Steel Tube Handbook - 2018

52 Tubes with internal ribs Symbol Parameter Range [mm] [inch] D Outside diameter 18–72 .750–3.000 T Tube wall thickness 1–6,5 .047–.250 Number of ribs 6–8 h Rib height 0,3–1,0 .016–.047 f Rib width at the top (cross section) 3–8 .125–.313 ß Rib side angle 30° r Rib radius 0,1–0,15 .004–.006 a Rib pitch angle 25°–35° Rib pitch length (360°) depending on D Distance of rib centers in the longitudinal direction upon agreement s Rib width at the top (longitudinal section) upon agreement Width of the distance between ribs at the top (longitudinal section) upon agreement Inside tube circumference upon agreement Transversal tube diameter upon agreement Tube weight kg/m lb/ft Tube length upon agreement Parameters of tubes with internal ribs Table 17 Today, there is still prevailing use of tubes with smooth surface for the purposes of construction as well as reconstruction of energy type facilities even despite that fact that tubes with surface structure (tubes with interior ribbing) positively influence performance of energy type facilities. Tubes with interior ribbing are intended for high-performance steam generators, for high-pressure boilers and are also used in the area of burners and other equipments. Interior ribs cause separation of steam and liquid as a result of centrifugal power, whereby the fluid phase (water) is forced to the tube wall, where it is stored longer as a water film. Using this method prevents occurrence of boiling on the interior tube wall which prevents exchange of heat and may also be the cause of occurrence of critical zones of commencing distortion of steel tube. Admissible share of water steam while retaining the heat flow and using ribbed tubes thus increases in the interval of 20 – 40 %, when using smooth surface tubes to 70 – 90 %. That phenomenon results in increasing the contact surface area between the liquid part and tube wall, which brings about the following benefits: • Improves the level of heat transfer even with a higher share of steam, • A very good level of heat transfer is retained also at lower medium flow, • Temperature of tube walls is reduced and so is the risk of distortion of tubes, • It also prepares the room for improvement of heat transfer by a suitable optimization of ribs geometry. On the other hand, for the purpose of reconstruction of older energy type facilities, it is possible to apply ribbed tubes to increase the output of the facility while retaining facility’s dimensions. Last but not least, ribs have an interesting attenuating effect, which prevents from sedimentation of solid particles present in the medium, which contributes to limitation of the occurrence of corrosion processes and it has a favorable impact on the increase of tube lifespan. That is a clear representation of general economic and ecological contribution of such tubes The heat transmission degree can be optimized by a suitable choice of rib geometry, depending on existing operating con- ditions of the equipment (boiler or heat exchanger). Each tube is tested by ultrasound or eddy current in order to ensure required quality features. Tubes are supplied in quality grades in accordance with EN 10216, JIS G3461 – 3462, ASTM, ASME A/SA 192, 209 210 A 213 and other corresponding standards. Below you can find a breakdown of size assortment of tubes with interior ribbing sup- plied by Železiarne Podbrezová a.s. as it is shown in table 17 and 18.: