CONCLUSIONS 



Many important deterioration protection principles were incorporated 

 in the design of the ECHO tower of the Azores Fixed Acoustic Range. In 

 critical areas such as the steering carriage shaft seals, materials known 

 to be immune to corrosion were used. In non-critical areas materials 

 subject to only uniform attack were used and these materials were protected 

 over the majority of their surfaces by the use of protective coatings, 

 especially by the use of zinc rich primers. Such primers afford galvanic 

 protection to the underlying steel should the barrier film of the topcoats 

 be ruptured. For components such as the gas generator valves and the 

 carriage lock jacks and keys, where their long term corrosion resistance 

 was insignificant, materials selection was based upon other considerations. 



In a few areas, however, considerable improvement in the long term 

 reliability of the tower could be realized. 



The use of sealants to prevent corrosion of materials subject to 

 crevice corrosion is not reliable. Such a system was used on the fasteners 

 used to attach the cable conduit to the main column. Only one fastener 

 was removed from this area and it had corroded to a depth of .005" due 

 to crevice corrosion. This attack was not critical, however, as the 

 number of fasteners used would allow the failure of many before the conduit 

 attachment would be jeopardized. 



Another area of potential failure was the attack noted on the antennas. 

 Pits on the 1/16" thick material of high frequency compliant tubes had 

 progressed to near penetration in a few areas. Such penetration would 

 cause the loss of gas which would result in antenna failure. All the pits 

 noted in the antennas were at areas of paint repair where no zinc rich 

 primer was applied. These pits were considered to be the most severe attack 

 noted on the tower in terms of system reliability. All other attack noted 

 was insignificant in terms of system reliability when compared with the 

 pits on the antennas. 



The additional lifetime of the tower when reemplaced depends almost 

 entirely on the attack on the antennas. If the pits already present 

 reinitiate and penetrate still further the useful additional life of the 

 tower may be as little as one year. However, if the recoating of these 

 areas is successful and corrosion occurs at other areas the additional 

 useful lifetime of the tower will depend on the thickness of the material 

 on the antenna attacked. The 1/16" thick material of the high frequency 

 antenna could last as long as five years and the others proportionately 

 longer. 



RECOMMENDATIONS 



These recommendations apply to both the modification of the existing 

 towers in the event they are recovered and subsequently reemplaced and to 

 the building of other similar structures. 



