ROV Deployed
Ultrasonic Thickness Gauging System

Cygnus Instruments is a provider of subsea ultrasonic thickness gauges for a diver deployment. The Cygnus-1 gauge has been the industry standard for 10 years or more. It was natural that the industry should expect Cygnus to develop a gauge for ROV deployment. W/ the original MK1 system being launched in 1992, Cygnus has now completed the development of the MK3 system, a completed off the shelf tool. The device, like all Cygnus products, uses multiple echo measuring techniques to obtain fast, accurate and repeatable thickness readings. Only minimum surface preparation is required and coatings do not have to be removed (see below). Fast measurement and ease of mobilization and set-up means that inspection time and costs are kept to a minimum.

The Equipment

The gauging unit itself consists of an electronic module housed in a pressure and water proof vessel made of high grade engineering plastic or stainless steel. The two versions are good to 500 meters (weight 2.75 lb) and 3000 meters (weight 8.8 lbs) respectively. Both are 2.75 " in diameter and 9.3" long. The module powers the ultrasonic transducer (probe) and processes signals from it. The probe is connected to the gauging modules w/ 16 ft of special underwater coaxial cable. The probe / cable assembly simply screws into the main body and becomes integral w/ it for operation. Other electrical connections for power and data communications are provided via an industry standard four-way underwater mateable connector. This is connected in turn to the vehicle umbilical. The system requires a DC power supply of 9-24 V and draws a maximum of 150 mA. The power supply uses two of the four conductors, the remaining two conductors are used for serial communications to the surface. The readings are transmitted to the surface using standard RS485 signals, to a maximum range of 13000 feet. At the surface, the data is converted to RS232 and the readings displayed on a computer screen by Windows™ (Versions 3.11, 95, 98, or NT) software supplied w/ the system. This program will also allow the logging of the readings against date and time along w/ a simple commentary. Alternatively, the RS485 data from the gauging module could be integrated into the vehicle telemetry and control system to allow measurements to be viewed topside.

Measurement Technique

As previously stated, the Cygnus system uses the multiple echo method to obtain the thickness reading. This method measures the time of flight of three successive echoes from within the metal, not the usual single echo most other manufacturers employ. Cygnus also employs an error checking technique to ensure that only true backwall echoes are used for measurement, reducing the chance of erroneous readings being obtained from internal or contact imperfections. The metal surface does not need to be ground out, although surface growth or adhesion needs to be removed. Measuring in this manner means that the thickness of any intervening layer, such as a coating, is not included or "added" to the thickness. The system will measure through a significant thickness of coating, up to about 0.25", providing it is well adhered to the base material. This allows the system to measure through a short water path (up to 0.2"). The probe does not have to touch the metal surface to get a reading, which allows for easier vehicle manipulation. The Cygnus probe is of the single crystal type and does not have to be carefully aligned on a tubular section as does the twin crystal type. The probe face is covered w/ a soft compliant membrane, again making manipulation easier.

Calibration

The system is calibrated on the metal to be measured remotely from the display software. This program also allows the readings to be displayed in other units (inch or metric), meaning the module need not be retrieved or opened to change material settings. The program also contains a list of material velocities allowing automatic calibration. The system covers a range of materials w/ velocities from 2500 to 7000 m / s.

Accuracy, Resolution and Range

The system will provide an accuracy of +/- 0.04" across its measuring range of 0.04 to 8.0". The unit provides a measuring resolution of 0.1 mm or 0.005" depending on the units in use.

Options

Should an operator wish to engineer the electronics into his own enclosure or rack, Cygnus will provide the system "bare" along w/ the support necessary. The system can also be provided w/ a measuring accuracy and resolution of 0.05mm or 0.002".

Ordering Information

Cygnus Instruments Main Index | NDT Equipment Main Index

Home | Product Index | Email

© 2003 Aqua Air Industries, Inc. - All Rights Reserved

AQUA AIR INDUSTRIES, INC.
639 Manhattan Blvd.
Harvey, Louisiana 70058 USA