manufacturing processes lab 1 (met 1321) dr simin nasseri manufacturing processes lab i, met 1321...

Manufacturing Processes Lab 1 (MET 1321)Dr Simin Nasseri

Manufacturing Processes Lab I, MET 1321Inspection and Testing Welds

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Learning Objectives

Describe the difference between a welding flaw and a welding defect.

List the most common types of nondestructive and destructive testing done on welds.

Perform several basic types of tests on welds to evaluate weld quality.

Describe the methods used to prepare samples for bend tests.



Reasons for inspecting weldsMost welds have flaws in themA flaw is a part of a weld that is not perfect.Some flaws are so small they can be found only under a

microscope.Other ones are easily seen, which include porosity and large

cracks.

A defect is a flaw that makes a a weld unusable for the job it is intended to perform (eg. Cracks when welding on a gas pipeline)



Inspecting welds

Welds must be inspected to detect flaws. Then, the flaws must be evaluated to decide if they are acceptable or if they are defects.

Most welding is done to requirements of a code or specification. The code or specification determines how large a flaw can be before it becomes a defect.

A visual inspection is useful to determine the size of a weld, to check for undercut, overlap, and other surface flaws, and to check travel speed, arc length, and depth of penetration.



Weld tests

Weld tests

Nondestructive Destructive

NON-destructive Examinations (NDE), does not damage the

weld or the base metal.

Destructive test results in at least

some damage to the weld.



Nondestructive Examinations (NDE)



Nondestructive Examinations (NDE)

Liquid penetrant inspections,Magnetic particle inspections,Ultrasonic inspections,X-ray inspections,Eddy current inspections andAir pressure/water pressure leak tests.



Liquid penetrant inspections

In a liquid penetrant inspection, a dye is applied to the weld. After a few minutes, the dye is cleaned from the weld and a developer is applied. Any dye trapped in a flaw is developed, revealing the location of the flaw.

Liquid penetrant inspections are useful for detecting surface flaws, but cannot detect

flaws inside the weld!



Magnetic particle inspectionsTo examine a part using magnetic particle inspection, the

surface must first be cleaned. Then, fine magnetic particles are applied to the surface. Then a strong magnetic field is applied. The fine magnetic particles are drawn toward any flaw at the surface or very near the surface of the part.



Ultrasonic inspections

Ultrasonic inspection can be used on all metals and can locate internal flaws.

Sound waves are sent into the part being inspected.

The waves travel to the far side of the metal and bounce back.

Any flaws within the weld are indicated on an oscilloscope.



X-ray inspectionsIn an X-ray inspection, film is placed on one side of the part to

be inspected. X rays pass through the part and expose the film. After the film is developed, any flaw or defect in the weld can

be observed.



Eddy current inspectionsEddy current inspection detects porosity, cracks, slag inclusions, and lack of fusion at or near the surface of a weld by including eddy currents in the part and monitoring changes in current flow on an oscilloscope.

Eddy currents are AC currents, usually of high frequency, which can be induced to flow in any metallic section, their flow pattern being disturbed by the presence of cracks or other discontinuities.



Air pressure leak testsAir-pressure or water pressure leak tests are often used to inspect pipes or tanks that are to contain gases or liquids under pressure. In an air-pressure leak test, a soapy solution is applied to

the pipe surface at each weld. When the pipe is under air pressure, flaw will cause bubbles to form.

When water pressure is used, water will spray out from the pipe where there is a leak.



Destructive Examinations (DE)

Tensile test,Bend test,Fillet test,Hardness test,Impact test,Peel test (for spot welds),Tensile shear test (for spot welds),Pressure test.



Tensile testA tensile test is a destructive test in which a tensile

(stretching or pulling) load is applied to a prepared sample until the sample breaks.



Tensile Strength and Ductility

Tensile strength=Maximum force applied by machine

Cross-sectional area of sample

F

o



Ductility

Ductility= x 100

Distance between points after test – distance before test

distance before test



ExampleA 2 inch welded plate is ½” (12.7 m) thick. The reduced section is 1 ½” (38 mm) wide. A maximum force of 48000 pounds (213500 Newtons) is required to break the sample. The distance between the two points after breaking is 2 ½” (63.5 mm). Find the tensile strength and ductility of this sample.

Tensile strength= = = 64000 psiMaximum force applied by machine 48000

Cross-sectional area of sample ½ x 1 ½

= 442 MPa

Ductility= x 100= x 100= 25%

Distance between points after test – distance before test

distance before test

(2 ½” -2”)

2”The same value in metric system.



Bend testSpecimen is positioned between two supports, and a load is

applied at its center.Bend tests are used to evaluate the quality and ductility of a

completed weld.



Bend testIn a guided bend test, the size or radius of the bend is

controlled.

Click on image to see the video clip



Bend testIn a free bend test, the sample is placed into a large, strong vise

and struck with a hammer until it bends to a 90˚ angle. It is then hammered in the opposite direction to a 90˚ angle. This back and forth bending continues until the weld sample breaks.



Fillet testIn a fillet test, force is applied to the welded joint until it breaks or until the vertical piece is bent flat against the horizontal piece.

The weld should break along its centerline.

A weld that breaks along the toe may indicate a lack of fusion.



Hardness testHardness tests are used to measure a material’s resistance to scratching and indentation.

To determine the hardness of a metal, an indenter is pressed into the metal by a known force. The depth of indentation indicates the hardness of the metal.



Other destructive tests

Impact resistance test



Other destructive tests

Peel test (for spot welds)

Tensile shear test (for spot welds)



Check this site!

http://64.78.42.182/sweethaven/BldgConst/Welding/lessonmain.asp?lesNum=7&modNum=13


manufacturing processes lab 1 (met 1321) dr simin nasseri manufacturing processes lab i, met 1321...

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