Eddy Current, Ultrasonic or Flux Leakage techniques can be used to inspect welded, extruded, and seamless tubing. The choice depends on the nonconforming conditions you wish to detect, the size, including wall thickness, and the characteristics of the material. MAC instruments can handle a range of metal materials with a uniform cross section, including squares, rectangles, hex and round in cut lengths or continuous production. Carbon steels, stainless alloys, copper, aluminum, titanium and all other non ferrous metals can be inspected. Additional items such as markers, controls, demagnetizers, and components for mounting the encircling or segment test coils, saturation coils, rotaries, and for positioning and driving the material through the test, are combined with the instrumentation to make up a complete test system.
|Typical flaws and conditions that can be detected include:|
|Testing Welded Tube
MAC eddy current test systems are usually the preferred method for welded tube. Test systems can handle carbon steels, stainless alloys, copper, aluminum, titanium and all other non ferrous metals. Eddy current technology is most effective on tube with wall thickness up to 15 mm (5/8″) and is particularly appropriate for finding many of the defects typical of the welding process. Full body tests using an encircling coil can handle tube up to 180 mm (7.2″). Weld zone only tests can be applied to small and large diameters, using sector coils.For more demanding test specifications, MAC provides ultrasonic test systems for full body or weld zone (HAZ heat affected zone) inspection of welded tube. Generally, full body tests are conducted off the weld line on cut lengths. MAC ultrasonic rotaries house the transducers and couplant and can handle material up to 220mm.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, usually testing HAZ only on line, MAC has worked with Reliant Technologies to provide mechanical handling, 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-4 electronics can also be used to upgrade customer’s existing immersion tank systems.
|Testing Seamless Tube
Finished seamless tube typically has heavier walls than welded tube. MAC has eddy current and ultrasonic or flux leakage systems that are appropriate for different types of seamless tube. Eddy current, which tends to be the easiest and most economic technology for example, is best used on smaller wall thickness product. For heavier wall tube and detection of internal defects, ultrasonic or flux leakage (for magnetic material only) would be the preferred method.For either welded or seamless shells that are further processed through cold drawing and where requirements are stringent, ultrasonic methods can be the most appropriate, even on smaller diameters.
|Testing Oil Country Tubular Goods (OCTG)
The method of choice most commonly employed to locate flaws in OCTG is the Flux Leakage test. Convenient and relatively simple, it has the advantage of fast throughput and changeover speeds. Flux leakage systems can also accommodate large diameters that are often difficult to inspect using large ultrasonic machines.MAC systems for OCTG conform to API 5CT or API 5L; which references ASTM E213-04, E-570-04, and ASTM 309-01. Although API 5CT does not recommend a specific NDT method, the L2 level for high strength material calls for establishing a reject level for OD and ID defects at a depth of 5% of the wall thickness or greater. In this case, Ultrasonic Testing proves to be more reliable in distinguishing defects on the tube wall.In thinner wall tube, some API classes may be tested with an Eddy Current System. A drilled through-hole may be used as a reference point for the encircling coil.
|Special Tube Conditions
Upset ends common on some OCTG can be tested with MAC flux leakage and ultrasonic system mechanics which are designed to accommodate the change in outside diameter.Reel to Reel where the throughput speed of the tube varies, MAC test filter settings are adjusted automatically to produce the best indications of the defects. In the copper tube industry, for example, where level winders are used to produce short coils out of long coils for retail sale, the speed varies significantly.
|Ultra Small Diameter
MAC has special eddy current systems that operate at very high frequencies for inspecting ultra small diameter, thin wall tube, frequently used in medical and automotive radiator tube applications, and sheathing for fiber optic cables.
Duplex alloy stainless steel can be successfully tested using MAC eddy current systems that incorporate DC saturation to reduce the magnetic permeability and thereby maximize the defect signal to noise ratio. While duplex alloy is generally considered to be non magnetic and therefore not in need of magnetic saturation, experience in mills producing duplex tube shows the addition of DC saturation substantially improves the test results
|Testing Finned Tube
Mac has developed specialized test coils for inspecting fin tube, including tube with transitional “land” zones, frequently used in heat exchanger applications. Tube with fins or other markings on the inside diameter can also be successfully inspected.
Detecting Flaws and Conditions in Tube and Pipe
Short Surface & Subsurface OD/ID Cracks and Weldline Defects
For detecting typical OD defects such as small, short incomplete welds, inclusions, voids or cavities and some subsurface cracks in carbon steel or non ferrous tube, a standard eddy current instrument such as the MAC 400 or MultiMac® is often selected, with sector or encircling test coils. The choice between sector and encircling coils is usually determined by the wall thickness. The MAC 400 can be supplied with up to four test channels and the MultiMac has up to eight test channels for applications that require greater capability.
