The U.S. Navy is loosening its longstanding requirement that pre-construction primers (PCPs) be removed from all critical-coated surfaces, a policy change that will save more than $7 million a year, according to a new study.
“Past studies and the present work conclusively demonstrate that pre-construction primer can be retained without impacting coating performance,” concludes “Retention of Pre-Construction Primer,” a new Surface Preparation and Coatings Panel Project Report from the National Shipbuilding Research Program.
The report is the latest in a 30-year collection of studies that have supported retaining inorganic zinc pre-construction primers as a cost-saving measure that does not affect service life. Navy practice currently requires removal of inorganic zinc pre-construction primers on all critical-coated surfaces.
Study on Repair, New Construction
In the new study, researchers documented the procedures used to retain pre-construction primer during repair of the USS Vicksburg and during construction of the T-AKE class. In both cases, the pre-construction primer was retained on steel in critical coated areas.
Based on those results, the project team developed wording for insertion to Navy Standard Item 009-32 to allow pre-construction primer retention during Navy ship repair. The team estimates that the change can save the Navy more than $7 million per year, most of it in new construction costs.
The change, approved at the July 2010 meeting of the NAVSEA Standard Specification for Ship Repair and Alteration Committee (SSRAC), will require brush blasting for secondary surface preparation of pre-construction primer, except in fuel-related tanks.
The change will not allow retention or pre-construction primer in potable water, reserve feedwater, and freshwater drain collecting tanks, nonskid applications (MIL-PRF-24667), and single-coat applications (MIL-PRF-23236 Type VII Class 18/x). But these exceptions may eventually be lifted as well, researchers indicated, once more research is available on secondary surface preparation and PCP compatibility with single-coat materials.
Inorganic zinc pre-construction primers are a special class of inorganic zinc primer, with drastically reduced zinc pigment content designed to withstand welding and handling during fabrication before they are incorporated into the permanent finished structure. Corrosion prevention is required, the researchers note, but only from the time the primer is applied until the components are joined into a completed structure.
The Navy has historically removed PCP to facilitate welding or when the primer was deemed incompatible with the final coating system.
The new research notes that there is no single standard for pre-construction primer material, although “the nearest thing” is the International Maritime Organization (IMO) Resolution (MSC215(82)) Performance Standard for Protective Coatings for Dedicated Seawater Ballast Tanks in All Types of Ships and Double-Side Skin Spaces Of Bulk Carriers (Pspc).
That measure specifies inhibitor-free zinc silicate shop primer or equivalent. However, the researchers note, “equivalence is not defined,” leaving the determination to the manufacturer or classification society.
PCP selection is driven by welding as well as coating issues. The primer can have an effect on welding speeds and quality. The composition of the primer can have health and safety implications for the welding process.
“Applying Navy-specified coating systems has historically required complete removal of the pre-construction primer,” the report says. “However, as a result of advances in primer and epoxy coatings, it has become common to retain PCPs during commercial shipbuilding.”
Researchers say the Navy can do the same if it addresses three issues: primer application, secondary surface preparation, and inspection of the PCP surface before coating application.
Especially significant, the team says, is the need for secondary surface preparation before the final coating is applied. Researchers said that step may consist of solvent cleaning, power tool cleaning, pressure washing, abrasive blasting, or a combination of these methods, but they noted reluctance by coating manufacturers and the Navy to allow pressure washing until compatibility has been demonstrated.
As a result of this project, Navy Standard Item 009-32 has been changed to allow retention of PCP. The change will officially take effect with the FY2012 version of the standard, but “it may be used on individual projects before the effective date of the standard item if agreed to by the shipyard and Navy,” according to the report.
The report notes continuing concern over the performance of the newer single-coat rapid-cure coatings when applied over pre-construction primer. This issue has not been tested and should be evaluated, the researchers say.