Pipe Fittings, Flanges for Oil, Gas, Electric Power, Shipbuding, Chemical Engineering from WH-STEEL CO., LTD.
Home >> News

How Is The Steel Pipe Size Series Determined?

Jul 10, 2019

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.

Steel Pipes

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 %).


Elbow Packaging Elbow Packaging View More
Mitre Bend with 3LPE Mitre Bend with 3LPE View More
45°Bend with 3LPE 45°Bend with 3LPE View More
30° 4D  Bend 30° 4D Bend View More
  • Tel: +86 157 2731 7311
  • Fax: +86-317-6392671
  • E-mail: sales@whsteelfittings.com
  • Factory Add:

    Zhenggang Industrial Park, Yanshan County, Cangzhou City Hebei Province, China.

  • Tel: +86 157 2731 7311
  • Fax: +86 10 5716 3742
  • E-mail: sales@whsteelfittings.com
  • Office Add:

    No.8013 FuHuaHongYan Building,HongYan South road,Chaoyang District ,Beijing ,P.R.CHINA

Copyright © WH-STEEL Co., Ltd. All Rights Reserved |Sitemap|

Chat Online
kellyzhang200454 WhatsApp Wechat QQ QQ

Middle East International Petroleum Expo

Time: 11-14 NOVEMBER 2019

Booth No: booth 10434, 10th Hall