In the past 20 years, Axess Group has developed safe, lean and innovative methods for lifting operations, allowing us to replace caissons faster and at a fraction of the cost of what it used to be. We have gained substantial experience within the field and replaced many caissons in recent years, with excellent feedback from our clients.
Caissons are key components of steel jacket structures – one of the most common types of offshore platform foundation in shallow and mid-water. Damage to caissons can cause severe problems if not dealt with correctly, with production shutdown and major accidents being the most critical.
Common types of damages:
- Corrosion and resulting wall thickness reduction due to wear and damages in surface treatment, lack of cathodic protection
- Galvanic corrosion problems due to the use of dissimilar metals in caissons and pumps
- Structural fatigue cracks due to dynamic movements and loads
Caissons come in many different designs. For a typical mid-water installation, they have a length of 50 to 100 meters and weigh 20 to 40 metric tons. Caissons are usually manufactured and installed at the same time as the jacket structure itself. They are usually not designed to be replaced during the expected lifespan of the platform. Most are produced with either welded or flanged joints, with welded joints being the most common.
It is impractical to replace or install caissons in its complete length, thus, it must be done section by section. Removing the old caisson by cutting it into smaller sections can be challenging and time-consuming, if not planned and executed accurately. Furthermore, as the reason for replacement is typically excessive corrosion or fatigue cracks, it is very important to secure the caissons to prevent them from breaking during these operations.