3Al-2.5V Titanium Seamless Tube – Inspection & Testing

For critical tubing applications such as aerospace, not only must the tubing be of a very high quality, but the testing and inspection methods must provide positive assurance that all specification requirements have been met. Test and inspection methods must be in accordance with industry standards, and the measurement must be precise and accurate. To assure the quality of the tubing, specifications and test methods must be clearly defined in the quality assurance plan and records must be traceable to each tube lot. These records are retained for many years to provide traceability in event that problems may arise during service life of the tubing.

FD Titanium has more than 10 years of experience in 3Al-2.5V Seamless Tubes. meet the Specifications AMS4943, AMS4945. If you have any questions or requirements, please contact us by email or leave a message below.

Inspection for 3Al-2.5V Tube

Every tube in each lot is inspected to ensure conformance to dimensional tolerances, surface finish requirements and freedom from obvious visual flaws. Nearly all specifications now require that the full length of each tube be subjected to all aspects of the inspection process. Only in rare cases is inspection by a sampling plan employed for products of hydraulic tube quality.

Visual inspection for 3Al-2.5V Tube

Visual inspection of the tubing is the first step of the inspection process. It is also performed again just prior to packaging as a final check for proper marking, cleanliness and any handling damage that may have occurred after the initial inspection.

The inspection methods for tubing dimensions may be accomplished by several methods including: hand micrometer, air gauges, laser micrometer or ultrasonic testing (UT). The choice of test method depends upon the importance of dimensions to the application of the tubing. For aerospace hydraulic tubing, where dimensional control is important for performance of the tubing as well as for bending and attachment of fittings, the best method is three dimensional ultrasonic inspection.

Ultrasonic dimensional inspection for 3Al-2.5V Tube

The use of ultrasonic dimensional inspection allows one to scan the entire length of the tube in a tight spiral pattern. This assures that dimensional tolerances, (diameters and wall thickness), are met over the whole tube. Measurement by micrometer is less expensive than dimensional UT but only allows for spot checking OD and can only measure wall thickness at the ends of the tube.

Ultrasonic testing of dimensions involves passing the tube within a water bath, in a spiral path between two opposed transducers. The tubing outer diameter can be determined using the precise timing of the reflections from the outer surfaces of the tube. The same sound beams also penetrate the tube wall and measures the wall thickness; again by precise timing of the interval between the reflections from the two sides of the tube wall. A small microprocessor in the inspection equipment subtracts the two measurements of wall thickness on opposite sides of the tube from the OD measurement to obtain the inner diameter. The signals for the OD, ID and wall thickness can be displayed on a CRT screen and recorded on chart paper or magnetic disk. At FD Titanium, the equipment also automatically sprays any portion of the tube which deviates from set limits with colored ink denoting the type of deviation.

Flaw detection is accomplished by ultrasonic search unit since the largest permissible OD surface flaw is far too small to be seen visually and the inner surface must also be scanned. Permissible flaws must be smaller than 0.002 in (0.05 mm) in depth and less than 0.060 in (1.5 mm) in length. The search for flaws is done in the same manner as the ultrasonic dimensional inspection and can be done concurrently. However, the search for flaws utilizes four transducers: two looking longitudinally, one in each direction along the tube, and two looking circumferentially around the tube, again in each direction.

Ultrasonic equipment is calibrated against a “standard,” that is a section of tubing with notches of a specified size produced by electric discharge machining. These notches in the standard produce a sound reflection that is measured by the equipment. The amplitude of these standard reflections form the basis for acceptance or rejection of the tubing. In the case of the flaw search, the spiral path is arranged so that 100 percent of the tube surface and volume is scanned by sound waves in all four directions. The amount of sound reflected from a flaw in the tube is compared to the reflection from the notch in the standard and any indication greater than the established level is marked by the ink spray for removal during the cut-to-length step. Tubing can be ultrasonically inspected for both dimensions and flaws at rates up to 350 feet (100 M) per hour, depending on tube size. Tubing with small surface flaws or deviations from dimensional limits can sometimes be reworked to correct the condition and then completely reinspected prior to acceptance.

