===Tank lifting and remediation===

An analysis of the situation will result in recommendations for the appropriate remedial action, and what repair work should be performed, possibly including but not limited to:

*Tank lifting
*leveling
*repair and replacement of roofs and floors
*shell repairs
*reconstruction of foundations

Storage tanks should be updated to meet the highest local environmental standards, including the installation of release prevention barriers and leak detection.

Several different technologies exist for lifting tanks. The conventional methods involve [[hydraulic jacking]] equipment, while another method utilizes an [[airbag lifting system]] to elevate the tank from its base to allow for remedial action.
The main concerns when lifting a large vessel is that the method of lifting does not cause any damage to the internal structures of the tank, or to any of the critical shell connections. Most tanks are built with a [frangible weld][http://www.tankteam.com/frangible_joints.htm] at the roof to shell connection, which is necessarily a weak point, so any uneven lifting of the tank will stress this joint and weaken it further and possibly fracture it.
Roof structures can also be severely damaged by uneven lifting, the [[rafter clips]] are worked back and forth each time the tank is lifted unevenly weakening the weld to the shell, and can be damaged to the point of immediate or future failure.
Uneven lifting of the tank is the leading cause of differential rotation between columns and the shell known as [[racking]]. Racking can require complete replacement of columns and roof rafters to repair.
The only way to prevent these problems is if the tank is lifted perpendicularly and evenly using a system that prevents uneven lifting of the tank. [[Hydraulic jacks]] coupled with a [[unified fluid volume delivery system]] is the best way to lift a tank and maintain the structural integrity of the tank. Any weakening to the structural integrity of the tank, no matter how slight, will reduce the service life of the tank.
Since the whole purpose of lifting a tank in the first place was to increase the service life of the tank, and the decision to remediate the foundation and do the repairs and maintenance were based on the cost of repairs divided by the expected added service life of the tank as compared to the costs of building a new tank; then any weakening of the tank structures unaccounted for in the cost assessment will defeat the purpose of repairing the tank in the first place. So the way a large AST is lifted is critical to assure that the repairs add to the service life of the tank rather that reduce it.
Many companies are using an [[airbag lifting system]] to lift tanks. Airbag lifting systems are cheap, and so are popular with contractors. However airbags cannot perform a perpendicular lift and can not lift a tank evenly. Lifting a tank with airbags puts enormous stresses into the tank severely damaging the continuity of all the critical structures and connections of the tank. These problems are not always visible to the eye on the job site, but the tank's service life expectancy is reduced substantially below what would have been projected by the inspection process that determined the viability of the repair. An [[airbag lifting system]] should not be used to lift tanks because of this.
However any short stroke lifting system that does not have a mechanism to unify the lifting movement of the tank will cause uneven lifting of the tank including short stroke hydraulic jacks as well as airbags. However only hydraulic jacks have the capability of performing an even and perpendicular lift if a unified oil volume delivery system is used to assure each jack lifts the exactly the same.
Air is compressible, and airbags are flexible, so it is impossible for an airbag to lift perpendicularly and evenly, hydraulic oil is not compressible, and hydraulic jacks have a fixed volume so they can be made to lift perfectly evenly and perpendicularly by supplying an equal volume of oil to each jack.
However, any short stroke lifting method where the lifting equipment needs to be reset in small incremental lifts to reach full lifting height; will cause the tank to wander off of its original footprint requiring piping and attachments to be refitted. Tank Wander adds unnecessary cost and time to the schedule. Sometimes a plant may need to be shut down while the piping is being refit because it may be otherwise impossible to drain the line, this can be very costly indeed.
The only way to lift a tank evenly and perpendicularly and assure that it returns the tank directly back where it originally was is to use long single stroke high-lift jacks that can lift a tank to full height in one smooth controlled stroke. Long jacks coupled with a unified oil volume delivery system can lift tanks over ten feet high and return them exactly back onto their original footprint, eliminating Tank Wander while maintaining structural integrity of the tank preserving the service life expectancy of the tank.
Another added advantage of lifting tanks with long stroke hydraulic jacks over airbags or short stroke jacks is speed. Where it may take several days or even weeks to lift a tank with airbags or short jacks, a long stroke jack can lift a 160 foot tank to 10 feet in less than 30 minutes, and lower it again just as quickly. This can be very advantageous if you happen to be in an area where hurricanes are a threat.