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| Factors Influencing Test Methods | ||||||||||
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Common Defects Detected | |||||||||
| Generally, for tube applications that require high throughput speeds, eddy current is the preferred method to detect small, short, incomplete welds,and some subsurface cracks in carbon steel or non ferrous tube. For full body tests, including the detection of long, continuous defects such as incomplete seam welds in tube, and inclusions, voids or cavities, ultrasonic test systems are recommended. Flux leakage systems are available to accurately detect longitudinal and transverse surface defects on the OD and ID of heavy-wall magnetic tubing. | ||||||||||
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The picture above shows a short pinhole flaw that was detected by eddy current, but was difficult to detect using ultrasonic tests.
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Weld Types | |||||||||
| The process of ERW and Induction welding is preferred for most carbon and alloy steel. Defects that may arise include all of those previously mentioned. TIG welding is a slow process usually used for stainless steel or titanium. Incomplete ID weld defects are a common concern in this process. Laser welding is a much faster process used for stainless steel, titanium, duplex and nickel alloys. Typical defects include very short pinholes, and long continuous ID defects such as incomplete or miss-match welds. | ||||||||||
| This picture above shows a cross section of a tube wall with a long, continuous poor ID weld that was detected by ultrasonic methods, but not by eddy current. | ||||||||||
| Eddy Current Instrumentation | ||||||||||
| MAC eddy current instrumentation includes the MultiMac®, MAC 400 and Minimac® equipments. Installations can be in-line, or off-line. Eddy current technology is most effective on tube with wall thickness up to 3/8″ (9.5 mm) and diameters up to 8.85″ (225 mm). Defects detected by eddy current test methods are short OD and ID, some subsurface, laps, open welds, and other weldline defects in magnetic and non-magnetic tube. | ||||||||||
| MutliMac® | Mac 400 | |||||||||
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The MAC 400 is a Windows® based tester that displays test results and settings in large onscreen windows. An optional touch screen is available. Up to 4 independent test channels can be used for applications where multiple probes detect different defect types, or where multiple sensors are in a single segmented encircling coil, or for marking and sorting on up to 4 weld lines. |
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| Minimac | ||||||||||
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The Minimac® Mac 40 is a low cost, single channel, Windows® based tester.It is designed primarily to operate on continuous product on a production line. The unit is controlled with a keyboard and separate monitor supplied by the customer or by MAC as an option. | |||||||||
| Coil Platforms | ||||||||||
| Encircling or segmented test coils (for higher sensitivity), can handle magnetic and non-magnetic tube up to 9” (228mm) diameter. Sector or tangent coils are available in a wide range of custom sizes. | ||||||||||
 CP10 with encircling coil fortesting non-magnetic material |
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CP65 with encircling coil and |
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| Standard encircling coils are designed to inspect non magnetic material such as smaller diameter copper and aluminum tube. For light wall stainless and carbon steel with minimal permeability variations, permanent magnet test coils can be used. | Tangent (sector) coils are used on some weld lines, where threading the material through a coil is difficult and only the weld zone area needs testing. They are also used on larger diameter heavier wall thickness tube where encircling coils are not practical. Because they cover a limited test area of the tube under inspection, an improved signal-to-noise ratio may result. Sector coil platforms with or without DC saturation are available. | For most carbon steel and certain grades of stainless, direct current saturation is required to reduce permeability variations that can interfere with the eddy current test. MAC encircling or sector DC saturation coil platforms, air or water cooled, provide the required saturation for the test. | ||||||||
| Ultrasonic Instrumentation (UT) | ||||||||||
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For more demanding test specifications, MAC provides ultrasonic FD-5 Electronics The FD-5 is a computer based ultrasonic inspection instrument designed for in-line flaw detection, and thickness and ID/OD diameter measuring. Up to 32 channels can be installed in a single system and more channels may be used with additional units. The FD-5 is housed in an environmental cabinet. The FD-5 software allows the customer to configure individual channels to detect dimensional variations or flaws. The software package comes with multi-channel A-scan viewer/ recorder, test signal recorder, end suppression, tracking system, strip chart viewer, production logging, data compression, storage, color printing, and remote network interface. |
