Weld assessments and weld properties

Weld assessments and weld properties Subjects of Interest

Part I Weld assessment • Destructive testing • Non destructive testing

Part II Weld properties • Mechanical properties • Corrosion in weldment

Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Objectives This chapter aims to:

• This chapter provides information on weld mechanical assessments: Destructive testing and non destructive testing (NDT). • Students are required to analyse mechanical properties and corrosion of weldments, such that information can be used for the selection of the weldments in service.


Tapany Udomphol

Sep-Dec 2007

Weld assessments • Weldments normally contain defects. However we need to keep weld defects at a minimum level to maintain reliable products. Swing arm

Longitudinal crack

Pressure vessel weld joint heat treatment


Crater cracking

Tapany Udomphol

Sep-Dec 2007

Weld assessments Appropriate welding method

Reliable products

Specifications Quality control method

• Destructive testing

• Non destructive testing

• Mechanical testing, i.e., tensile, fracture toughness, impact, fatigue tests.

• Weldments are not destroyed. • Many NDT techniques are expensive and have their own limitations. • Inspection should be carefully planned to make sure the technique used is capable of detecting the concerned defects.

• Expensive, require specimen preparation under standard specifications.


Tapany Udomphol

Sep-Dec 2007

Destructive testing • Mechanical tests are destructive testing, which are expensive since it requires specimen preparation and then destroying it. • The orientation of the weld in the testpiece must be recorded. • Requires standard specimen dimension for each specification used.


Tapany Udomphol

Sep-Dec 2007

Destructive testing • Mechanical tests are destructive testing, which are expensive since it requires specimen preparation and destroying it. • The orientation of the weld in the testpiece must be recorded. • Requires standard specimen dimensions for each specification used.

Method of cutting test-pieces from procedure approval plate. Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Destructive testing

Tensile test specimen

AWS all-weld metal test


Tapany Udomphol

Sep-Dec 2007

Destructive testing

Three types of bend test Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Destructive testing

AWS fillet break test.


Tapany Udomphol

Sep-Dec 2007

Destructive testing

Impact Charpy V notch specimens Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Destructive testing

PN

P

PQ

N

NQ

Q

NP

N = Normal to the weld direction P = Parallel to the weld direction Q = Weld thickness direction First letter : the direction normal to the crack plane Second letter: the expected direction of crack propagation Specimen orientations NP and PN are referred to as through-thickness notched Specimen orientations NQ and PQ are referred to as surface notched (c) EB and TIG welds


Tapany Udomphol

Sep-Dec 2007

Non-destructive testing • We must remember that NDT result itself cannot guarantee whether the weld is acceptable, but can only report what types of defects we discover. There are a range of NDT techniques available;

• Visual inspection • Liquid penetrant inspection • Magnetic-particle inspection • Radiography • Ultrasonic inspection Note: At least one of the NDT methods should be taken for weld inspections. Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Visual inspection • Weld defects can often be discovered by naked eyes and can be repaired at this stage:

• Weld dimensions • Joint penetration • Surface defects

Simple fillet-weld gauges Suranaree University of Technology

Check on defects • Surface cracks • Crater cracks • Incomplete root penetration • Undercut • Underfill on face, groove, or fillet (concave) • Underfill of root (suck back) • Excessive face reinforcement, groove, or fillet (convex) • Excessive root reinforcement • Overlap • Misalignment • Arc strikes • Excessive spatter • Warpage (distortion) • Base metal defects Tapany Udomphol

Sep-Dec 2007

Weld size measurements • It is important to measure weld size. • Size of fillet welds can be easily measured by using weld gauges (different standard gauges used:

Fillet weld size and method of checking Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Liquid-penetrant inspection • Used to detect minute discontinuities such as cracks, pores, which are open to the surface. • Can be applied to ferrous & non ferrous metals, glass and plastics. • The surface must be clean.

Properties

• Low surface tension • Low viscosity • Can be dye or fluorescence

Liquid panetrant

• Liquid penetrant inspection is portable and very easy to use on site. • Required appropriate protections because the liquid used might be toxic. • Limited on surface inspection and should be used in combination of other NDT techniques. Principle of penetrant examination Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Method and applications • The liquid penetrant (normally red) is applied on the surface containing cracks. • Waiting for the liquid penetrates into the cracks. • Clean off the excess liquid from the surface, but some liquid still remains in the cracks. • Developer (chalk emulsion) is applied to enhance the visible indication of cracks.

