ASTM A312 Pipe Sizes and Dimensions
ASTM A312 Pipe Size is based on the American National Standard for stainless steel pipe (ANSI B36.19). ASTM A312 covers sizes ranging from 1/8" to 30" and wall thicknesses from STD to XXS. It also includes standard dimensions for welded and seamless pipes, which are important for easy interchangeability and compatibility.
| NPS Designator | Outside Diameter | Nominal Wall Thickness | ||||||||
| Schedule 5SA | Schedule 10SA | Schedule 40S | Schedule 80S | |||||||
| in. | mm | in. | mm | in. | mm | in. | mm | in. | mm | |
| 1/8 | 0.405 | 10.29 | … | … | 0.049 | 1.24 | 0.068 | 1.73 | 0.095 | 2.41 |
| 1/4 | 0.540 | 13.72 | … | … | 0.065 | 1.65 | 0.088 | 2.24 | 0.119 | 3.02 |
| 3/8 | 0.675 | 17.15 | … | … | 0.065 | 1.65 | 0.091 | 2.31 | 0.126 | 3.20 |
| 1/2 | 0.840 | 21.34 | 0.065 | 1.65 | 0.083 | 2.11 | 0.109 | 2.77 | 0.147 | 3.73 |
| 3/4 | 1.050 | 26.67 | 0.065 | 1.65 | 0.083 | 2.11 | 0.113 | 2.87 | 0.514 | 3.91 |
| 1 | 1.315 | 33.40 | 0.065 | 1.65 | 0.109 | 2.77 | 0.133 | 3.38 | 0.179 | 4.55 |
| 1 1/4 | 1.660 | 42.16 | 0.065 | 1.65 | 0.109 | 2.77 | 0.140 | 3.56 | 0.191 | 4.85 |
| 1 1/2 | 1.900 | 48.26 | 0.065 | 1.65 | 0.109 | 2.77 | 0.145 | 3.68 | 0.200 | 5.08 |
| 2 | 2.375 | 60.33 | 0.065 | 1.65 | 0.109 | 2.77 | 0.154 | 3.91 | 0.218 | 5.54 |
| 2 1/2 | 2.875 | 73.03 | 0.083 | 2.11 | 0.120 | 3.05 | 0.203 | 5.16 | 0.276 | 7.01 |
| 3 | 3.500 | 88.90 | 0.083 | 2.11 | 0.120 | 3.05 | 0.216 | 5.49 | 0.300 | 7.62 |
| 3 1/2 | 4.000 | 101.60 | 0.083 | 2.11 | 0.120 | 3.05 | 0.226 | 5.74 | 0.318 | 8.08 |
| 4 | 4.500 | 114.30 | 0.083 | 2.11 | 0.120 | 3.05 | 0.237 | 6.02 | 0.337 | 8.56 |
| 5 | 5.563 | 141.30 | 0.109 | 2.77 | 0.134 | 3.40 | 0.258 | 6.55 | 0.375 | 9.52 |
| 6 | 6.625 | 168.28 | 0.109 | 2.77 | 0.134 | 3.40 | 0.280 | 7.11 | 0.432 | 10.97 |
| 8 | 8.625 | 219.08 | 0.109 | 2.77 | 0.148 | 3.76 | 0.322 | 8.18 | 0.500 | 12.70 |
| 10 | 10.750 | 273.05 | 0.134 | 3.40 | 0.165 | 4.19 | 0.365 | 9.27 | 0.500B | 12.70B |
| 12 | 12.750 | 323.85 | 0.156 | 3.96 | 0.180 | 4.57 | 0.375B | 9.52B | 0.500B | 12.70B |
| 14 | 14.000 | 355.60 | 0.156 | 3.96 | 0.188B | 4.78B | … | … | … | … |
| 16 | 16.000 | 406.40 | 0.165 | 4.19 | 0.188B | 4.78B | … | … | … | … |
| 18 | 18.000 | 457.20 | 0.165 | 4.19 | 0.188B | 4.78B | … | … | … | … |
| 20 | 20.000 | 508.00 | 0.188 | 4.78 | 0.218B | 5.54B | … | … | … | … |
| 22 | 22.000 | 558.80 | 0.188 | 4.78 | 0.218B | 5.54B | … | … | … | … |
| 24 | 24.000 | 609.60 | 0.218 | 5.54 | 0.250 | 6.35 | … | … | … | … |
| 30 | 30.000 | 762.00 | 0.250 | 6.35 | 0.312 | 7.92 | … | … | … | … |
ASTM A312 Stainless Steel Pipe Permitted Variations in Wall Thickness
ASTM A312 and ASME SA312 provide regulations on the standard sizes and tolerances of seamless and welded stainless steel pipes for high-temperature and general corrosive services.
In addition to the implicit limitation of wall thickness or seamless pipe imposed by the limitation on weight in specification A 999/A 999M. The wall thickness for seamless and welded pipe at any point shall be within the tolerances specified in the following Table, except that for welded pipe the weld area shall not be limited by the "Over" tolerance. The wall thickness and outside diameter for inspection for compliance with this requirement for pipe ordered by NPS and schedule number is shown in ANSI B36.19.
| NPS Designator | Tolerance, % from Nominal | |
| Over | Under | |
| 1/8 to 21/2 incl., all t/D ratios | 20.0 | 12.5 |
| 3 to 18 incl., t/D up to 5 % incl. | 22.5 | 12.5 |
| 3 to 18 incl., t/D > 5 % | 15.0 | 12.5 |
| 20 and larger, welded, all t/D ratios | 17.5 | 12.5 |
| 20 and larger, seamless, t/D up to 5 % incl. | 22.5 | 12.5 |
| 20 and larger, seamless, t/D > 5 % | 15.0 | 12.5 |
t = Nominal Wall Thickness
D = Ordered Outside Diameter
Mechanical & Hydrostatic Testing Requirements
To confirm that your specified pipelines conform to geometric tolerances and can withstand severe service stresses, ASTM A312 mandates strict inspection protocols:
Hydrostatic Testing: Each pipe length is subjected to a comprehensive internal hydrostatic test to guarantee structural integrity unless a nondestructive electrical test is substituted by the buyer.
Nondestructive Evaluation (NDE): Welded and seamless configurations frequently undergo ultrasonic or eddy-current testing to check for micro-voids or wall thinning.
Mechanical Verification: Flattening, flaring, and transverse tension test samples are systematically drawn from finished production runs to confirm optimal ductility and yield strength.
