The condenser consists of 40846 welded titanium tubes which are installed into three nests. The diameter of a titanium tube is 25.4 mm with wall thickness of 0.71 mm and length of 16000 mm.

The four frequency eddy current equipment has four differential and four absolute signal channels for measuring eddy current signals from a detection probe. From them two mixing eddy current signals can be produced. Two strip charts (X and Y components) of a frequency and four kinds of eddy current impedance planes can be simultaneously displayed on a screen of a computer terminal to assist the analysis of a defect eddy signals selected among four frequency differential and absolute channels.

Frequency characteristics of a detection probe and selection of detection frequencies applied to the detection probe are very important for tubing eddy examination.

The central frequency and frequency band of the probe shall induce maximum eddy signal for a standard calibration tube defects, and also make it possible to locate the eddy current signal induced by a kind of tube supporting plates and defects in the standard calibration tube into opposite quadrant on the quadrantal plane coordinates. The central frequency of probes is designed at 300 kHz, and its frequency band is about 50 kHz to 600 kHz. 400 kHz and 307 kHz for defects detection in tubes. 80 to 120 kHz with 400 kHz and 307 kHz for producing optimal mixing signals are selected to detect defects and wears of tubes under supporting plates. Because the diameter of welded titanium tubes varies slightly round its average diameter at different length, measurements of absolute eddy current signals of wears under supporting plates become difficult. For this a larger ratio of eddy current signal to noise and good mixing frequency selection are necessary if no special restraint method for this slight tube diameter change does not be used.

GNPS has two units called as unit 1 and unit 2. During the second ISI of unit 2, 30% tubes of the total welded titanium tubes in the condenser of unit 2 will be examined.