CEMENT DOWNCOMER INSPECTION AND REPAIRS

A downcomer duct system with inleakage issues was in need of an interior inspection to accurately determine its condition and develop a maintenance plan. Industrial Access was contracted to perform a full inspection with non-destructive testing methods (NDT). The crew first had to clear the interior process duct to eliminate any overhead safety hazards, then performed the inspection and identified multiple problem areas. The team completed the interior repairs on the downcomer duct in time before the end of the outage.

A cement plant in the southern United States was experiencing inleakage in their downcomer structure, 220’ in height. Past FLIR imaging showed uneven distribution of heat at the deteriorating expansion joints and the steel cladding with holes. The client contracted Industrial Access (IA) to perform a structural condition assessment on the downcomer duct to identify other problem areas and develop a plan to prevent any further damage.

Duct surfaces gradually deteriorate due to constant erosion processes, thermal movement, and high suction pressure load inside the downcomer during the flow of hot abrasive dust. Regular inspection and maintenance work are necessary to ensure the maximum potential service life of the structure. In addition, since the client’s outage window remaining was very limited, IA strategized appropriately in order to maximize work efficiency and enable the client to go back to operation as scheduled.

To be able to enter the downcomer, IA had to provision multiple access openings in the structure. Two larger and four smaller openings were cut out on different locations of the downcomer exterior to provide access for the crew and for rope rigging purposes. Edges of these openings were ground smooth for safety. All work involving opening and closing of the access points was in accordance with the plant requirements. IA utilized rope access techniques to perform inspection work in the interior of the process duct. Later on, IA built an access platform that could travel up and down the vertical section of the downcomer, enabling the steel plate repairs to take place.

IA mobilized to perform the exterior inspection first, carrying out a visual survey of the structure’s condition from available vantage points. Once the interior access was enabled, the crew proceeded to remove any loose material deposits from the wall of the downcomer’s vertical section. This was a necessary safety measure that had to be taken before the inspectors could descend to lower elevations where overhead hazards are a risk. To ensure that risk is minimized, the team performed a hydro-wash to clear off any remaining debris which also increased the visual clarity for the inspection.

Then, IA thoroughly inspected all accessible surfaces inside the duct. All metallic components were carefully examined for signs of corrosion, defects, and anomalies. In the end, the crew determined the downcomer duct to be in poor condition. They found signs of oxidation and a large number of deformations, cracks, and holes in the duct plating and the joints. Deformations were buckling up to 6” inward, while some of the cracks reached up to 188” in length (half the circumference). Ultrasonic thickness testing (UT) was performed, and its readings indicated clear thinning of steel plate, both in the vertical section as well as the gooseneck section of the downcomer.

Considering the level of degradation of the inspected structure, the client had requested IA to use this mobilization to repair the most critical problem areas. The crew utilized the interior swing stage to safely access the duct walls and repaired all cracks, holes, and deformations by weld overlay or by welding sections of carbon steel plate to patch the affected areas. These emergency repair measures were taken in order to prevent the existing damage from progressing and consequently compromising the operational capacity of the structure.

IA worked hard to accommodate the client’s time limitations and enable the facility to return on-line with all of its structures operating properly. The most necessary downcomer interior repairs were completed and additional issues were identified during the inspection for future repair consideration. IA made recommendations for a number of preventive measures that should be taken to further prolong the life of the process duct.