Delamination of Coating from a Ship’s Hull Robert B Leggat, phD JPCL Webinar 18 July 2018

Aircraft Carrier in Dry Dock Freeboard Deep Load Line (DLL) Boot Top Light Load Line (LLL) Underwater Hull U.S. Navy photo by Mass Communication Specialist 1st Class Joshua J. Wahl

Coating Application Sequence

Field Investigation U.S. Navy photo by Photographer's Mate 2nd Class Steven King

Coating Peeling on Boot Top Starboard side facing aft Portside facing aft

Coating Peeling on Freeboard Portside- grey polysiloxane peeling in band within 1 ½ feet of DLL

Sampling Locations All samples mechanically chipped to bare metal and Upper: Intact Coating in Freeboard All samples mechanically chipped to bare metal and showed cohesive failure within red anti-corrosion primer Middle: Peeling Coating in Freeboard Near DLL Lower: Peeling Coating in Boot Top

Laboratory Investigation 1. Why did the gray polysiloxane coating disbond in the freeboard just above the DLL? 2. Why did the anti-fouling coating disbond from the anti-corrosion in the boot top?

Paint Chips from Freeboard Upper location: Grey polysiloxane / Grey anticorrosion / Red anticorrosion Middle location: Grey polysiloxane / Red antifouling Grey anticorrosion / Red anticorrosion 10 mils

Paint Chips from Boot Top Solvent rub test confirmed that disbonding occurred between red anti-fouling and gray anticorrosion layers Black Antifouling Coating 10 mils Red Antifouling Coating

Catalytic Reaction with Copper Mix Ratio Analysis Nitrogen Analysis of Gray Anticorrosion Layer Oxidation In Furnace Catalytic Reaction with Copper NOx Detection by IR N2 Hardener component of the gray anticorrosion coating contained polyamide and polyamidoamine Compared to properly mixed 1:1 control sample, 2 out of 7 gray anticorrosion coating chips had a proper mix ration of 1:1, while 5 out of 7 had excess nitrogen with mix ratios ranging from 1.05 : 1 to 2 : 1.

Mix Ratio Analysis FTIR Analysis of Gray Anticorrosion Layer Band Intensity Comparison 1506 cm-1 (epoxy) vs 1454 cm-1 (hardener). Confirmed results of Nitrogen Analysis Indicating excess hardener in gray anticorrosion coating

Recoat Interval Study 2 Hours 4 Hours 40 Minutes 6 Hours 8+ Hours Adhesion markedly better for recoat window between gray anticorrosion coating of 2 hour vs longer times

Tack Time Test Ratio of A to B Substrate Time from AC Application until No Longer Wet Time from AC Application until No Longer Tacky 1 : 1 Steel Panel- Same as Recoat Study 1 hour and 45 minutes 4 hours and 15 minutes 1.4 : 1 2 hours 3 hours Glass Panel - 6 mil WFT Drawdown 1 hour and 45 minutes 1.05 : 1 4 hours 1.1 : 1 30 minutes

Conclusions Disbonding above the deep load line (DLL) was caused by application of the polysiloxane over the antifoulant coating (AF), instead of the anti-corrosion coating (AC). There was off-ratio mixing of the gray epoxy AC in some cases. Spontaneous disbonding and poor adhesion of the AF below the DLL resulted from exceeding the tack time of the AC which was aggravated by the off-ratio mixing

Recommendations The shipyard and coating contractor should review QA/QC records to determine in which areas tack time was likely to have been exceeded. The coating should be removed in the areas where peeling is observed or have been identified as being susceptible. Coating should be removed by hand or mechanical tool cleaning and/or high pressure/ ultrahigh pressure water blast cleaning.