IRIS

IRIS is an Internal Rotating Inspection System with which the remaining wall thickness of tubes can be measured. IRIS can be applied on both ferrous and non-ferrous tube materials. IRIS is more accurate than the other tube inspection techniques and it has the advantage of presenting information about the geometry of the defect. Local defects and wall-loss on the inside as well as on the outside of a tube can be accurately measured. Defects under support plates can be easily detected and quantified without any disturbance of the signal. Biggest drawbacks of IRIS are the inspection speed and the necessity for the tubes to be very clean. Approximately 70 tubes, with a standard 6 meter length, can be done on a first inspection day. Speed can go up to as many as 100 tubes on additional inspection days. The thorough cleaning and the low inspection speed will cause high inspection cost for IRIS. Therefore IRIS will often be used as a verification tool in combination with one of the other techniques...

IRIS INSPECTION OF TUBES

Internal Rotary Inspection System (IRIS)
IRIS is a technique used for the inspection of tubes in e.g. heat exchangers, boilers and airfin coolers. IRIS can be applied on both ferrous and non-ferrous materials. With IRIS the remaining wall thickness of tubes can be accurately measured. IRIS is more accurate than other tube inspection techniques and has the advantage of presenting information about the geometry of defects. Local defects and wall-loss on both sides of the tube can be accurately measured. Defects under support plates can be measured without any limitations.

Theory
The probe used in IRIS examination is made up of a centering device, an ultrasound transducer and a rotating mirror. An ultrasound pulse will be generated in the transducer that is mounted in axial direction. A 45 degree rotating mirror in the probe will guide the sound bundle towards the tube wall. An ultrasound reflection (echo) will take place at the inner and at the outer wall of the tube. These echoes are reflected back and processed by the equipment. The time between these two echoes represents the wall thickness of the tube. Knowing the sound velocity in the material under test, an accompanying wall thickness can be calculated. Water is used rotate the probe mirror and is also needed as a couplant between the transducer and the tube wall. A calibration standard of the same material and dimensions as the tubes to be examined is used to check the
IRIS system response.

After an inspection an “on-site” report detailing the condition of each tube will be presented to the client.



Equipment
For IRIS inspection Dacon Inspection uses the IRIS Ultima IV tester. This tool is designed for detailed inspection of tubes in the diameter range from 1/2” to 6”. The IRIS signals are presented on a portable computer and all inspection data is automatically stored to hard disc. The equipment operates on 220 V, 50 Hz. The equipment requires water as a couplant.



Overview of possibilities and limitations of IRIS

• This is a rotating ultra sound inspection method to measure the wall thickness of tubes. The technique can be applied to ferrous and non-ferrous tubes (e.g. carbon steel and Stainless steel ). The method can also be applied on finned tubes.
• The data obtained with this inspection is presented in such way that it is possible to determine depth and geometry of defects.
• It’s very accurate for measuring both local internal as external defects and wall thicknesses (pits with a diameter of 2 mm and bigger can be detected). It's possible to distinguish between internal and external defects.
• Wall thicknesses smaller than 0.8 mm cannot be measured reliably.
• The examination is not being influenced by changing material characteristics like conductivity and permeability. Changes in these factors can cause false indications when using electromagnetic testing methods.
• Defects under support plates can be detected and sized.
• Bends cannot be examined, but it is possible to pass bends in bigger (boiler) tubes to inspect the straight ends after the bends.
• Speed: to scan an entire tube wall with maximum sensitivity, pull speed will be around 5 cm/sec.
• This technique is often used as a tool to verify RFT and PSEC results and to get additional information on the geometry of defects.
• Tubes need to be very clean as dirt my cause loss of signal.

Remark: Named values concerning sensitivity and accuracy have been generalised. In particular sensitivity is very 
dependend on the cleanliness of the tubes.

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