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Internal Corrosion Prevention ‘HDD’ Style
However, the usual 66,000-plus daily drivers that cross the Mathews Bridge were not lazy. The many lane closures kept drivers busy looking for alternate routes, and often meant that CRTS field technicians were working when there was the least amount of traffic, sometimes at 2 a.m.
Mother Nature brought unusually rainy weather, but CRTS field technicians and robots have endured geographical and environmental nuisances from dust storms to ice storms, onshore and offshore. The JEA’s 36-inch pipe was 1.27 miles long and weighed 2 million pounds, but CRTS’ custom robots easily navigated the monstrosity, as six pipe lengths were strung together, then readied for the full train of robotic equipment: a crawler, a battery cart, a cleaner-vacuum, an FBE coater and an inspection machine.
Coating IFJs follows a simple process: the general contractor pre-cleans and welds the pipe and then the pipe string is X-rayed. CRTS loads its train of equipment into the pipe trough, and then re-cleans each IFJ to create an anchor profile on the fresh weld metal for the coating. Next, the IFJs are coated with liquid or powder epoxy as specified and then inspected visually. Visual inspection is followed by a final dry film thickness and high-voltage holiday inspection. The inspection process enables welds to be repaired before any product is put in the pipe, thus greatly minimizing repair and/or rehabilitation.
For the JEA, the IFJs were coated with a project-specified FBE coating, 3M 6233. After the coating cured, the internal field joints were robotically tested for compliance to the dry film thickness specification and finally, a high-voltage holiday inspection brush was passed over the coated IFJ, detecting any anomalies in the applied coating. The customer was able to view all steps in real time and received a DVD copy of all activities as part of CRTS’ quality assurance pledge.
After protecting the IFJs, CRTS applied the same FBE coating to the OD field joints and topped it off with project-specified PowerCreteJ, an abrasion resistant overlay (ARO) that further protects the OD field joints. ARO was especially warranted because HDD projects are nearly guaranteed to encounter rocks and other natural debris that can damage the external coating as the pipe is pulled. The ARO layer provided a Shore D hardness of more than 85, whereas the normal FBE hardness hovers around 74, sufficient for the IFJ where no rocks or stones are likely to cause damage. Despite the extra cost, ARO coatings are much less expensive than the cost of replacing or rehabilitating pipe, and this benefit is also realized by coating the IFJs.