sections. It was found to be practical to protect 'H' piles effectively 

 simply by encasing them in tubular shields in the mud line re":ion. here 

 heavjr 'H ' piae sections were eroded through in less than 20 years, tubular 

 shields only 3/l6 inch thick were able to survive. In the practical in- 

 stallation the space between the tubular shields and the 'H ' pj.les was 

 filled with concrete grouting. In some instances, also, tubular piling 

 was given satisfactory protection by a silica sand reinforced somastic 

 coating vrhich also exhibited good resistance to sand scouring. 



Since the steel in the tubular shields was inherently no more resistant 

 to erosion then the steel in the 'II' piles, the better performance of the 

 tubes must have been due primarily to their more favorable shape. Evidently, 

 the pattern of flow of water and suspended sand around a smooth cylinder 

 is accompanied by much less severe erosive forces than are associated with 

 the impact of currents and eddies on the 'H' pile shape. 



'.Phis su'5;gests that this favorable property of tubular piles should be given 

 considerable weight in choosing such a shape rather than an 'H' section 

 for piles to be driven vdiere sand scouring may be anticipated. It seems 

 likely also that the tubular shape vrould have an additional mechanical 

 advantage because of the lower stresses resulting from the lesser impact 

 of waves. 



In any event, in the light of these experiences, it would be vrell to pro- 

 vide 'K ' piles v.'ith tubular shields to prevent excessive wastage by sand 

 scouring where this may be expected to occur. 



Zone 3 - Below Low Tide 



Corrosion below low tide is not likely to be a maj or factor in determining 

 the life of a steel nile. As measured by weight loss, the rate of attack 

 is not likely to exceed 0,005 inch per year - local attack by pitting may 

 reach a rnaximuJii of three times this rate over an extended period. In 

 tropical ¥/ater3 where calcareous deposits are likely to coat the steel, 

 even lower rates of attack may be anticipated. 



.'hen some steel piles were being removed fromx ah offshore structure on 

 the Pacific Coast recently E. Ilartinen of the Signal Oil & Gas Company 

 observed very peculiar and severe corrosion of surfaces near the bottom. 

 This took the form of keep hemispherical pockets, each of which was occupied 

 by a living sea urchin of the species Strongylocentrotus purpuratus. The 

 surface of the steel belov/ these organisms vras bright as though it had been 

 s'lfferiH;!^ continuous active cox^rosion, possibly as a result of the action 

 of the sea urchin in keeping the metal abraded slightly so that no protective 

 corrosion product films could develop. Presumablj^ this T-zould require the 

 activity of a series of successive inliabitants of the pockets Y/ith the size 

 of the occupying organism increasing with size of the pocket. Apparently 

 this association of sea urcliins with corrosion is rare, since there are no 

 previous reports of similar occurrences on record. 



E - 3 