Lot Testing for 3Al-2.5V Tube

Samples for destructive testing are taken from the lot as required by the specification. A wide variety of test methods are used to determine conformance to requirements. Sampling frequency varies with the test and lot size but generally two or three samples from each lot are tested to determine compliance.

Chemistry for 3Al-2.5V Tube

Lot testing for chemistry is generally limited to the interstitial gases: oxygen, nitrogen and hydrogen. The other alloying elements and impurities are determined on samples taken from the ingot from which the tubing was produced.

Tensile Testing for 3Al-2.5V Tube

Longitudinal tensile tests performed at room temperature are the most common mechanical tests employed. Ultimate tensile strength, 0.2 percent offset yield strength and elongation at fracture are determined in this test. Strict adherence to strain rate requirements is essential to obtaining correct values in this test. The yield strength rises markedly with increasing rate of strain. The observed elongation in a tensile test decreases as the diameter of the tube being tested decreases if the gage length, usually 2 inches (50 mm) is not decreased as well. Most specifications do not recognize the effect of this slenderness ratio and specify the same elongation value for all tube diameters. Other specifications, such as AMS 5561, do specify different values for different diameters. Another approach is to leave the elongation value constant but vary the gage length used to determine it. When this is done, the value of the gage length is usually four times the tube diameter. The slenderness ratio is recognized in ASTM E-8 where the gage length to specimen diameter is maintained at four. Large diameter tubing can be tested using a tensile specimen cut from the wall of the tubing as specified in ASTM E-8 . Specimens of this type give an accurate measure of ultimate and yield strength but show much lower values for elongation than the same tube will exhibit if the full cross section is tested.

Bend Test for 3Al-2.5V Tube

A bend test requiring that the tubing be bent 180 degrees around a die to produce a U shape with a centerline radius three times the tube diameter is the usual requirement. No cracks or excessive ovalization of the tube in the bent region is permitted. This test requires very specialized tooling for each tube size to be bent. Dies to form the bend, and mandrels to support the inside of the tube during bending, are required for each size tube to be tested. Excessive clearance between the tube and mandrel will produce poor bends. In some cases, special ball or ring-type mandrels are needed to make the required bends. Lubrication is also important as is the technique and tooling. The test is done on equipment of the same type as is used in the production bending of hydraulic tubes.

Flare Test for 3Al-2.5V Tube

A flare test is often specified where a cone shaped end is formed on the end of the sample of tubing. The usual requirement is that a certain diameter expansion be accomplished with a given cone angle without evidence of any cracking when the sample is viewed at 5X magnification. The flare configurations developed for steel or aluminum were referenced in early titanium specifications. However, the configurations taken by titanium when flared over a cone were actually quite different from those of steel or aluminum because of the strong anisotropy of titanium alloy tubing. The radius at the root of the flare cone must be larger to accommodate the anisotropic behavior of titanium. Flare testing is one of the requirements where the wall thickness must be considered when setting the requirements. Flaring can be accomplished by a variety of techniques and equipment each making a different evaluation of ductility by virtue of the way the metal is deformed in producing the flare. Since flare type fittings are no longer in wide use, the test is of limited interest though still a part of many specifications.

Flattening Test for 3Al-2.5V Tube

A flattening test is also used as an index of ductility. Here, either a complete cross section of the tube or a half section is flattened between parallel plates until a specified dimension between the plates is reached. Again in this case, the criteria for acceptance is the absence of cracks when viewed at 5 to 20X magnification. This test, like the flare test, presents problems in performance and interpretation. The tube does not always remain in contact with the parallel plates as it is being flattened but tends to form a reverse bend in the center of the section as shown in Figure 7-5. Cracks form in this region and it is common practice to end the flattening when the reverse bending begins to occur. Tubes with relatively thick walls are particularly prone to the reverse bending phenomenon. Lubrication and the preparation of the specimen edges of split samples also strongly affect the results of this test as they change the strain patterns in the tube sample.

