to the initial reference). Where damage is indicated, the diver provides 

 close visual observations concerning the type and location of damage, 

 eccentricity of voids and other pertinent information. These observa- 

 tions are relayed to the surface technician through a telephone link. 



Several of the inspected pilings were removed, sectioned, and 

 crushed to compare inspection results to actual cross-sectional area and 

 remaining strength. This study was designed to: evaluate the inspection 

 test results obtained with the ultrasonic test equipment; compare the 

 ultrasonic inspection results with visual inspection results; and compare 

 ultrasonic and visual inspection results with established accuracy re- 

 quirements. Reference 12 presents a detailed description of the capabil- 

 ities demonstration and discussion of the results. A brief summary of 

 the results are stated as follows: 



• The Agi and Associates ultrasonic inspection equipment can detect 

 both external and internal timber damage. 



• The ultrasonic inspection overestimated the actual damage in San 

 Diego by an average of 16% and in Hawaii by 18%. Visual inspection of 

 the same piles in Hawaii underestimated damage by 13%. 



• The variance for both the visual and ultrasonic inspections was 

 very high. The standard deviation ranged from 12.1 to a high of 21.9 

 for the ultrasonic inspections and 13.3 to 16.3 for the visual inspec- 

 tion results. Since the variance is directly related to the precision 

 of the measurement of cross-sectional area for any single pile it should 

 be much lower to meet the accuracy requirement of 20 to 25% given in 

 Reference 1 . For 95% of the measurements to fall within the accuracy 

 specification, the standard deviation associated with the measurement of 

 cross sectional area must be approximately 6% or less. From this stand- 

 point, neither inspection technique meets the inspection criteria defined 

 in Reference 1. 



NCEL Ultrasonic Laboratory Testing 



The reason for pursuing indirect ultrasonic testing at NCEL was 

 based on three points: 



• Previous ultrasonic tests conducted at NCEL (Ref 7) showed that 

 although a consistent correlation between the ultrasonic signal and the 

 wood specimen condition could not be identified, alternative ultrasonic 

 parameters had not yet been investigated. Further study was warranted. 



• The results from the SWRI contract indicated that indirect ultra- 

 sonic testing is a feasible inspection technique. Positive results were 

 achieved when the RMS of the ultrasonic signal was compared to the amount 

 of wood lost. The signal RMS consistently decreased with an increase in 

 wood damage. 



• The Agi and Associates ultrasonic test demonstration proved that 

 ultrasonic equipment is not just a potential technique; it has been 

 satisfying a current need. Although the accuracy is less than the pre- 

 determined requirement, ultrasonic inspection reveals information about 

 the interior, rather than only the exterior, of a timber pile, as with 

 visual inspection. 



16 



