INTRODUCTION 



The Naval Civil Engineering Laboratory (NCEL) previously conducted 

 a study on nondestructive evaluation (NDE) equipment for wire rope 

 inspection", which compared conventional equipment (individual AC/DC 

 units) to that of newly developed equipment (a unitized AC/DC unit, the 

 Magnograph) . The operational features of the two types of equipment 

 were reviewed, and a limited test program was conducted to compare the 

 results. The report recommended that the Magnograph equipment be pur- 

 chased for Navy applications because it was found to be more versatile 

 than the AC/DC units; e.g., data were recorded simultaneously on strip 

 chart paper for both local fault (LF) defects and loss of metallic area 

 (LMA) recordings and the equipment could be operated at slow speeds, to 

 fpm, and still detect LF and LMA data. This report presents results 

 of a test and evaluation program conducted on the Magnograph unit before 

 Navy field activities acquire the units and start field inspection 

 programs. 



Preliminary Testing With Broken Wire 



The original two objectives of the program were: to define broken 

 wire signals for producing a pictorial defect catalog and to determine 

 the accuracy of the LMA data. The results would assist inspectors in 

 interpreting data from field tests on wire rope. As testing progressed, 

 it became clear that a defect catalog could not be developed. The LMA 

 readings were found to be outside the manufacturer's accuracy specifica- 

 tions. A method for obtaining accurate LMA readings was developed, 

 however, and is available to inspectors who take special effort to 

 calibrate the equipment. The new calibration method is presented in 

 this report. 



The interpretation of LF data on broken wires requires experience 

 to understand both gross and subtle meanings. Often signals of back- 

 ground noise are difficult to distinguish from signals of broken wires. 

 The equipment sometimes does not give all the answers on broken wires; 

 the data sometimes only indicates the general condition of the wire 

 rope, especially if the wire rope is heavily worn or corroded. Some 

 broken wires give signals that indicate definite breaks, but other 

 broken wires give signals difficult to distinguish from background 

 noise. In the latter case, broken wires can go undetected. 



One of the more important findings of this program is that every 

 broken wire does not produce an obvious broken wire signal."" Broken 

 wires having a small gap between the broken ends produce only small 



"Civil Engineering Laboratory. Technical Note N-1594: Nondestructive 

 testing equipment for wire rope, by H. H. Haynes and L. D. Underbakke; 

 Port Hueneme, Calif., Oct 1980. 

 ^'^'='This finding also applies to the conventional DC-type equipment as well 

 as to the Magnograph equipment. 



