Schedule of pipe

All of your questions shall be answered through solving the following (repeated) example for determination of pipe wall thickness (except compressibility ?).

The example and a lot of comments were derived through [CR4] Specifying Seamless Pipe for a Steam Line. Also refer to [CR4] Maximum Wall Thickness for Seamless Pipe for other details.

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The pipe wall thickness is determined from the applicable formula of the pertinent ASME B31.1, Power Piping (not B31.3, Process Piping).

Given : Code : ASME B31.1

Design Pressure (P) : 13 bar (188.5 psi), [oper. press. 10 bar (145 psi)]

Design Temperature : 180 ^oC (356 ^oF), [oper. temp. 150 ^oC (302 ^oF)]

Material : ASTM A106 Grade B, Seamless

Nominal Pipe Size : 3 inch

Find : Minimum Theoretical Wall Thickness, t_m & Minimum Nominal Wall Thickness, t

Data : t_m = P D_o / (2 S + 2y P) + C (ASME Code B31.1)

Corrosion Allowance, C = 3 mm (0.11811 in.)

Factor, y = 0.4 (for carbon steel) [ASME Code B31.1, Table 104.1.2(A)]

Joint efficiency, E = 1.0 (for seamless pipe E=1)

Pipe Outside Diameter, D_o = 3.5 inch

Allowable Tensile strength, S @ 356 ^oF=15000 psi (ASME B31.1,Table A-1)

Wall Thickness Tolerance = 12.5% (ASME B36.10 & ASTM A106)

Solution : By substitution into equation,

t_m = P Do / (2 S + 2y P) + C

= (188.5 psi)(3.5 inch)/(2*15000 psi +2*0.4*188.5 psi) + 0.11811 inch

= 0.14 inch (3.6 mm)

Which is the theoretical minimum for wall thickness without allowing for wall thickness tolerance.

Thickness adjusted for wall thickness tolerance, t = t_m / (100%-12.5%)

= 0.14 inch/(1-0.125)=0.14/0.875= 0.16 inch (4.06 mm)

The next greater commercial wall thickness is found from ASME B36.10 to be 0.216 inch (5.49 mm) which corresponds to 3" Sch. 40.

In other words 0.216 inch nominal pipe wall thickness is the commercial wall which, when reduced by the full tolerance of 12.5%, satisfies the code formula for t_m

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