A project team of the National Shipbuilding Research Program (NSRP) has determined that higher relative-humidity conditions can be allowed in certain situations during surface-preparation and coating operations.
The determination will contribute to cost savings for tank-painting work performed during Navy ship construction and repair, the project team has concluded. Changes in a NAVSEA standard on relative humidity in such painting programs will take effect in the fiscal-year 2011 version of NAVSEA Standard Item (NSI) 009-32
The project team conducted a review of the technical basis for a current Navy requirement for relative humidity conditions for painting work in a shipboard tank or void space. In such projects, NAVSEA NSI 009-32 requires maintenance of relative humidity at a maximum of 50% from the start of surface preparation to cure of the topcoat. The standard “can be a significant cost driver in tank painting work performed during ship construction and repair,” the NSRP team stated in an announcement on its review and conclusions.
The project team conducted a review of the technical background of the current requirement, as well as literature and data from paint manufacturers. Then, working with NAVSEA and industry partners, the team developed proposals for solutions that relax the requirement in situations where the cost is high and the technical risk is insignificant.
The project team, led by Elzly Corp. for the NSRP Surface Preparation and Coatings Panel, explored a number of concepts to reduce the cost of this requirement while maintaining the high quality required by the Navy. As a result of the project, the requirement to maintain 50% relative humidity was relaxed to the less stringent 85% maximum relative humidity requirement for the following four situations:
• Recoating chain lockers and Collection, Holding and Transfer (CHT) tanks;
• Components painted in a shop for later installation in a tank;
• Small areas of “touch-up” work; and
• The period of time between cure-to-touch and full cure.
“The changes will have an immediate impact on the cost to paint Navy tanks where dehumidification is required due to the ambient relative humidity,” the project team said. “In U.S. shipyards, ambient relative humidity is below 50% only about 10% of the time. However, if painting can occur when relative humidity is as high as 85%, most shipyards can paint 80% of the time without dehumidification equipment.”
The panel noted that dehumidifying paint shops to meet the 50% requirement “can require millions of dollars worth of equipment. Allowing surface preparation and painting at 85% relative humidity obviates the need for such equipment and the energy to run it.
“In the drydock, dehumidification equipment results in cost and space constraints. The ability to move dehumidification equipment before touch up and full cure is completed means less equipment is needed for a series of tanks.”
The project Final Report is available for download here.
More information: National Shipbuilding Research Program, email firstname.lastname@example.org.