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Note 5 tolerances of steel pipe

Take seamless steel pipe as an example, there are 5 tolerances that affect quality. Noting this, you will get better pipe.
As ASTM A106 and ASTM A530 Standard:

OD tolerance

For standard pipe, except as provided for thin-wall pipe, the tolerances of diameter shall be in accordance with the following table:
For pipe over 10 inch as special OD tolerance pipe, the OD shall vary within +1% /-1%.
NPS/ DN/ OD Permissible Variations in Outside Diameter
Over Under
in. mm in. mm
NPS 1/8 to 1½, incl
DN 6 to 40
OD 10.3 to 48.3, mm
1/64 0.4 1/64 0.4
Over 1½ to 4, incl
DN 40 to 100
OD 48.3 to 114.3, mm
1/32 0.8 1/32 0.8
Over 4 to 8, incl
DN 100 to 200
OD 114.3 to 219.1, mm
1/16 1.6 1/32 0.8
Over 8 to 18, incl
DN 200 to 450
OD 219.1 to 457, mm
3/32 2.4 1/32 0.8
Over 18 to 26, incl
DN 450 to 650
OD 457 to 660, mm
1/8 3.2 1/32 0.8

Thickness tolerance

The wall thickness at any point shall be within the below tolerance table.
NPS/ DN/ OD Tolerance, % from Nominal
Over Under
NPS 1/8 to 2½, incl, all t/D ratios
DN 6 to 65
OD 10.3 to 73.0, mm
20.0 12.5
NPS 3 to 18, incl, t/D up to 5%
DN 80 to 450
OD 88.9 to 457, mm
22.5 12.5
NPS 3 to 18, incl, t/D > 5%
DN 80 to 450
OD 88.9 to 457, mm
15.0 12.5
NPS 20 and larger, incl, welded, all t/D ratios
DN 500
OD 508
17.5 12.5
NPS 20 and larger, incl, seamless, t/D up to 5%
DN 500
OD 508
22.5 12.5
NPS 20 and larger, incl, seamless, t/D > 5%
DN 500
OD 508
15.0 12.5

Length tolerance

For Seamless and Welded pipe, if definite cut lengths are ordered, the length shall vary within -0mm / +6mm.

Weight tolerance

For pipe NPS 12 (DN300, 323.8mm) and under, the weight shall vary within -3.5% / +10%.
For pipe over NPS 12 (DN300, 323.8mm), the weight shall vary within -5% / +10%.
Pipe of NPS 4 (DN100, 114.3mm) and smaller may be weighed in convenient lots; pipe in sizes larger than NPS 4 shall be weighed separately.

Quantity tolerance

Normally mills take -10% to +10% tolerance, but TPMC keeps ±3% variation.