Re: PIPE THICKNESS CALC (formulas)

From: <elie>
Date: Sat Sep 17 2005 - 09:29:00 EDT

For B31.3
To determine allowable internal working pressure for straight sections of pipe in accordance with ANSI B31.3, “Code for Pressure Piping, Petroleum Refinery Piping”, use the following:

t(m) = t+c
t=Pi * do / [2(S’*E’+Pi*Y’)]

where:
tm = minimum required thickness, satisfying equirements for pressure, and mechanical, corrosion, and erosion allowances, inches. (The minimum thickness for the pipe selected, considering manufacturer’s minus tolerance,
shall not be less than tm).
t = pressure design thickness, in.
c = the sum of the mechanical allowances (thread depth and groove depth), corrosion, and erosion allowances, in.
Pi = internal design pressure, psig.
do = outside diameter of pipe, in.
S&#61602;&#61472;= allowable stresses, psi. E&#61602;&#61472;= longitudinal weld joint factor: Seamless = 1.000, ERW = 0.85
Y"= coefficient having values for ferritic steels as follows: 0.4 up to and including 900°F, where: tm = minimum required thickness, satisfying equirements for pressure, and mechanical, corrosion, and erosion allowances, inches. (The minimum thickness for the pipe selected, considering manufacturer’s minus tolerance,
shall not be less than tm).
t = pressure design thickness, in.
c = the sum of the mechanical allowances (thread depth and groove depth), corrosion, and erosion allowances, in.

Pi = internal design pressure, psig.
do = outside diameter of pipe, in.
S" = allowable stresses, psi. (from B31.3, Appendix A,

Tables A-1, A-1B)
E" = longitudinal weld joint factor:
Seamless = 1.000, ERW = 0.85
Y" = coefficient having values for ferritic steels as follows: 0.4 up to and including 900°F 0.5 for 950°F, 0.7 for 1,000°F and above, 0.5 for 950°F, 0.7 for 1,000°F and above

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For B31.8

To determine allowable internal working pressures for piping outside of refineries and other processing facilities in accordance with ANSI B31.8-1992, “Code of Pressure Piping, Gas Transmission and Distribution Piping,” use the following:

Pi=2*S”*t*F”*E”*T”/do

Where:
Pi = Design pressure, psig
S"&#61472;= Specified minimum yield strength, psi do = Nominal outside diameter, in.
t = Nominal wall thickness, in.
F"&#61472;= Construction type design factor, Table 841.114A and Par. 840.2 (see note)Complete details are covered in Par. 841.
E"= Longitudinal joint factor, Table 841.115A Normally a factor of 1.0 is used for seamless and welded pipe except for the following:
Fusion Welded A 134 and A 139 E"=0.80
Spiral Welded A 211 E"=0.80
Furnace Butt Welded ASTM-A53, API-5L E"=0.60 T"&#61472;= Temperature derating factor, Table 841.116A
Temp, °F 250 or less Factor T"=1.000

Temp = 300 T"= 0.967
Temp = 350 T"= 0.933
Temp = 400 T"= 0.900
Temp = 450 T"= 0.867

For intermediate temperatures, interpolate for derating factor.
Note: Factor reflecting location of line, proximity to roads, public or private land, etc.

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