June 9, 2009

“Zinc” Before You Start

by Tony Ippoliti

When considering a new welded steel water storage tank, remember to specify a preconstruction primer. As the name implies, a preconstruction primer (PCP) is a primer that is applied to a steel surface prior to its fabrication into a finished product.  In this example, the surface is steel plate that will be used to make a water tank; the preconstruction primer is a corrosion-resistant zinc-rich primer.

One benefit, to the steel fabricator, of using preconstruction primers is that it eliminates the need to abrasive blast and prime the steel plate since the plate arrives blasted and primed. Zinc-rich primers help prevent steel plate corrosion during the fabrication process and can be topcoated.

The Society for Protective Coatings has created a Paint Specification No. 30 that describes such a primer. Section 2.1.2 states “Once applied, the zinc-rich primer need not be removed. It can be welded-through, touched-up, and overcoated prior to being placed in service.”

If you’re concerned about the use of preconstruction primers on your tank project because they are new to you, you’ll be glad to know that the American Water Works Association (AWWA) D102 Standard Coating Steel Water Storage Tanks accepts the use of preconstruction primers. Paragraph 4.4.1 requires that all

“… coatings used on wet interior surfaces of the tank, shall have been tested and certified for potable water contact in accordance with NSF/ANSI 61. They shall have been evaluated for long-term fresh water resistance and the system shall have demonstrated satisfactory service in fresh water for at least eighteen months.”

You get two benefits from the evaluation in the AWWA requirement above: that no contamination of the drinking water in your tank occurs and that no blistering of the coating in your tank occurs.

Since 2006, the AWWA D102 Standard has allowed preconstruction primers to be used on water tanks.  Specifically,

“… preconstruction zinc-rich primers, specially formulated for welding may be shop applied without weld margins, so long as the weld-through primer is compatible with the paint system primer and meets testing and certification requirements.”

When you specify and allow the use of an NSF/ANSI 61 accepted zinc-rich preconstruction primer on your new water tank, you will have the beginnings of a protective coating system that is both corrosion-resistant and complies with the AWWA D102 Standard.

Compliments of Blastech, Mobile AL

Compliments of Blastech, Mobile, Alabama

What additional PCP-related questions do you have?

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