Steel Tube Handbook - 2018

4 Overview of the main characteristics of steel tubes L e This chapter is a general description of the characteristics that serve as the basis for the description of individual par- ticular types and groups of steel tubes. These are: • Tube dimensions • Steel for tubes - The definition and distribution of steel - System of marking steel for the tubes according to EN • Technical delivery conditions (TDC) for tubes (excluding testing) • Test of tubes - Types of testing - Types of inspection documents - Individual tests The tube dimensions The tube dimensions are fundamental characteristics of tu- bes. For industrial purposes and general use the tubes are manufactured with diameters ranging from tenths of a mil- limeter to the diameter of a few meters. Tube size must be given in such a way that it is fully de- fining the tube in this regard. For tubes of circular cross section, besides the length, three main dimensions emer- ge: outside diameter, inside diameter and wall thickness. For circular tubes two of the values are given. According to tube type the relevant dimensional tolerances are assigned to dimensions. Dimensions of individual tubes are not created randomly, but are arranged according to the dimensional array of a specific system. The tube dimensions are in mm, in the USA and some other countries are given in inches (English „in- ches“, German „Zoll“). In this case, the tubes are also classi- fied into two groups - „Tube“ are tubes for mechanical usa- ge and for energy facilities and in inches is given the actual outside diameter.„Tubes“ are tubes used in pipelines for dif- ferent types of media. Tubes size is given as nominal tube size, and up to 12 inches is given approximate size (lumino- sity) of the internal diameter of the tube (in more detail in the relevant types of tubes). From dimensions of tubes after conversion to millimeters used in the SI system is created first and preferred array of outside diameters of steel tubes (1st series in EN 10220, DIN 2448, etc..). This does not mean that the tubes in the 2nd and 3 series are not used in practice. Dimensions in series 2 and 3 (for use in Europe are supplemented by the rounded off dimension in mm) are the standards for tube, used in the construction of power facilities and for tubes for me- chanical usage. The group of wall thicknesses has its origin in the inch system, which is used to express the size fractions. Wall thickness in Tubes forms the array of „Schedule“ (40, 60, 80, 120, ...), connected in some dimensions to the weight category (STD, XS, XXS). These values are converted to mil- limeters and form a group wall thickness. (Note: size - the value of Schedule e.g. 40 is not constant, but depends on the outside diameter of the tube). For Tube wall thickness the values are derived from the„scales“ BWG, SWG, possibly others. After conversion to mm, these values become part of tube wall thickness group for steel tubes. For precision steel tubes used in Europe and in countries using SI units we established dimensional series with rounded off dimensions of the outside diameters and wall thicknesses. Ovality, eccentricity Ovality (O) (non-circularity) is defined as the difference between the largest and smallest outer diameter at a gi- ven cross section of the tube. Ovality is allowed under fra- mework of the outside diameter tolerances (EN 13 508). O = D max – D min (absolute value in mm) O = 100.(D max – D min )/D nominal (in%) Eccentricity (E) (eccentricity) is a measure (size) of the dif- ference between the centers of the outer and inner diame- ter. Eccentricity is permitted within the tolerances of wall thickness and is calculated from the thickness of the walls in one cross section: E = (T max –T min )/2 (absolute value in mm) E = (T max –T min )/(T max +T min ).100 (in%) Tolerances (deviation limits) for outside diameter, inside diameter and wall thickness are always valid for only two ordered values. Limits of the third dimension can be arran- ged only for precision tubes. Tube straightness deviation (e) indicates the maximum deviation of the tube from a line joining its two ends, whe- re L is the length of the tube. It is given in percentages per unit length. e / L x 100% Tube weight A theoretical weight (M) is calculated by the formula: M = 0.0246615 x (D - T) x T [kg/m], D,T [mm] M =10, 69 x (D - T) x T [lb/ft]. D,T [in] This applies to carbon steel. For other types of steel, the va- lue multiplied by the coefficient: Type of steel Specific weight Coefficient Carbon 7,85 kg.dm -3 1 Austenitic stainless 7,97 kg.dm -3 1,015 Ferritic and martensitic 7,73 kg.dm -3 0,985 The standards set out the permissible tolerances for tube weight from the theoretical weight. Calculated table weight of pipeline tubes in kg / m (Table 7/Page 44 and Table 20/Page 59) may vary depending on whether in the calculation we used tube wall thickness in mm rounded off to one decimal place (release API 5L Standard until 2004), or to two decimal places (dimensions according to ASME B 36.10M regulation currently in force even for pipeline tubes according to API 5L Standards).