=New equipmen

Incorporating the latest ultrasonic technology, the HFD-2 flaw detector from the National NDT Centre operates with up to 64 channels

busy in the field.

The following parameters are under computer control and can be separately adjusted for each multiplexed probe: pulse voltage, pulse width, gain, bandwidth, digitization rate, rectification, DAC law and gates. Up to 64 DAC law curves can be pre-stored for providing the appropriate swept gain. The digitized

signals can be averaged to improve the signal-to-noise of weak signals (e.g. diffraction signals). For each probe up to five overlapping gates can be specified. A general-purpose three-axis motor controller/encoder is available for automated manipulator operation.

NNDTC, Harwell Laboratory, Oxfordshire OXI 10RA, UK

Bulk storage tank floor inspection service Inspection specialist TASC (Sonomatic) has launched a service to aid in the assessment of storage tank floor condition. The company has undertaken several petrochemical storage tank inspections for Esso in Eu~ope, and is offering a competitive service to other clients in the oil, gas and chemicals industries worldwide.

Traditionally, the condition of tank floors has been assessed

by examining floor plates cut out at random, or by spot ultrasonic thickness measurement. Both techniques assess only a small percentage of the floor area, and as corrosion of tank floors is an isolated, random occurrence, these procedures are unreliable, even when advanced statistical sampling methods are used.

The new service provides more than 95% coverage of tank

floors and indicates the results of the inspection in real time. The equipment used is a magnetic f lux leakage system which has been designed to detect corrosion in the 6 mm and 10 mm thick carbon steel sheets that make up the bottom of large storage tanks with a diameter of 6 m or more.

The flux leakage technique works by flooding the tank floor plate with magnetic flux generated by electromagnets. Areas of corrosion represent discontinuities in the magnetic circuit through the tank floor. These cause flux leakage, which is detected by a separate probe.

The system consists of a rotary scan unit which is rolled over the plates, a power supply for the electromagnets, and data-processing instrumentation to display the results of the inspection. A remote monitor allows the operator to monitor the output in real time.

The sensitivity of the system is such that it can generally detect the presence of a 3 mm diameter flat-bottom hole, 20% deep, on the far side of the plate.

Sonomatic also offers a further, complementary inspection service. Areas found to be thin can be examined in more detail using its See-Scan system. A manual operator can use this to generate a colour-graphic map of the suspect area in the form of a plan elevation, or C-scan. Different residual plate thicknesses are indicated by different colours, superimposed on a video image of the area under test. There is no need for a complex manipulator system. A six-colour printer allows instant hard-copy reporting if required.

Sonomatic Ltd, 20 Rivington Court, Hardwick Grange, Woolston, Warrington WA 1 4RT, UK

278 N DT & E International October 1991