The Challenge of Dismantling Double-Wall Ammonia Tanks
Decommissioning an aged ammonia storage tank is one of the most hazardous operations in the mechanical EPC sector. Anhydrous ammonia is highly toxic, corrosive, and requires extreme precision to vent, purge, and dismantle safely.
Traditionally, tanks are dismantled from the top down. This requires massive amounts of external scaffolding around the entire circumference of the tank. Workers are forced to perform hot work (plasma cutting or gas cutting) at extreme heights of 25 to 40 meters, increasing the risk of falls, dropped objects, and compromised crane stability during heavy shell lifts.
"HAIL completely removed the working-at-height risk equation by introducing the Reverse Jacking method for tank decommissioning in India."
What is Reverse Jacking?
The Reverse Jacking method flips the traditional dismantling process upside down. Instead of cutting from the top, hydraulic jacks are installed inside the tank to lift the entire structure.
- Hydraulic Lifting: A synchronized hydraulic jacking system lifts the entire tank shell slightly off the foundation.
- Bottom Ring Cutting: The bottom-most shell course is cut manually or mechanically at ground level.
- Lowering and Repeating: The tank is lowered back down, the next ring is cut, and the cycle repeats.
By using this method, 90% of the cutting, rigging, and material handling is done exactly at ground level. This eliminates the need for full-height scaffolding and drastically reduces the project timeline.
Case Study: Birla Copper Ltd., Dahej
HAIL was contracted by Ostwal Phoschem (India) Ltd. to decommission a double-wall ammonia storage tank and a 55-metre high flare stack at the Birla Copper facility in Dahej, Gujarat. We deployed the reverse jacking method to execute the project with absolute safety.
Step 1: HAZOP & Pre-Mobilization Studies
Before a single piece of steel was cut, HAIL's engineering consortium, along with RINA Consulting, performed an extensive Hazard and Operability (HAZOP) study. We conducted an aged-plant structural fitness assessment to ensure the tank roof and remaining shell could withstand the hydraulic jacking stresses.
Step 2: Nitrogen Purging & Gas Freeing
Residual ammonia in the annular space and inner cup was handled using controlled drain-down procedures. We flushed the system with water and followed up with rigorous nitrogen purging. Scrubber venting was utilized to neutralize any escaping ammonia vapors. Hot work permits were only issued after multiple gas-free certifications.
Step 3: Execution of Reverse Jacking
HAIL mobilized a specialized lifting trestle system. The outer roof was separated, and the inner and outer shell courses were dismantled sequentially using the synchronized jacks. As each ring was brought to ground level, our cold-cutting teams sectioned the plates for immediate scrap dispatch.
Step 4: Flare Stack Dismantling
Simultaneously, the 55-meter flare stack was dismantled. Rather than felling the stack, our heavy lift division deployed owned 200 MT cranes to section the stack into engineered segments, lowering them safely inside an operating plant environment.
Results & Key Takeaways
- Zero Incidents: Maintained a flawless safety record throughout the high-risk operation.
- Schedule Compression: Completed the dismantling approximately 35% faster than the top-down conventional method.
- Cost Efficiency: Avoided the massive rental and erection costs associated with full-height external scaffolding.
HAIL is currently the only mechanical contractor in India utilizing the reverse jacking method for double-wall cryogenic and ammonia tank decommissioning. For operating refineries, chemical plants, and fertilizer complexes, it represents the safest and most efficient path to clearing aged infrastructure.