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Caisson Replacement

Offshore installation lifetime extension programs

The oil and gas industry has since the very beginning of the industry continuously developed new and improved existing technology which has made it possible to produce oil and gas in more efficient and sustainable ways. The last decades this development has made it possible to increase economically viable extractions rates from existing fields to a level that was unthinkable, when many of the present platforms and  infrastructures was designed and installed during the 1980’s, 1990’s and early 2000’s. This development has created a strong demand in the marked for innovative and efficient ways to support lifetime extension programs of existing platforms and infrastructure. As many platforms have a typical design life of around 20-25 years only, equipment and structural elements will often need replacement or major overhaul if a substantial lifetime extension is to be approved by authorities.    

Caissons – key component of the offshore jacket structure design

One of the most common offshore platform foundation designs worldwide, in the shallow and mid-water depth segment, is the steel jacket structure.

This is usually an economical, robust and well tested design with a long lifetime expectancy. However, one of the typical components of a jacket structure, that is prone to suffer from excessive corrosion and fatigue life problems, is the seawater inlet and output pipes – the caissons.

Common risks associated with caissons:

  • Corrosion and resulting wall thickness reduction due to wear and damages in surface treatment, lack of cathodic protection etc.
  • Galvanic corrosion problems due to use of dissimilar metals in caissons and pumps
  • Structural fatigue cracks due to dynamic movements and loads etc.

Caissons come in many different designs, but will for a typical mid-water depth installation have a length of 50 – 100 + meters in length with a weight of 20 – 40 metric tons. Caissons are usually manufactured and installed at the same time as the jacket structure itself, consists of either welded or flanged joints, and are usually not designed to be replaced during the expected lifetime of the platform.

Technology development

To energy companies caisson issues can cause severe problems if not dealt with correctly, with longtime production shutdown and major accidents being the most critical.

For many years caisson replacement was considered too expensive and time consuming as there are examples of caisson replacement projects with a cost of almost 20 million USD for replacement of one caisson only.

As there can be 10-15 caissons on a platform, one can understand that some energy companies have postponed these replacement projects and tried out temporary repairs instead.

The last 20 years Axess Engineering has developed safe, lean and innovative methods for safe lifting operations. The recent years this technology has made it possible to replace caissons faster and at a fraction of the cost of what it used to be.

Caisson replacement

We have gained substantial experience within the field and replaced around a dozen caissons offshore the recent years with excellent feedback from our clients. Contact us for references and more details.

Caisson section connection types

As mentioned above most caissons are produced with welded or flanged joints, with welded joints being the most common. For replacement purposes it is impractical to replace or install caissons in a complete length, i.e. it has to be done section by section.

Removing the old caisson by cutting it into smaller sections can be challenging and time consuming enough, if not planned and executed accurately. As the usual reason for replacement is excessive corrosion or fatigue cracks, it is very important to secure the caisson from breakage during these operations.

That being said, the most important factor in order to succeed in a caisson replacement project is having an efficient and cost effective solution for installation of the new caisson elements. Axess Engineering have experience with both flanged and welded section design, but the recent years the pin-box connection type has proven to be a very robust and cost effective solution.

WHAT WE DELIVER

A caisson replacement project is complex and includes many disciplines and specialists. One of Axess Engineering’s keys to success is our constant search for improvements to our solutions. As we are an independent engineering company and not an OEM, we are free to offer the best possible solution to our clients at all times.

Axess Engineering strive to meet any client request, but typical deliverables can be as follows:

Planning and engineering phase

  • Project management and administration
  • Technical and engineering management
  • Design engineering
  • Structural engineering
  • Lifting method planning
  • Mechanical work and equipment planning
  • Subsea work and equipment planning
  • LCI engineering

Fabrication and procurement

  • Assistance with the procurement of new caissons, or
  • Complete delivery of design and procurement of new caissons
    • Production follow-up / inspection and quality assurance
    • Special focus on installation friendliness
  • Fabrication of custom made lifting equipment

 

Offshore execution phase

  • Installation management
  • Complete offshore crew and equipment package
    • Subsea preparation work
    • Mechanical and cutting work
    • Lifting / rigging / rope access operations
    • Subsea installation operations
    • Pin-box installation crew and / or welding crew
    • Inspection and certification work

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