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National Standard Enterprise Standard ComparisonResultsWelded Steel Pipe for Transportation of Low Pressure FluidWelded PipeOutside Diameter of Steel PipeOutside Diameter of Steel Pipe, Tolerance of Outside DiameterBetter than National Standards Outside Diameter D/mm Tolerance of Pipe Outside Diameter Tolerance of Pipe End Outside Diameter/mm Outside Diameter D 8" ±0.60mm D≤48.3 ±0.5mm 5"-6" ±0.50mm 48.3<D≤168.3 ±1.0% 4" ±0.40mm 168.3<D≤508 ±0.75% +2.4 -0.8 3"-2½” ±0.30mm D>508 ±1.0% +3.0 -0.8 D≤2” ±0.20mm Tolerance of Wall Thickness ±12.5% Wall Thickness S 1.8-5.75mm 5% Length Usual Length Tolerance Length Better than National Standards D≤2” +5-0 4M-12M +20-0 2½” ≤D≤4” +10-5 Multiple length: 5-10mm tolerance for each Multiple length +20-0 5” ≤D +15-0 +20-0 Bending ≤168.3mm Straight for ordinary use or negotiate the bending Bending ≤1.5% Better than National Standards >168.3mm Smaller than 0.2% of full length of steel pipe Pipe End The two end faces of steel pipe should bu vertical with axes of the steel pipe. No burr in the incising Pipe End The two end faces of steel pipe should be vertical with axes of the steel pipe. No burr in the incising Equal to International Standards ≥168.3mm Cutting tilt: no more than 5mm ≥168.3mm Cutting tilt: no more than 5mm Chemical Composition Execute according to GB/T222, GB/T223 and GB/T4336 Chemical Composition Execute according to GB/T222, GB/T223, GB/T699, GB/T700, GB/T1591 and GB/T4336 Better than International Standards Mechanical Properties Execute according to GB/T228,GB/T6397, GB/T244 and GB/T246 Mechanical Properties Execute according to GB/T228, GB/T6397, GB/T244 and GB/T246 Equal to International Standards Surface Quality Of Steel Pipe Internal and external surface of pipe should bu slick. Folding crack, delamination and lap weld are not permitted. Other defects that no more than the negative deviance of wall thickness are permitted. Internal burr is allowed to exist. Steel pipe with>100mm, could be repaired for its defects and carry out water pressure experiment. Surface Quality Of Steel Pipe Steel Pipe should not have defects such as crack, scar, folding, delimination, and lap weid etc. Pull line, scoring, weid seam dislocation, scuffing not larger than the negative deviance of wall thickness and the trace of eliminating skin of ferric oxide and burr are allowed. Internal burr is allowed to exist. Better than International Standards