Protection of Steel Piles by Selected Coatings in a Natural Seawater Environment
Authors: Escalante E. , Iverson W.P. 
Published: December 2007

Six types of coatings are evaluated for their ability to protect steel piles in offshore conditions. These coatings, which are composed of a piles in offshore conditions. These coatings, which are composed of a single-system, metal-pigmented paint and five 2-system, nonmetallic coatings on metal-filled primers, are described in detail. Results for the first 6 years of a 15-year program are presented.

Introduction

The National Bureau of Standards has undertaken the task of evaluating various protection systems for iron in seawater. The ultimate aim of the program is to develop methods for evaluating the effectiveness of these protection systems, whether they are barrier type coatings, protection systems, whether they are barrier type coatings, anodic coatings, cathodic protection, or combinations of these. The environment chosen for the program was a particularly aggressive one - an offshore test site. particularly aggressive one - an offshore test site. This paper is a synopsis of part of the National Bureau of Standards Monograph 158, entitled Corrosion and Protection of Steel Piles in a Natural Sea Water Protection of Steel Piles in a Natural Sea Water Environment. The monograph describes the first 6 to 8 years of a 15-year program for evaluating the ability of a variety of coatings and cathodic protection systems to protect offshore steel piles at Dam Neck, VA. protect offshore steel piles at Dam Neck, VA. Materials and Environment

Steel beams were chosen for exposure because of their strength and availability. The 8- × 8-in. (20 × 20-cm) mild steel H-piles used are 35 ft (10.7 m) long and weigh 48 lbm/ft (66.4 kg/m) or almost 1 ton (907 kg) each.Six coatings on H-piles are described here, although the entire program includes 23 different types of protection on H-piles and pipe piles. These six coatings protection on H-piles and pipe piles. These six coatings are a metal-pigmented coating, and five nonmetallic coatings on a zinc-rich primer (Table 1). Several bare piles are included in the program to serve as controls and piles are included in the program to serve as controls and to provide comparison with protected piles.The Dam Neck site was chosen for three important reasons. First, it is located midway between the most northern and southern points of the eastern U.S. shore. Thus, the climate is temperate with a mean water temperature of 57.9 degrees F (14.4 degrees C), ranging from 33.8 to 82.4 degrees F (1.0 to 28 degrees C). Mean salinity is 26.8 ppt. Second, it is an unprotected site open to the ocean. Wave and surf action found at this location is strong, causing sand to be lifted from the bottom and carried in suspension. The impingement of these sand particles on obstacles near the sand bottom leads to a region of sand abrasion, the erosion zone, which is detrimental to practically any coating. And third, there is a well-developed beach area from which the ocean site can be reached.The piles are exposed to three major zones atmospheric, immersion, and imbedded. These can be subdivided further into smaller regions, as illustrated in Fig. 1. From the standpoint of corrosion and coating deterioration, the least aggressive of the zones is that portion of the pile buried in the sand, the imbedded zone. portion of the pile buried in the sand, the imbedded zone. Above this zone we find the immersed zone, composed of the fouling zone, where a multitude of life forms exist, and the very aggressive erosion zone already mentioned. The location of the erosion zone changes constantly as the level of sand shifts with storms, waves, and cross currents. Fig. 2 is a plot of the changing sand bottom with time. The section of piles that extends out of the water is the atmospheric zone and the splash zone.

JPT

P. 1035