6 Working_Pressure

The working pressure of a component is the Maximum Allowable Working Pressure (MAWP) for the metal working temperature (design temperature). The MAWP permitted for different components as per The Indian Boiler Regulations, 1950 – (IBR - with amendments) – are given below:

IBR Formula for the shell of Headers and Drums (IBR-270, 1950)

WP =  2 f E(T –C)
_____________
(D +T – C)
Hence,
T =   WP x D
(2 f E – WP)
Where,
T = minimum required thickness, mm
WP = working pressure, kg / sq mm (g)
D = drum inside diameter, mm
f = drum metal allowable stress, kg / sq mm
p = tube hole longitudinal pitch, mm
d = tube hole diameter, mm
C = 0.03 inch = 0.762 mm
E = (p-d) / p = longitudinal ligament efficiency

IBR Formula for straight Tubes (IBR-338,1950)
WP =               2 f E(T – C)
WP x D + C
Hence,
WP =                WP x D + C
(2 f +WP)
Where,
T = minimum required thickness, mm
WP = working pressure, kg / sq mm (g)
D = tube outside diameter, mm
f = tube metal allowable stress, kg / sq mm
C = 0.75 mm when WP = 70 kg / sq cm (g) and lower
= 0.0 mm when WP = above 70 kg / sq cm (g)

IBR Formula for straight Pipes (IBR-350,1950)
T =    WP x D + C
(2 f E – WP)
Where,
T = minimum required thickness, mm
WP = working pressure, kg / sq mm (g)
D = tube outside diameter, mm
f = tube metal allowable stress, kg / sq mm
E = joint efficiency
C =0.75 mm