The heater of blast furnace intended to provide hot blast and has a metal casing lined inside with refractory bricks. The technological process involves cyclic changes of gas temperature in the heater from 400 to 1200 °C (673 to 1473 K) with cycle duration of 3 h. After some operating time, cracks appear in the casing. Internal pressure in the apparatus is low; nevertheless, the cracks are dangerous because the stream of hot (1200 °C) oxygen-enriched air can damage surrounding structures. A way to prevent cracks depends on the mechanism of their formation. Three possible reasons of the crack formation were considered: uncompensated forces caused by thermal expansion of the entire structure, vibrations, and thermal stresses due local uneven heating of the casing.

The observed cracks have different orientations and in some cases are located sufficiently close to each other. This pattern is characteristic for thermal cracks and is not typical for cracks caused by mechanical loads and/or vibrations. Numerical analysis shows that the non-uniformity of temperatures may cause the thermal fatigue cracks despite the fact that the non-uniformity observed on the outer surface of the casing is small enough. Fractographic studies confirmed the thermo-fatigue nature of the cracks. As a possible measure to prevent cracking the usage of 2-layer casing was analyzed, numerical estimations proved potential effectiveness of such solutions.

高炉加热器，旨在提供热风，并在其内部衬有耐火砖的金属外壳。该工艺过程涉及加热器中气体温度从400到1200°C（673到1473 K）的循环变化，循环持续时间为3 h。经过一段时间的使用后，外壳出现裂缝。设备内部压力低；但是，裂纹是危险的，因为热的（1200°C）富氧空气流会损坏周围的结构。防止裂纹的方法取决于裂纹的形成机理。考虑了裂纹形成的三个可能原因：由于整个结构的热膨胀，振动以及由于套管局部不均匀加热而引起的热应力而产生的未补偿力。

观察到的裂纹具有不同的方向，在某些情况下彼此之间的距离足够近。该图案是热裂纹的特征，而不是由机械负载和/或振动引起的裂纹的典型特征。数值分析表明，尽管在壳体的外表面上观察到的不均匀度足够小，但温度的不均匀度仍可能导致热疲劳裂纹。分形学研究证实了裂纹的热疲劳性质。作为防止开裂2层套管使用的一种可能措施，分析了数值估计，证明了这种解决方案的潜在有效性。