For applications where ID, subsurface and internal defects need to be detected in heavier wall tube, the multi channel Echomac FD-4 ultrasonic instrument and rotary transducer assembly, with its unique rotating seal-less water coupling system that permits high throughput speeds is more appropriate. The FD-4 can also be utilized with squirter couplants and existing water immersion systems.
ID Defects in Thin Wall Tube
Generally an ultrasonic test, such as the Echomac FD-4 is the first choice for ID defects. However, some applications, particularly thin wall tubing, can be very successfully handled using eddy current instruments such as the MultiMac® with high frequency and special design test coils. In these cases, careful setup using phase and amplitude thresholds, and other selective circuits can give accurate separation between signals for ID and signals for OD surface defects. This high frequency test is particularly effective for inspecting thin wall tubing for medical and other high performance applications.
Long Continuous Surface Defects
For detecting long, continuous surface defects such as seams and laps in tube, the MultiMac® ,used with rotary test probes, is the most appropriate. By rotating multiple test probes at speeds up to 6000 RPM around the tubing, even relatively short flaws can be reliably detected in many applications, without sacrificing throughput speed.
Short and Long Continuous Surface & Subsurface Defects
For applications where both short and long surface and subsurface defects need to be detected simultaneously, the new MultiMac multi mode eddy current tester would be an excellent choice. With up to 8 channels, each of which can be individually configured for encircling test coils, sector/tangent test coils, or rotating test probes, a comprehensive test is possible. The MultiMac may also, in some instances, be appropriate for detecting ID defects in thin wall tube.
Internal, ID and OD Defects in Heavy Wall Oil Country Goods
Inspecting for defects in heavy wall pipe and tube is best done using flux leakage or ultrasonic techniques. The Rotoflux® tester handles up to 16″ diameter ferrous tube and the Echomac FD-4 FD-4 instrumentation is suitable for ferrous and nonferrous tube up to 6″ diameter. Special handling components are available for difficult conditions such as upset ends.
Internal Longitudinal and Transverse Flaws
For internal longitudinal and transverse, including oblique orientation flaws, and ID defects, ultrasonic inspection techniques are often the best choice. MAC’s multi channel Echomac FD-4 instrumentation and the Echomac rotary transducer assembly, with its unique rotating seal-less water coupling system permits ultrasonic inspection at high throughput speeds. The FD-4 can also be utilized with squirter couplants and existing water immersion systems.
Wall Thickness & ID/OD Measurement
An ultrasonic instrument, such as the Echomac FD-4 provides a separate wall thickness circuit for accurate measurement of tube wall. The FD-4, with its OD measurement capability, can report OD and ID dimensions and ovality, in addition to wall thickness, eccentricity, and wall variation.
Ferrous inclusions in nonferrous tube.
To detect ferrous inclusions such as metal filings from finning tools that are introduced into a tubular product during processing, the MID flux leakage instrumentation is particularly effective. A stable DC magnetic field is established using either a permanent magnet or saturation coil platform and the MID test coil detects changes in the flux field caused by the ferrous inclusion. For finned copper tubing with transitional “land” zones, however, test speeds are currently limited to less than 250 to 300 feet per minute. Titanium tubes without transitional zones, can be inspected for inclusions at higher throughput speeds than copper tube with land zones, however. An MID flux leakage card can be incorporated in MultiMac® eddy current instrumentation.
Short and Long Continuous Defects
For those applications that require the detection of both short and long continuous surface defects, the new MultiMac® tester would be the right choice. The MultiMac with up to 8 test channels, allows simultaneous detection of both types of defects in magnetic or nonmagnetic material.
Alloy and Hardness Detection
Variations in alloy, heat treatment, case depth and hardness can be successfully detected by MAC’s comparators. The Varimac® eddy current comparator can be used on a range of product types including non magnetic stainless. Variations in carbon steel and special alloy bar can also be detected with the Production Comparator low frequency electromagnetic comparator.
In Situ Defect Detection in Heat Exchanger Tube
To detect defects such as corrosive pitting, holes, erosion, fatigue cracks, and OD wear at the tube supports in non magnetic heat exchanger tubing, an eddy current tester such as the Promac Mac 141 tester is appropriate. With optional tube mapping software, immediate tube maps can be printed to show test results. MAC also has test equipment which is suitable, with magnet test probes, for in situ detection in certain thin wall, small diameter magnetic alloys.
For applications where more than one of the conditions described above must be met, Multiple Test Systems using several testers or technologies can be assembled. In these cases, each tester or technology is used to find the types of defects or conditions that it is best suited to detect. The result is often a more accurate test and fewer rejects to allow more of your product to be shipped to your customer.