Requirements on increasing the level of efficiency of high-performance steam generators have caused an occurrence of accidents on tube walls due to overheating and cracks have even been caused by burning through a pipe wall. In order to solve the issue, Železiarne Podbrezová has developed tubes with protrusive projections on the inner side.
Today, there is still the prevailing use of tubes with smooth surface for the purposes of construction as well as reconstruction of energy type facilities, despite the fact that tubes with surface structure (tubes with interior ribbing) positively influence the performance of energy type facilities.
Tubes with interior ribbing are intended for high-performance steam generators and high-pressure boilers and are also used for burners in the equipment.
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 optimisation of rib geometry
Last but not least, ribs have an interesting attenuating effect, which prevents sedimentation of solid particles present in the medium, contributing to limitation of the occurrence of corrosion processes, and it has a favourable impact on the increase of tube lifespan. That is a clear representation of the general economic and ecological contribution of such tubes.
Currently, there is an increasing demand for tubes with interior ribbing for construction of new super critical boilers. 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 the facility’s dimensions.
The heat transmission degree can be optimised by a suitable choice of rib geometry, depending on existing operating conditions of the equipment (boiler or heat exchanger). Železiarne Podbrezová, manufacturer of seamless steel tubes, has many years of experience in production of tubes with interior ribbing. The entire production process, i.e. the melting of steel, production of rolled tubes, tubes drawing, as well as the final heat processing, is carried out by Železiarne Podbrezová. Each tube is tested by ultrasound or eddy current in order to ensure the 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.