Thermal
Peak Temperature: The inner part of the shroud being in direct contact with the steel reaches a maximum temperature of 1550-1600 degrees centigrade. The temperature is high from the refractory standpoint and the material is to be selected which can withstand such high temperatures. Alumina or magnesia refractory is preferable.
Thermal Shock: Thermal cycling is very high for the shroud when put into service. The inner side of the shroud being in contact with steel is at an elevated temperature whereas the outer part is at the lower temperature being in contact with the environment. The difference in temperature is relatively high leading to high thermal stress. The thermal shock is high especially during heat change over, ladle-assisted open and during tundish change. During these type of incidences the temperature on the inner side of the shroud cools down and when the ladle further re-opens it again comes in contact with the temperature of the new metal flowing through it and thus it suffers from the thermal shock owing to time delay (or temperature loss) encountered in such circumstances. Thus carbon is added to deal with this phenomenon. Thermal shock makes the shroud more susceptible to vertical crack due to radial expansive forces.
Mechanical
Impact: The impact on the shroud is considered to be relatively low except in certain conditions like an inclined shroud.
Abrasion: The abrasion of the shroud surface is high when the throughput from the ladle is high. It is also dependent on the size of the shroud. The flow from the ladle is asymmetrical and becomes even more pronounced especially during ladle chocking condition which results in the bouncing of the steel around the shroud. The wear on the sides of the shroud is the manifestation of such flow chemistry. The slag line also suffers from abrasion during turbulent (fluctuations of level) molten bath level. The ladle shroud suffers from abrasion even during ladle change where the metal bounces back from the molten bath when un-submerged opening practice is followed. The outer part of the shroud suffers from abrasion from metal as well as slag during its course of service.
Applied stress: The applied stress on the shroud is low as its expansion is not restricted by any other mechanism. It only comes into play when the shroud bracket comes into the picture but even that is not substantial.
Chemical
Dissolution: The dissolution of the refractory depends on the compatibility of the slag with that of the material used. The tundish slag has a broad range of chemistry but becomes acidic is nature when low-cost rice husk is used as the tundish covering compound. A range of tundish slag composition is outlined as follows: Al2O3-3-33%, CaO-1-40%, SiO2-2-89%, MgO-1-20%, FeO-1-4%. Thus alumina-based or spinel based material is generally preferred. Too much of slag volume may also restrict shroud life.
Penetration: Penetration is accentuated by the low viscosity slag or highly wetting slag/metal. The slag line area can become susceptible to penetration. But the area of shroud neck is an area more prone to such an attack because during shroud cleaning high-pressure oxygen is used which produces low viscosity, high-temperature slag/metal which can penetrate deep into the refractory.
Thermo- Mechanical
The strain of thermal expansion-Applied Stress is low but the thermal strain is prevalent due to temperature gradient and prevalence of thermal shock.
Chemical Mechanical and thermomechanical chemical
Spalling of the penetrated zones- The wear is high in the neck region owing to shroud cleaning by oxygen but the impact and applied stress are low. Wear takes place on the inner side and bottom of the shroud, outer slag region and many other positions in the shroud but the cumulative action of thermal, mechanical along with chemical action is quite unlikely.
