May 2017

Guide Tube Corrosion Mitigation

Flexlife has developed a number of solutions intended to mitigate corrosion within the internal annulus of guide tubes.  This region, whilst providing physical protection for the conductors therein, can be susceptible to corrosion and is a difficult area to access or inspect.


The FlexGelLD product is currently TRL7 (API17N) with a number of systems in use worldwide.  The basic technology is an engineered gel with Specific Gravity and Viscosity tuned to suit specific applications.  It is injected as a Cefas accredited premix solution from topsides with no need for vessel intervention.  Subsequent Inline Inspection has demonstrated that once the product is injected into the guide tube it effectively mitigates any further external riser corrosion, and internal guide tube degradation, thus obviating the need to carry out costly replacement.

Further Development

A further development of the FlexGel® technology has been used as a temporary pipeline plugging medium within platform rundownlines.  In this instance the FlexGel-XLD is product is further engineered to be injected as a Specific Gravity and Viscosity tuned liquid which cures to become an elastic solid once pumped to the desired location.  Again application does not require vessel installation with the polymer being activated and mixed topsides and immediately injected into the desired location.

Combination Approach

Flexlife wishes to offer a combination approach to address the issues of internal guide tube, corrosion and/or bellmouth abrasion.  This concept has been effectively trialed onshore and is a four stage operation.  

·         Firstly, FlexGel-XLD, Low Density Cross Linking Polymer gel is activated and mixed on deck as a two-part compound.  The polymer activation shall be tuned to ensure that sufficient time can elapse for it to be displaced into position prior to curing to become an elastic solid plug at the base of the guide-tube.  The volume of the FlexGel-XLD product shall be calculated to be sufficient to plug the J-tube, isolating the J-tube from the effect of changing vessel draft, but minimised to facilitate the eventual removal of the riser.

·         Secondly, the activated FlexGel-XLD is pumped into the guide-tube where it forms an immiscible liquid, floating atop the seawater.

·         Thirdly, the FlexGel-XLD is displaced into position using FlexGelLD thixotropic gel which has a lower density.  The two polymer variations are immiscible, forming a boundary from one another during this deployment.

·         Finally, once the appropriate quantity of FlexGelLD has been pumped, it will have displaced the seawater out of the base of the guide-tube, leaving a plug of FlexGel-XLD in situ.  This plug is held in equilibrium by the head of FlexGelLD curing after installation to form a cross linking elastic solid polymer.

This technology is suitable for FPSO application where vessels are subject to fluctuating draft and also for platform application where leaking base seals can lead to inhibitor leaching and internal guide tube corrosion.