Echomac FD5 Setup A-Scan screenDisplays a setup for channel 1 with a gate interface and 4 gate thresholds. Date, time, part number, length, throughput speed, and file storage location are also shown. |
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ECHOMAC® Rotaries MAC ECHOMAC® rotaries house the transducers and couplant and can handle material up to 220mm (8.66″) diameter. For tests on some small diameter tube, generally up to 75mm (3″), MAC UT rotaries can be installed on the weld line where they can operate at production line speeds. For larger diameters, MAC has worked with Reliant Technologies to provide mechanical handling, fixturing, data acquisition, and irrigated transducer shoes that position the transducers and maintain coupling with the test material. MAC also has developed systems using alternative coupling methods, including bubblers and squirters. MAC FD-5 electronics can also be used to upgrade customer’s existing immersion tank systems. |
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| Typical defect capabilities include longitudinal and transverse, short or continuous, and better ability than eddy current test methods to detect ID stringers, inclusions, incomplete weld, hooks, cracks, and tapered defects. Throughput speeds depend on the length of the notch, and diameter, length, and wall thickness of the tube. | ||||||||||
| Flux Leakage Instrumentation | ||||||||||
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MAC’s Rotoflux® flux leakage test systems accurately detect longitudinal and transverse OD and ID defects as small as 5% of the wall in annealed heavy wall magnetic tubular products including oil country tubular goods to meet API specifications. In line seam annealing makes physical properties more uniform and allows for precise test results. Recent MAC systems have featured 24channels for longitudinal defect detection and 48 for transverse defect detection. Rotoflux® The transverse and longitudinal Rotoflux® tests pipes from 2.5” (63.5mm) to 16” (406.4mm) in diameter at greater throughput speeds and lower running costs than many NDT systems. The electronics are capable of differentiating between ID and OD defects, using a unique multi probe feature which allows for convenient operation. A flux measurement circuit is included to indicate whether the test piece is properly saturated. The detection of longitudinal notches can be as short as 0.5” (12.7mm) and through holes as small as 0.032” (0.8mm). Longitudinal test speeds range from 0-700 fpm (213m/m) and transverse speeds vary from 20-500 fpm (6-152m/m) Smaller diameters may be accommodated. |
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| For many applications, the optimum solution is a combined system that utilizes both eddy current and ultrasonic test instruments to take advantage of the relative strengths of each technology. | ||||||||||
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| MAC automated test systems for welded tube incorporate comprehensive computer controls, eddy current and/or ultrasonic test electronics and test sensors, pinch stands or guides, and accessory equipment such as demagnetizers, markers, conveyors etc. as needed. These components are mounted on V roll or Constant Center test benches. | ||||||||||
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A Conductor computer system supervises and executes communication with the bench. The system is Windows® based and comes with a rack mounted monitor. This is the operator console where setup and control is performed with the use of a keyboard and mouse. The Conductor software package controls the test bench, the end suppression, the dual pinches, sorting and marking. The Conductor also calculates all compensations required to 
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Two Bench Types – V Roll and Triple Bench. The V roll consists of motorized dual pinch roll stands. These pinches along with the testers and motors are The MAC Triple Bench is a guiding and driving unit that centers the tubes through the test units. The bench features dual leading and trailing triple guides to guarantee a controlled entrance and exit from the test stations. Each triple pinch has a separate AC motor. A slide mechanism is provided to allow for the test heads to be moved off-line for setup and maintenance. |
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Some weldline cracks, such as this one shown above, may be detected by both eddy current and ultrasonic equipment.
Factors that influence system selection include the capabilities and limitations of each technology, as well as the diameter, wall thickness, tube condition, and throughput speed of the product under test. Where the test is applied in the manufacturing cycle also influences the choice of method and apparatus. This can range from tests limited to the heat affected zone on the weld mill with perhaps an in-line anneal, to full body inspection of cut lengths after drawing and annealing or other heat treating. Each test method has inherent capabilities and limitations that are different.
A water system is included with Ultrasonic inspection systems. It is comprised of a chiller for maintaining couplant temperature within an acceptable range, filters for removing contaminants and pumps and reservoirs for moving the water through the system.