Savante's internal caisson inspection system K-ZON delivers real time accurate, clear and valuable data on caisson and riser condition.

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K-ZON: An advanced NDT Caisson Internal Inspection and Mapping System. 

 

Challenge:

Our client had previously suffered a fire-water lift caisson failure around a circumferential weld just beneath the splash zone.  Believed to be a result of an internal liner breakdown, a lack of effective cathodic protection and the use of dissimilar metals between firewater pump string components and the caisson fabric; this resulted in a dropped object incident and attracted the attention of a regulatory authority.  With three redundant firewater caissons of similar design, age and maintenance history; it was a requirement of the incident close-out response that all three remaining caissons be visually inspected and subjected to advanced 3D laser NDT.

 

A variety of third-party subsea inspection contractors had previously deployed ultrasonic and magnetic-field sensing techniques with results of various quality and ambiguous conclusions.  Micro-ROV inspection systems had also been deployed within the caisson but found to be lacking the power necessary to develop reliable measurements given surge conditions therein.

 

Savante were asked to develop, from first principals, a high-resolution 3D inspection laser and deployment solution system to look for evidence of preferential root weld corrosion anomalies within the circumferential weld and potential fretting issues in the parent base metal. 

 

Solution:

Following proving trials of the system, a two-man team was deployed to the platform.  Savante's K-ZON laser inspection and deployment system was gravity fed into each caisson to the heat affected zone (HAZ) surrounding a specific circumferential weld below the waterline in the splash-zone.  Two sponsons were removed from the K-ZON powered centraliser in order to get the tool to pass through a set of 120mm separated pump-retaining bars.  Controlled remotely from a topside unit; marine growth and loose residual coating was removed from the area using the K-ZON onboard 4k high definition camera and directing a remotely-actuated cavitation-blaster cleaning head.  A 500mm wide band was cleared from the area, extending 360 degrees around the caisson interior. 

 

Savante's marinised dual-head laser scanner and microscopy system was deployed onto the K-ZON rotation encoded head and swept through 360 degrees.  This enabled live simultaneous views of the circumferential weld to be acquired continuously from viewpoints above and below and combined with a high resolution topographic cross section of the weld and the HAZ area.  The depth of defects, where noted, were referenced to a vertical baseline, averaged over the HAZ parent metal and photographed. 

 

Results:

A visual record of the area was produced; surface defects and areas of preferential root weld corrosion were identified, sized and recorded.

 

Testimonial:

Firstly, I’m very satisfied with the detail of the results and the processing that has been completed to highlight salient points. Grants team have done a pretty remarkable job in getting such a detailed picture of the profile given the nature of this inspection location.
— Anon Proj Engineer, US IOC, Engaged Savante on Internal Caisson Inspection Project (UKCS)