INTRODUCTION 



The development of deep diving vehicles which can stay submerged 

 for long periods of time has focused attention on the deep ocean as an 

 operating environment. This has created a need for information concern- 

 ing the behavior of common materials of construction as well as newly 

 developed materials with promising potentials, at depths in the oceans. 



Since 1959 the Naval Civil Engineering Laboratory has been develop- 

 ing the technology necessary for designing, constructing, inspecting 

 and maintaining structures and fixed equipment on the ocean floor. A 

 part of this program is to determine the effects of deep ocean environ- 

 ments on the corrosion of metals and alloys. 



In order to determine the effects of deep ocean environments on 

 the corrosion of metals and alloys , a Submersible Test Unit (STU) was 

 designed, on which many test specimens can be mounted. A STU unit is 

 shown in the inset of Figure 1. 



The test sites for the deep ocean exposures are shown in Figure 1, 

 and their specific geographical locations are given in Table 1. The 

 complete oceanographic data at these sites, obtained from NCEL cruises 

 between 1961 and 1967, are summarized in Figure 2. Initially, it was 

 decided to utilize the site at the 6,000-foot depth (STU 1-1, 2, 3 and 

 4) . Because of the minimum oxygen concentration zone found between the 

 2,000- and 3,000-foot depths during the early oceanographic cruises, 

 it was decided to establish a second site (STU II-l and II-2) at a 

 nominal depth of 2,500 feet. For comparative purposes the surface water 

 Site V was established. Even though the actual depths are shown in the 

 tables, the nominal depths of 6,000 and 2,500 feet are used throughout 

 the text. 



A summary of the characteristics of the waters 10 feet above the 

 bottom sediments at the two deep ocean exposure sites and 5 feet below 

 the surface at the surface exposure site is given in Table 1. 



Sources of information pertaining to the biological characteristics 

 of the bottom sediments, biological deterioration of materials, detailed 

 oceanographic data, and construction, emplacement and retrieval of STU 

 structures are given in Reference 1. Bottom sediments as used herein 

 means from the water-mud interface to a mud depth of about 6 inches. 



The procedures for the preparation of the specimens for exposure 

 and for evaluating them after exposure are described in Reference 2. 



Previous reports pertaining to the performance of materials in the 

 deep ocean environments are given in References 1 through 11. 



This report presents a discussion of the results of the corrosion 

 of stainless steels obtained for the seven exposure periods shown in 

 Table 1. 



