Pipe sizes are not arbitrarily determined and should follow a specific size system. Steel Pipes are sized in millimeters, although some countries use inches (English inch, or German zoll). Therefore, there are two sets of steel tubes - TUBE and PIPE.
TUBE is used in the mechanical or energy industry to describe the outside diameter in dimensions and inches. PIPE is used as a pipeline for different media. The PIPE size is used as the nominal size of the steel pipe. A 12-inch steel pipe can also find an approximate internal diameter.
The Thick Steel Wall series comes from the British metrology unit and uses the score to express the size. The PIPE wall thickness consists of the Schedule series (40, 60, 80, 120) and is connected to the weight series (STD, XS, XXS). These values are converted to millimeters as part of the tube wall thickness series. (Note: Size - the value of Schedule40 is not constant, but depends on the outer diameter of the tube.
For TUBE type wall thickness values use BWG, SWG scale. After conversion to millimeters, these values become part of the thick wall series of steel pipes. Precision steel pipes for use in Europe and in the International System of Units are rounded to approximate outer diameter and wall thickness dimensions.
Steel tube ellipticity
Ellipticity is the difference between the minimum and maximum outer diameter values of a section. The ellipticity must be within the outer diameter tolerance.
Ellipticity = External view maximum value - External view minimum value (mm absolute value) O = ODmax – ODmin (absolute value in mm)
Ellipticity = 100x (outer view maximum - outer diameter minimum) / outer diameter (use %) O = 100. (ODmax – ODmin) / OD (in %)
Steel pipe eccentricity
(Average deviation) is the difference between the intermediate value of the outer diameter and the inner diameter. The eccentricity must be within the thick wall tolerance, and the eccentricity can be calculated in a long cross section:(thick wall maximum - thick wall minimum) / 2 (in millimeters absolute) (WTmax – WTmin) / 2 (absolute value in mm)
(thick wall maximum - thick wall minimum) / ((thick wall maximum + thick wall minimum) x 100 (with %) (WTmax - WTmin) / (WTmax + WTmin).100 (in %).
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