a. For outer diameters less than 2 3/8 in (60.3 mm), pipe body diameter tolerance +/-0.5 mm. Pipe end +/- 0.5 mm; Out of Roundness tolerance for pipe body is 0.9 mm (0.036 in), pipe end 0.6 mm (0.024 mm).

b. For OD equal or above 2 3/8 in (60.3) to 24 in (610 mm), (diameter tolerance) for pipe body is +/- 0.0075D, pipe end +/- 0.005D but max to +/- 1.6 mm (0.063mm); Roundness tolerance for pipe body ≤ 0.015D, pipe end ≤ 0.01D.
(In case agreed with manufacturer and client, more strictly tolerances could be applied)

c. For wall thickness
Below than 4 mm (0.0157 in), tolerance +0.6 (0.024 mm), -0.5 mm (0.020 in);
For API 5L seamless steel pipe thickness in 4 mm to 10 mm (0.394 in), +0.150t, -0.125t;
For API seamless pipe thickness 10 mm to 25mm (0.984 in), +/-0.125t;
Wall thickness ≥ 25 mm, +3.7mm or +0.1t (if larger) and -3.0 mm (0.120 in) or -0.1t (if larger).
t for thickness;
d. For straightness, max for full length, tolerance maximum 0.15% of length.
e. Straightness, max deviation for pipe end, shall be ≤ 0.3 mm /m.
f. Length +/- 200 mm for general, +/- 25.4 mm for special.

The production method of seamless steel pipe is roughly divided into a cross-rolling method (Mengnesmann method) and an extrusion method. The cross-rolling method is to first pierce the tube with a diagonal roll and then extend it with a rolling mill.

This method has a high production speed, but has high requirements on the processability of the tube blank, and is mainly suitable for the production of carbon steel and low alloy steel tubes. The extrusion method uses a piercing machine to perforate a tube blank or a steel ingot and then extrudes it into a steel tube by an extruder. This method is less efficient than the cross-rolling method and is suitable for producing a high-strength alloy steel tube.

Seamless steel pipe manufacturing process:
①Main production process of hot-rolled seamless steel pipe (main inspection process):
Tube blank preparation and inspection →Tube heating→Perforation→Rolling pipe→Steel pipe reheating→fixed (reduced) diameter→Heat treatment→Finish pipe straightening→Finishing→Inspection(non-destructive, physical and chemical, bench inspection)

②Main production process of cold-rolled (drawn) seamless steel pipe:
Blank preparation → pickling and lubrication → cold rolling (drawing) → heat treatment → straightening → finishing → inspection

Seamless steel pipes are widely used in water and gas pipelines and are also used in petroleum, chemical, boiler, automobile, tractor, aviation, and other fields. According to the use, it can be divided into two types: general-purpose (for water, gas pipelines and structural parts, mechanical parts) and special (for boilers, geological exploration, bearings, acid resistance, etc.).

A structural seamless steel pipe is a pipe with a hollow section and is used as a large amount of conveying fluid, such as pipes for transporting oil, natural gas, gas, water, and certain solid materials. Compared with solid steel such as round steel, the steel pipe has a lighter weight when it has the same bending and torsional strength and is economical section steel.

Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automotive drive shafts, bicycle frames, and steel scaffolding used in construction, such as steel scaffolding, to create ring-shaped parts, which can improve material utilization, simplify manufacturing processes, save materials and processing.