Weld Testing

33. Which nondestructive test is most commonly used?

Visual Inspection

22. What would be the elongation for a specimen for which the original gauge length was 2 in. and final gauge length was 2.5 in.?

• (2.5-2/2).*100=25

What would be the transverse shear strength per inch of weld if a specimen that was 2.5" wide withstood 25,000 lb?

• 25000/(2*2.5)=5000

5. What is a defect?

• A defect is a "discontinuity or discontinuities that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability."

What causes crater cracks?

• Crater cracks are the tiny cracks that develop in the weld craters as the weld pool shrinks and solidifies. • Materials with a low melting temperature are rejected toward the crater center while freezing. Since these materials are the last to freeze, they are pulled apart or separated, as a result of the weld metal's shrinking as it cools. The high shrinkage stresses aggravate crack formation. Crater cracks can be minimized by not interrupting the arc quickly at the end of a weld. This allows the arc to lengthen, the current to drop gradually, and the crater to fill and cool more slowly.

Why are all welds not inspected to the same standard?

• Different applications merit different degrees of inspection. For example a main nuclear reactor containment vessel vs. a fence post.

4. What is a discontinuity?

• Discontinuities and flaws are interruptions in the typical structure of a weld. They may be a lack of uniformity in the mechanical, metallurgical, or physical characteristics of the material or weld. All welds have discontinuities and flaws, but they are not necessarily defects.

37. How is the size of a flaw determined using ultrasonic inspection?

• Flaw size is determined by plotting the length, height, width, and shape using trigonometric rules.

How are the specimens bent for a guided-, root, face-, and side-bend test?

• Guided Bend test - one face bend and one root bend.

What information does a hardness test reveal?

• Hardness is the resistance of metal to penetration and is an index of the wear resistance and strength of the metal. Hardness tests can be used to determine the relative hardness of the weld with the base metal. The two types of hardness testing machines in common use are the Rockwell and the Brinell testers.

11. What are inclusions and how are they caused.

• Inclusions are nonmetallic materials, such as slag and oxides, that are trapped in the weld metal, between weld beads, or between the weld and the base metal. Inclusions sometimes are jagged and irregularly shaped. Also they form in a continuous line concentrating stresses and reducing structural integrity. They form when prior welds were improperly cleaned or had a pour contour.

What is the major limitation of eddy current inspection?

• It is only effective at searching for defects on or near the surface.

20. How can stress be reduced through a plate's thickness to reduce lamellar tearing?

• Lamellar tears appear as cracks parallel to and under the steel surface. They result from the thin layers of nonmetallic inclusions that lie beneath the plate surface and have very poor ductility. • A solution to the problem is to redesign the joints in order to impose the lowest possible strain throughout the plate thickness. This can be accomplished by making smaller welds so that each subsequent weld pass heat treats the previous pass to reduce the total stress in the finished weld. The joint design can be changed to reduce the stress on the through thickness section of the plate.

15. What is overlap?

• Overlap, also called cold lap, occurs in fusion welds when weld deposits are larger than the joint is conditioned to accept. The weld metal then flows over the surface of the base metal without fusing to it, along the toe of the weld bead.

34. List the five steps to be followed when using a penetrant test.

• Penetrant inspection is used to locate minute surface cracks and porosity. 1. Precleaning 2. Test surface must be covered with a thin film of penetrant by dipping, immersing, spraying, or brushing. 3. The test surface is then gently wiped, washed, or rinsed free of excess penetrant. It is dried with cloths or hot air. 4. A developing powder applied to the test surface acts as a blotter to speed the tendency of the penetrant to seep out of any flaws open to the test surface. 5. Depending upon the type of penetrant applied, visual inspection is made under ordinary white light or near ultraviolet black light when viewed under this light. The penetrant fluoresces to a yellow green color, which clearly defines the defect.

. How can porosity form in a weld and not be seen by the welder?

• Porosity results when gas that was dissolved in the molten weld pool forms bubbles that are trapped as the metal cools to become solid. The bubbles that make up porosity form within the weld metal; for that reason, they cannot be seen as they form.

What part of a fillet weld break test is examined?

• The break surface should be examined for soundness, that is slag inclusions, overlap, porosity, lack of fusion, or other discontinuities.

What information about the weld does an impact test provide?

• The impact resistance of the metal. This test compares the toughness of the weld metal with the base metal.

How are the results of a fatigue test reported?

• The results obtained are usually reported as the number of stress cycles that the part will resist without failure and the total stress used.

"What would a weld crack look like on an X-ray?"

• Transverse Crack - A fracture in the weld metal running across the weld. Feathery, twisting line of darker density running across the width of the weld image. • Longitudinal Crack - A fracture in the weld metal at the edge of the root pass. Feathery, twisting lines of darker density along the edges of the image of the root pass. The "twisting" feature helps to distinguish the root crack from incomplete root penetration.