MARINELINE® & CHEMLINE® COATINGS FOR INDUSTRY

APC Article Reprints

It's all in the prep. Beyond the science that makes the coating effective, the most important aspect to the success is proper preparation and application.
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The MarineLine® tank coating system from Advanced Polymer Coatings is called upon to carry acids, caustics, alkalis and many other chemical cargoes on regular basis. The coating's range protects the tank from corrosive attack, and the cargoes from contamination while traveling between ports.

Pre-Blast Inspecting Weld Finish
Pre-Blast Checking Surface Profile
Grit-Blasting
Final Approved Tank Coating

The polymer-based technology used in the coating is noteworthy. But beyond the science that makes the coating effective, the most important aspect to the success is proper preparation and application.

As such, APC has developed a 7-Step Application Program to ensure the tanker owner has many years of profitable service with the vessel. These steps include:

  • Pre-Blast Preparation;
  • Blasting;
  • Spray Application;
  • Inspection;
  • Heat Cure;
  • Final Inspection and Sign-Off;
  • Final Repairs.

Every coating faces inherent problem areas within a cargo tank. In certain locations, breakdowns may be more prevalent; areas where excessive stress is caused by structural issues such as weld seams, edges, corners and others. That is why it is vital to ensure surface preparation is done in accordance with recommended specifications, and care is taken to avoid contamination during the coating application.

PRE-BLAST

In the industry, more than 90% of coatings issues are related to poor surface preparation. That is why APC believes in proper inspection at each step of the process. At the pre-blast stage our goal is to begin the process of ensuring the coating achieves maximum adhesion to a clean surface, without any design or structural defects that could lead to premature coating failure.

In the weld and grind inspection, it is imperative to check for defects, sharp corners, and difficult to coat areas such as weld splatter, gouges, poor welding, and delamination in the steel. If recoating an existing vessel, the surface preparation team should also look for pitting and mechanical damage from previous use. Surfaces should also be checked for surface contamination prior to coating.

Other important aspects of the set-up operation include staging, proper dehumidification, ventilation, surface protection, and rain protection.

BLASTING

Abrasive blasting cleans the tank surface to promote proper adhesion. Blasting abrasives should be clean and free of contamination. MarineLine® specifications are to grit blast to a SA 2.5 standard with a 75-100 micron profile.

It is important that proper dehumidification and dust collection units are set up prior to the start of abrasive blasting. The inspector performs environmental tank conditions inspections, humidity, temperature and dew point, prior to commencing any work.

After the initial blast, the inspector checks that the steel surface is clean and at the recommended profile, and for any contamination by chlorides or hydrocarbons, which would then require a tank wash. He also checks welds, pits and steel for potential problems that may have been exposed during the initial blast.

Next, final blasting commences, followed by a blow down and vacuuming of the tank to remove all dust and contaminants.

SPRAY APPLICATION

In the coating application, it is vital that dehumidification equipment run at all times to ensure the steel does not begin to flash rust and that moisture does not form on the surface, or penetrate the fresh coating after application.

MarineLine® coating is provided in separate containers and must be thoroughly mixed in the proportions supplied. The tank coating is applied by airless spray in a cross-hatch method to ensure proper coverage. The high solids content of MarineLine® provides a better coverage rate, and limits the opportunity for pinholes and problems to arise. MarineLine® is applied in two coats, with a stripe coat of all welds and critical areas in between.

The inspector checks the application between coats to ensure proper thickness and total coverage of areas, especially at the seams, welds, and corners, and also the surface for cleanliness, proper curing and over spray. Upon completion of the application, the inspector performs Dry Film Thickness (DFT) tests to ensure the thickness meets coating manufacturer specification.

Inspectors also do spark tests of the entire tank coating to ensure it is pinhole free. While performing these tasks the inspector performs visual inspections for any areas that could cause problems such as overspray, runs or sags in the coating.
Upon completion of the application phase, the cargo tanks are heat cured to exacting specifications to remove solvent entrapments in the coating and fully cure the polymer.

Inspection of the coating process is performed during the entire process of the application by technical personnel, ensuring the cargo tanks have been coated to the highest quality standards. The inspector also trains the crew on proper repairs.

After the final inspection, the vessel is put out to sea trial. Any final repairs and touch-up work is then completed as needed. The vessel is now ready to carry cargoes recommended by the coating manufacturer after leaving the shipyard.