Pressure Testing for 3Al-2.5V Tube

Pressure proof testing is another common requirement for hydraulic tubing. In this test a sample of the tubing is pressurized internally to produce a stress in the tubing well beyond that to be encountered in service. After pressurization, the sample is examined for bulges or other localized evidence of yielding. Bursting during the test quite obviously constitutes failure. A variation of this test where the tube is pressurized to failure and the failure pressure or the calculated failure stress is recorded, is less frequently employed. Again, when thick walled specimens are encountered the pressures may have to be limited to about 20,000 psi (138 MPa), because simple end fittings will not carry higher pressures.

Cleanliness Test for 3Al-2.5V Tube

Cleanliness tests requiring that a sample of the finished tubing be split in half longitudinally and then one-half etched in acid for comparison to the as-manufactured half is a common test for surface contamination. This test recalls earlier times when vacuum furnaces were not as reliable in maintaining freedom from oxidation during heat treatment as present vacuum furnaces.

Contractile Strain Ratio (CSR) for 3Al-2.5V Tube

The profound influence of crystallographic texture on the properties of tubing makes this property very important as was discussed in Section 5. The CSR determination is a relatively new test now being used to specify texture in product specifications. The contractile strain ratio, or CSR, is determined by careful measurements made on a tensile test specimen. The specimen is coated with layout ink and circumferential lines scribed in the ink at one inch intervals. Longitudinal lines are scribed at 90 degree increments to orient diameter measurements. The distance between the circumferential rings is carefully measured to the nearest 0.0005 inch (0.01 mm). The diameters are measured to the nearest 0.0001 inch (0.0025 mm). The specimen is then strained in a tensile machine to 4 percent elongation. After removing the specimen from the testing machine the measurements are then repeated. Accuracy in scribing the lines and making the measurements is essential if reproducible results are to be obtained. Figure 7-6 illustrates a device for scribing and measuring the specimen. A laser micrometer is a very convenient and accurate way to determine the precise average diameter of the specimen. Diameter measurements must be made to the nearest 0.0001 inch (0.0025 mm) as this measurement has the greatest effect on the compound CSR value. Measurements with an ordinary hand micrometer are not precise enough for this test. The contractile strain ratio is the plastic strain in the circumferential direction divided by the plastic strain in the thickness direction. Circumferential strain is measured directly as the change in diameter but the change in wall thickness is too small and difficult to measure accurately and so is calculated from the longitudinal and circumferential strains and the assumption that the test specimen volume remains constant. The CSR test method is specified in AS 4076.

Metallurgical Tests for 3Al-2.5V Tube

Microstructure of the tube material is sometimes specified either as a grain size in accordance with ASTM E-112 or simply as a test for identifying large alpha stabilized grains, indicating contamination with oxygen. Cold-worked, stress-relieved titanium alloy tubing has a complex flow-like microstructure that does not lend itself to evaluation against the ASTM grain size charts or the alternate methods widely used for other materials. The tubing structure is elongated from the cold working and complicates interpretation. If structure is an important property, a set of comparative standard structures should be established to ensure that the desired features are obtained.

Choice of Tests for 3Al-2.5V Tube

Choosing the tests to correctly reflect the service requirements of the application is a complex task as many combinations can be specified. Obviously as the specified strength is increased, the ductility will be reduced. Ductility, as measured by the tension test, the flare test, and the flattening test, are all quite different. Each represents ductility in a different direction. Titanium is an anisotropic material and tube manufacture heightens this feature. Mechanical properties are quite different in the longitudinal direction from those found in the circumferential direction. Test requirements must be tailored to the end-use application to obtain tubing that will perform the best. Too often, this has been a neglected part of procurement engineering, where a single specification is used for many quite different applications. A wide variety of properties can be provided in titanium tubing when the needs of the application are made known to the tube manufacturer.