The aim of this paper is to discuss the existing design, develop & install a reliability improvement & monitoring system for the special casting facility (caisson and cylinder) equipped with a large size buried cylinder structure (approx. 12 m stroke length 1.1 m rod diameter) which is used for the movement of the entire casting table at the facility of one of the major producers of aluminum in the world. In order to protect the structural integrity as well as to prevent corrosion from electrolytes, the protective shell, called caisson, around the underground part of the cylinder was built which is made of a 30mm thick steel plate.
The corrosion protection to caisson (hydraulic jack casing) was by 400 micron coal tar epoxy paint to all external & internal faces, applied to steel blast cleaned to Swedish standard. No Cathodic Protection (CP) system was considered during design phase.
A structural failure due to corrosion of this protective shell (caisson) led sea water to enter the casting facility. Water has started to accumulate around the cylinder resulting substantial corrosion on the cylinder itself. Over the period, this water mixed with hydraulic oil which resulted in the stoppage of production. Our work will include the initial design of corrosion protection and monitoring activities, evidence of corrosion that led to leak on the caisson, study at the site to identify probable causes, design of additional corrosion protection and its implementation, and post commissioning monitoring data and analysis and conclusion as a minimum. Our work will highlight initial design failure. An ICCP system was implemented to protect external surface of the caisson. Also SACP ribbon anode was provided between caisson & cylinder to protect cylinder in case of any electrolyte present in future.
This case has been selected because we see this industry doesn't get much attention and there are several cases came to our attention in the recent past. The corrosion protection of caisson was designed using painting only and no CP system was considered. The location is adjacent to the sea and water table is about 5-6 meters. Cast house pit consists of metal caisson & cylinder. The piston travels up and down and usually is in a pit surrounded by a caisson.