The most common form of cracking found in industrial boilers is transgranular cracking which occurs primarily due to cyclic stress. To find the cause of transgranular failures, both the design and the operating conditions of the boiler must be analyzed. Straight tube, shell-and-tube waste heat boilers frequently develop tube and tube sheet failures due to the demands of the unequal stresses. This is primarily caused by the uneven distribution of hot gases across the face of the tube sheet.  Leaking problems are created when the tubes come loose. Imposed stresses can cause transverse cracking of the tubes, even if they are securely welded.

In mechanisms that are designed to allow steam pockets to form within a unit cyclic overheating quenching can also occur, leading to transverse cracking of tubes and, occasionally, shells. This type of cracking arises in the area of greatest stress and results in primarily transgranular cracks.

Some intercrystalline cracking may develop in this type of failure whether or not free NaOH is present. The most common type of cracking is still across the grain structure of the metal. Due to it being mechanically induced, the cracking happens despite boiler water chemical concentrations. There can also be a number of pits adjacent to or in line with the cracking – another specific indicator of apparent mechanical stresses. Any corrosives present to contribute to the formation of these pits. The normal reaction between iron and water is sufficient to cause pitting at breaks in the thin oxide film formed on freshly exposed surfaces under stress.