To make protective effect of coatings under practical conditions clear, four kinds of paints and three kinds of paints applying along with coating materials, such as glass or vinyl cloth, were applied to the portion above low water level of steel pipe piles of -10m quay wall at Chiba harbour and after 3.7 years the survey of coatings was done and the (following) results were obtained.
　1) It was approved that in the case of steel pipe piles coated with good quality tar-epoxy paints independently whose film thicknesses were several hundreds micron or more, damage of the paints resulting from passing through by barnacle was nearly checked.
　2) It was found that in the case of steel pipe piles coated with paints applying along with coating materials, such as glass or vinyl cloths, the protective effect of the coatings depended nearly on the kind of paint, and for instance, some tar system paints showed more good protective effect than an asphalt system paint.
　3) In the range of +2.7m to +2.2m, where was above high water level and baranacle couldn't reach, in tar-epoxy paints, tar system or asphalt system paints applying along with coating materials, with the exception of chlorinated rubber paint, damages of coatings damages of coatings didn't nearly occured.
　4) In driving long coated steel pipe piles into sea water,coatings of 20 percent steel pipe piles got damaged.