 ( 30 ±30 ) =0
Load ratio of the cycles
R= σ min
σ max
R=−30
30 =−1
This represents a fully reversed loading whose s-N curve is represented in the following
illustration

For the case of this pressure vessel,
t= 700֯C = 973K
σ= 30MPa
1 2 3 4 5 6 7 8
0
5
10
15
20
25
30
35
s-N curve for the pressure vessel
Cycles to failure (Nf) power of 10
Stress amplitude (σa)