Chapter 30 Inspecting and Testing Welds Objectives Differentiate

Chapter 30 Inspecting and Testing Welds

Objectives • Differentiate between destructive testing and nondestructive examination methods. • Describe various nondestructive examination methods and what flaws or defects they identify. • Identify and specify various nondestructive examination methods using the correct AWS abbreviation. • Make a visual inspection of a weld. • Perform a properly conducted dye penetrant test on a weld. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Objectives • Make a safe and proper bend test on a groove-type weld. • Describe and identify various laboratory and shoptype equipment used to make destructive tests on welds. • Visually inspect and perform a peel test on a spot weld. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Inspecting and Testing Welds • All welds have flaws • Discontinuities are interruptions in the normal crystalline lattice structure of a metal • Discontinuities are defects only when the weld is unsuitable for use • The welder should locate discontinuities • Nondestructive examination methods are used to do this without damaging the weld © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Inspecting and Testing Welds • Nondestructive testing is done to check a weld’s quality without damaging it • The role of destructive testing is to determine the effects of various discontinuities • The weld is destroyed in this type of testing process © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Nondestructive Examination • Fitness for service is the concept that all welds contain flaws • Flaws or discontinuities that are too numerous or too large are called defects • Tests are done to determine how large a discontinuity must be to become a defect • The maximum size limit is referred to as the critical defect size © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Visual Inspection • Visual inspection checks for size, contour, and location of the weld • A visual inspection can involve the use of templates and gauges • Visual inspection is limited to the external surfaces of the weld © Goodheart-Willcox Co. , Inc. (G. A. L. Gage Co. ) Permission granted to reproduce for educational use only.

Magnetic Particle Inspection • Magnetic particle inspection is most effective in checking a weld for surface or near-surface flaws • It is used only on materials that can be magnetized • The metal is subjected to a strong magnetic field • The magnetic particles in the applied powder or liquid are attracted to the cracks and pits by their magnetism © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Magnetic Particle Inspection • A kit containing the items necessary to perform a magnetic particle inspection is shown here • Another method used to create a magnetic field in a part is to pass high current through the part • Any flaw will attract the magnetic particles © Goodheart-Willcox Co. , Inc. (Magnaflux) Permission granted to reproduce for educational use only.

Magnetic Particle Inspection • A magnetic field can also be produced in the part by placing a permanent magnet on or near the part • A core or ring electromagnet is a third way to inspect a part using magnetic particle inspection (Magnaflux) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Liquid Penetrant Inspection • Liquid penetrant inspection uses colored liquid dyes and fluorescent liquid penetrants to check for surface flaws • The surface to be inspected should be completely cleaned • The excess penetrants must be removed • The developer is then applied • Some of the penetrant that is in a flaw will be drawn out © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Liquid Penetrant Inspection • The dye can be seen and the discontinuities located, as shown in this illustration • Fluorescent liquids are used in a manner similar to dye penetrants (Dennis Nance, CWI Consultants Co. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Ultrasonic Testing • Ultrasonic testing is a nondestructive method of locating flaws by means of sound waves passed through the material • It can be used on virtually any type of nonporous material • An electronic device called a transducer is placed on the material • To ensure good contact, a material called a couplant is used © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Ultrasonic Testing • Ultrasonic waves are sent into the material for very short periods of time • The wave is reflected from surface boundaries or flaws where density changes occur • During the test, the transducer is moved along the material’s surface • Each reflected wave signal is amplified and shown on a display © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Ultrasonic Testing • This illustration shows a search pattern and a display calibrated to show distance (Panametrics, Inc. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Ultrasonic Testing • The equipment used is light and portable • The process is fast and gives immediate results on most materials • Defects parallel to the sound beam are difficult to detect • Operators must be trained to interpret the display correctly © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Eddy Current Inspection • Eddy current inspection uses an ac coil to induce eddy currents into the part being inspected • The coil is calibrated or adjusted to obtain a set value of impedance • The coil is moved over the surface of the part • If a discontinuity is present, it interrupts the flow of the eddy currents © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

X-Ray Inspection • Welds can be checked for internal flaws by means of x-ray inspection • X-ray energy is produced electronically in an x-ray machine • A radiograph (x-ray picture) is a permanent record of welds made on construction sites or critical components © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

