Pipe Wall Thickness Calculation as per Code ASME B31.3:
Pipe wall thickness calculation will be done per ASME B31.3 Clause 304.1.2 (3a), on account of internal pressure of pipe with below method.
Basic Equations used for thickness calculation are,
t m = t + c and further t is calculated as per below,
PD t = ---------------- 2 (SEW + PY)
Let’s see what does it mean all terminology used in above equation.
t m Minimum required thickness in “mm”, including mechanical, corrosion, and erosion allowances.
c = Corrosion allowance in “mm”. This is based on project specific requirements or stated in material selection report of project. It may be 0mm, 3mm, 6mm or project specific requirements.
t = is pressure design thickness in “mm”, as calculated in accordance with para. 304.1.2 for internal pressure or as determined in accordance with para. 304.1.3 for external pressure. This is calculated thickness.
P = internal design gage pressure in psi (g) at design temperature of 82 0C.
How can found class pressure or internal gauge pressure?
This design gauge pressure we can get it from line list or from designated piping class. In shell piping classes you can get design pressure with interpolation method as shown below.
Interpolation for intermediate design pressure calculation.
Insert temperature 82 in between 75 & 100.
So , X = 18.204
So, Design Temperature = 82 co ………………… (82 * 1.8) + 32 = 179.6 F o
P = 18.204 bar (g) ………………………………18.204 * 14.50377377 = 264.0247 psi (g)
D = Pipe outside diameter in “mm” as per ASME B36.10M.
S = Allowable Stress value for material from ASME B31.3 Table A-1 or Table A-1M. However to check allowable stress values, we should know the material of construction of the pipe. For e.g. if we are doing thickness calculation for carbon steel pipe with ASTM A106B pipe. We should check A106B material in Table A-1 of ASME B31.3.
Since above stress is given in ksi unit, convert it to psi(g) as below,
For corresponding temperature of 82 0 C, S = 20……….20 x 1000 = 20000 psi.
E = Quality factor from ASME B31.3 Table A-1A or Table A-1B. Since for e.g. for ASTM A106B pipe material as per table A-1B E factor is 1.00.
W = Weld joint strength reduction factor in accordance with ASME B 31.3 para. 302.3.5(e).
Hence as per table 302.3.5 W = 1.0 for carbon steel.
Y = Coefficient from ASME B31.3 Table 304.1.1.
Hence as per table 304.1.1, Y = 0.4
In a summary we know all parameters used in equation. Hence final Calculation of thickness is as below,
In accordance with para. ASME B31.3, 304.1.2(a), t must be less than D/6 for eq. (3a).
i.e. < D/6 = 150/6 = 25. Since calculated thickness is 8.118 is less than 25, ASME B31.3 eq. (3a) is applicable without special consideration of factors listed in para. 304.1.2(b) of 31.3.
Now select a pipe schedule of adequate thickness.
For calculated thickness of tm = 8.118 mm, which is including mill tolerance on 12.5%, select appropriate schedule close to available schedule listed from ASME B36.10M table 1.
Hence final thickness calculated in 10.97 as per ASME B 36.10 with Schedule 80.
