Chains in wet and long-dry rotary cement kilns usually work as a removal of the moisture from the raw cement materials (mud), and it is also cleaning the kiln shell by transporting materials, crushing the mud rings, reducing the dust amount, and reducing the kiln exit gas temperature. Figure 1 shows a sketch to the rotary cement kiln including the chain locations (called also curtains) and the process of cement manufacturing . The raw material enters the rotary cement (wet feed) with a temperature of 40 °C, while it discharges from the kiln with a temperature of 200 °C. The gas enters the kiln with a temperature usually ranged from 700 to 760 °C and exits with a temperature of 180 °C. These ranges of temperatures input and exit are controlled by the chains; any issues in the chains including failure due to breakage during the kiln operation can affect the product (clinker) quality and may result in air pollution. Figure 2 is a real image of chains curtain inside rotary cement kiln at “Kufa cement plant” which is under concern in this study, while Fig. 3 shows the relationship between energy consumption with and without using chain curtains . The use of chains which made of carbon steel has caused in reduction in energy consumption from 1870 to 1730 kcal/kg, while using heat resistance chains cased in energy consumption of 1500 kcal/kg. Chains usually experience complicated thermo-chemical-mechanical conditions during cement kiln operation. Gas temperatures can reach to 800 °C in the first row of chains, while the temperature of raw material in contact with the chains is about 200 °C as shown in Fig. 4 . Materials selection of chains usually depends on the location and the type of fuel used in cement kiln, high resistance steel grades are preferable in the first rows of chain curtains, while cheaper steel grades can be used in a distance far away from the flame to reduce the cost. Steel grades include carbon steel (AISI C1020, C1022, C1035), alloy steel (SAE 4140 and 8620), stainless ferritic steel (AISI 8F, 9F, and 10F), stainless austenitic steel (AISI 304, 329, 309, 310, and 321), and the very high resistance steel grades which have been developed by adding Mn element to increase the protection of Ni and Cr alloying elements. Figure 5 shows the ideal suggested layout of chains designed by Heko Ketten company, Germany, which depends on the fuel type . Kiln chains usually last for maximum of 10–12 months depending on the operation conditions and the type of steel grades [Kufa cement plant records]. Issues of corrosion, deformation, and brittleness especially in the top ring of the chain are the most causes of the chains failure. Figure 6a–e shows different types of chains failure after serving for different period of time ranging from 6 to 8 months [Kufa cement plant]. The failures include (a) reduction in thickness and deformation, (b) oval deformation in the top ring, (c) reduction in thickness, oval and twisting deformation in the top ring, and (d) brittle cracking.
Previous work on cement kiln chains is limited for industrial companies which produce these products such as Heko Ketten, Germany, and AMH, Canada. Corrosion and chromium segregation represent the most issues that can lead to kiln chains failure. Stavrev and Dikova  investigated the structural changes of cement kiln chains grade DIN 1.4892 105MA Ni, Cr, Mn steel. They found that a reduction of 30% of chains thickness has occurred after 120 days of continuous service as a result of the corrosion and the mechanical effect of the mud. The microstructure of the chains which exposed to a temperature fluctuation above 700 °C was found to experience recrystallization. This in turn has resulted in a pit character and corrosion-fatigue cracks under the cyclic mechanical load. This crack was then propagated toward the depth of the chain and caused the final failure by breakage. Park et al. 2013  applied immersing of weathering steels in 16.9 vol.% H2SO4 + 0.35 vol.% HCl at 60 °C in order to investigate the effect of Cr on corrosion resistance. Cr segregation at grain boundaries was found to increase when Cu elements exist in steel. They found that microgalvanic corrosion was the mechanism of Cr segregation as the grain acts as anode, whereas the grain boundary acts as cathode. The localized segregation of Cr has been found to cause in pitting corrosion which in turn caused in a reduction in the steel thickness. Saraf et al.  found that Cr diffusion in Ni/Cr steels is the main issue that can reduce the corrosion resistance in steel. The Cr was found to segregate at the high-angle grain boundaries, and the angular misorientation between two grains is the driver of Cr segregation. Laws and Goodhew  investigated the relationship between Cr segregation and grain boundary structure of AISI 316 stainless steel using analytical electron microscopy technique (AEM). They found that the summation of boundaries which is equal to 9 was resulted in more Cr concentration rather than other grain boundaries. Defilippi and Chao  found that a band-like segregation pattern of chromium and molybdenum occurs in 434 stainless steel when hot rolling carried out in the temperature range of austenite and ferrite phase diagram. This type of segregation has classified as detrimental because it has led to ridging recrystallization.
The current work aims to understand the causes of kiln chains failure of Kufa cement plant by taking many samples of chains from different locations starting from the first row until 28.2 m. Two time periods of continuous operation have been chosen (30 and 180 days) in order to understand the progress of failure with time. Chemical analysis, optical microscopy, and SEM-EDS techniques have been employed to investigate the possible phase change, grain growth, and elemental segregation.