X-Ray Inspection • When looking at a radiograph, the location of a flaw can be identified • The energies required to x-ray different materials and different thicknesses vary considerably © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Inspecting Welds Using Pneumatic or Hydrostatic Pressure • A common method of testing pressure-vessel welds for leaks is to use gas or air pressure • Carbon dioxide gas is well-suited for this purpose • Another test for pressure vessels is hydrostatic pressure testing • Hydrostatic pressure testing applies pressure to a closed pressure vessel or pipe © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Inspecting Welds Using Pneumatic or Hydrostatic Pressure • This test proves the item is fit for service • Water is used instead of gas for hydrostatic testing • If a failure occurred during a test made with gas, there could be a violent explosive failure • Water is not a reliable test for extremely small leaks © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Destructive Tests • Destructive tests are used to determine the physical properties of a weld • Destructive tests render the weld unfit for further service • A side bend test, shown in this illustration, is one type of destructive test © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Bend Tests • In a bend test, a sample of the weld and surrounding base metal is bent and checked for cracks • This testing method is fast and reveals most weld faults • Bend tests done with the weld going across the test sample are called transverse bends • If the face of the weld is on the outside of the bend, it is called a transverse face bend © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Bend Tests • If the root of the weld is on the outside, the bend is called a transverse root bend • If a very thick metal has been welded, a side bend is performed • Longitudinal face and root bends are done with the weld going along the length of the test sample • After bending, each bend sample is examined for defects © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Bend Tests • A poorly made weld has large cracks after bending • In an unguided bend test, a welded piece is clamped in a vise or jig just below the weld and the metal is bent to an angle of about 90° © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Safety • A screen or curtain should be used around the vise when doing an unguided bend test • This is to protect other workers from flying pieces if the weld should break © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Bend Tests • A fillet weld bend test requires that a fillet weld be made on one side of a T-joint • The vertical piece is then bent over the weld until the weld fails or until it is bent flat against the horizontal piece © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Tensile Test • In a tensile strength test, a prepared sample is pulled in a tensile testing machine until it breaks • Three values can be obtained from a tensile test – Tensile strength – Yield point – Ductility © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Tensile Test • The elastic limit of the metal is the stress it can withstand still return to its original length after the load is released • The yield point or yield strength occurs when the specimen stretches or gives at a certain loading, but it does not break • Ductility is a measure of how much a sample stretches or elongates before it breaks © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Nick Break Test • The nick break test is a field test • Coupons are cut from a pipe in locations indicated in the specification • The coupon is usually placed in a vice with the nick slightly above the vice jaws • A force is applied to break the coupon • After breaking the coupon, the fractured weld surface is inspected © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Peel Test • In a peel test, two joined pieces of metal are pulled apart until they separate • If the spot weld nugget is of the correct diameter and is torn out in one piece, the spot weld is properly made © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Laboratory Methods of Testing Welds • Most large companies that perform welding operations have laboratories for testing the welds • Tests performed are to study the following – – – Impact straight Hardness Microstructure Macrostructure Chemical analysis © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Impact Tests • The impact test may be made by either the Izod method or Charpy method • Test samples are taken from the weld, the heataffected zone, and the base metal • The indicator needle on the testing machine shows what force was exerted to break or fracture the test specimen © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Hardness Testing • Hardness can be defined as a resistance to permanent indentation • The most popular method for testing hardness is the Rockwell hardness test • There are different ranges or scales of Rockwell hardness testing • The Rockwell B test is used on materials like copper alloys, soft steels, and aluminum alloys © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Hardness Testing • The Rockwell C test is used on harder materials like steel, hard cast irons, and titanium • A similar testing method is to use a Brinell hardness testing machine • After the load is tested and removed, the diameter of the indentation is measured using a microscope © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Hardness Testing • Microhardness testers have been developed that make it possible to test the hardness on a very small area • This illustration shows a microhardness testing machine (Instron®) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Microscopic Method of Testing Welds • Usually, the sample being studied is treated with acid, or etched • To etch a sample after it has been polished, it is wiped with a weak acid solution • The sample is then placed under a microscope, which magnifies the surface of the metal (Leica Optical Products Division) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Microscopic Method of Testing Welds • The microscope reveals the grain size and microstructures of the metal • Impurities can be identified • Photographs can be taken of the metal by means of a camera attached to the microscope © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Macroscopic Method of Testing Welds • A microscopic view of a weld does not cover enough area to obtain a picture of an entire weld for inspection purposes • Macroscopic pictures are only 10 to 40 magnifications and are better suited to this purpose • Cracks, pits, and pin holes are clearly seen with this method © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chemical Analysis Method of Testing Welds • The complete investigation of welded material consists of a thorough chemical analysis – Qualitative analysis determines the different kinds of chemicals in the metal – Quantitative analysis determines the kind amount of each chemical in the metal • A chemical analysis is usually used when large quantities of metal are believed to be of the wrong composition © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Review of Safety • Proper inspecting and testing of welds requires attention to certain safety factors • There is a danger of parts flying when the weld is broken • You should avoid exposure to radiation from x-ray machines used to inspect metals • Only trained experts should work with x-ray equipment © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Safety • A face shield should be worn to protect the operator • The operator should never stand in the likely trajectory of a flying test piece • Proper signs should be used to warn people that xray inspection is being performed • Proper protection should be used by the operator to minimize any x-ray exposure © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.