ACOUSTIC EMISSION & NDT SCIENTIFIC PUBLICATIONS

 

Tube Scan: Rotating Internal Scanner for Ultrasonic Tube Inspection

 

4^th National Conference of H.S.N.T. and 2^nd Balkan Conference of BSNDT Athens, November 2, 2002

R. Kazares and A. Anastasopoulos

 

The system has been used in several applications for the industry and ha proved reliable and accurate when inspecting tubes. C-Scan results offer and immediate comparison between tubes and thus decisions for maintenance-replacement or repair can be made quickly and be targeted to the problematic areas with good confidence of the outcome.

With such systems large-scale tube inspection has been made possible and economical for the industry, thus increasing plant efficiency and improving maintenance-replacement or repair decisions.

Boiler and Heat-Exchanger tubes are exposed to an adverse operating environment due to the fluid in conjunction with pressures and temperature in such equipment. In many cases corrosion and/or erosion play an important role in the life of such tubes. In other cases the operating conditions lead to flaw development in the tubes’ material. In addition, failure of one or more tubes in such equipment may cause significant problems to operations. The need for inspection has been recognized but the inspection itself proves difficult and is restricted to simple methods.

Ultrasonic Non-Destructive Inspection (NDI) has been widely used for corrosion/erosion and flaw detection and assessment of nearly all metallic structures. Their application to tubes has proved difficult, though, due to the restricted access to these equipment and due to the large surface to be inspected. Boiler and Heat-Exchanger tubes are in a confined space and they are usually packed together so access is restricted. Their size (diameter) and their large number make it difficult to inspect by manual techniques.

Advances in the field of Automated Ultrasonic Testing (AUT) have given a tool that can be utilized for fast large-scale tube tests. Several problems had to be addressed in order to achieve practical application systems.

The present work outlines the basic operating principles of Rotating-Mirror Internal Tube Scanner - TubeScanä developed specifically to address the problem of boiler and heat-exchanger tube ultrasonic inspection.

TubeScan, is a fully automated, TurnKey Ultrasonic Inspection System, designed to perform high-speed ultrasonic C-Scan imaging of small to medium diameter tubes. Typical applications such as inspection of Boiler Tubes, Heat Exchangers and Coolers are presented and advantages and limitations of inspection are discussed.

TubeScan is based on a PC based ultrasonic system with high resolution digital ultrasonic pulser-receiver (PR) and analog to digital converter (AD) board. Internal encoders are used to move the probe inside the tube and track the motion with high accuracy.

The easiest access to the surface of tubes is through their inside diameter. TubeScan uses a flexible stainless steel tube to advance the UT probe inside the tube using motors that are controlled from internal PC encoder board. Water is used for acoustically coupling the probe and the tube. Mirrors are used to reflect the beam at right angles to the tubes surface so that corrosion/erosion effects can be observed in the form of a C-Scan. The mirrors can be used to deflect the beam at intermediate angles so that the equipment can be used for flaw detection in the tubes’ material.