Principle of liquid-penetrate inspection

Note: Ultraviolet or black light source are used for the inspection of fluorescence liquid penetrant. Sound areas appear deep violet while the defects will glow a brilliant yellowish green. Suranaree University of Technology

Tapany Udomphol

www.instytutgamma.com

Liquid penetrant indication

Sep-Dec 2007

Method and applications • Used to detect defects in aluminium, magnesium, and stainless steel weldments, when magnetic particle inspection cannot be used. • Locating the cracks, leaks in all types of welds, weld in pressure, storage vessels, piping for petroleum industry.

www.bbrail.com


Tapany Udomphol

Sep-Dec 2007

Magnetic particle inspection • Magnetic particle inspection is used to detect cracks porosity, seams, inclusions lack of fusion and other discontinuities in ferromagnetic materials. • Used on the surface and shallow subsurface. • The lines of force within the magnet run smoothly from S to N. • When a crack is present, N and S poles are set up at the edges of the crack. • The magnetic particles will be attracted to the crack (poles).

Magnetic fields around bar magnet and a crack


Accumulation of magnetic particles on defects

Tapany Udomphol

Sep-Dec 2007

Method and applications • Establishing a magnetic field in the test object. • Applying magnetic particles to the surface of the test object. • Examining the surface by detecting accumulation of magnetic particles where the defects are.

Cracks

Accumulation of magnetic powder indicating the location of the cracks or defects.

• Iron particles can be applied dry or wet.

Applying magnetic particles Suranaree University of Technology

• Detecting fluid is normally particles of magnetic iron oxide suspended in kerosene and may be coated with fluorescence compound for viewing under ultraviolet light. Tapany Udomphol

Sep-Dec 2007

Method and applications • Magnetic particle inspection can be applied to any kinds of welds. • Can be used to detect defects on each pass in multi-pass welding after it has been deposited. • Parts may have to demagnetized after inspection.

Magnetic particle inspection using alternating current


Tapany Udomphol

Sep-Dec 2007

Radiographic examination • Interior defects (porosity, cracks, voids) can be examined by using X-ray or gamma ray, which can penetrate through materials and its intensity depends on materials thickness and density. • Provide a permanent film record which is easy to interpret. • Slow and expensive, however this method is positive to determine defect size. • X-ray is generated by electron bombardment on tungsten. • Gamma ray is emitted by radioactive elements. • X-ray or gamma ray is absorbed during transmission through the materials. • Pores or defects absorb less energy than uniform areas giving a variation of intensity of the beam generated on the film placed underneath the materials. Suranaree University of Technology

Principal of radiography Tapany Udomphol

Sep-Dec 2007

Method and applications • Exposure time: X-ray 10 s to 10 mins, gamma ray 1 min to 24 hours • After exposure, the cassette is developed and fixed in the dark room. • The film is then view against the bright light.

Radiogram

Setting up to take radiograph Examination of radiograph


Tapany Udomphol

Sep-Dec 2007

Method and applications • Different intensity of the beam due to discontinuities or defects in the weld shown on the film. Sound area

Light

Defect

Dark

Typical radiograph

• Radiography detection also depends on orientation of the flaw with respect to the beam. • Used to detect defects in all types of weldments and materials such as aluminium, steel, magnesium. • Used in pipeline industry. Orientation of flaw with respect to X-rays Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Precautions www.arrowheadproducts.net

• Require concrete, steel, leadlined bricks to house the X-ray to protect the operator from exposure. • On site operation is carried out in distance. • X-ray is more manageable than gamma ray. The area is safe when switching off the X-ray source while a radioactive isotope emits radiation continuously and must be kept in a shield container.


Tapany Udomphol

Sep-Dec 2007

Ultrasonic inspection • A beam of ultrasonic vibration produced by quartz crystal is directed into the specimen to detect defects or discontinuities. • Sound area gives small loss of signal, except when the ultrasonic is intercepted and reflected by defects. www.instytutgamma.com

Ultrasonic inspection of aluminium Ultrasonic inspection Suranaree University of Technology

Tapany Udomphol

Sep-Dec 2007

Ultrasonic inspection There are two ways of using ultrasonic waves for welded joint inspection.

Reflection

Transmission


Tapany Udomphol

Sep-Dec 2007

Method and applications • The location of the defect in the weld can be calculated. • Can be used to test all kinds of metals and materials, complex weldments. widely used.

www.olympusndt.com

Moving the probe to scan the thickness of the weld with an angle probe.


Ultrasonic inspection in pipeline

Tapany Udomphol

Sep-Dec 2007

Guide to weld quality control techniques


Tapany Udomphol

Sep-Dec 2007

Weld properties • Weldments normally possess a degradation of weld properties due to changes in microstructures and defects. • Weld properties should be assessed in order to correctly select the weldment, which can satisfy the condition in service.

• Tensile properties • Hardness • Toughness • Fatigue • Corrosion


Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Hardness profile

Hardness test orientation in the weld joint of AISI 1040 friction weld


Hardness profile

Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Tensile properties


Crack initiated at the weld zone Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Impact properties

Fractography of weldments tested at (a) Room temperature (b) 700oC Fractography of base metal at (a) Room temperature (b) 700oC


Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Impact properties Charpy Impact Energy vTemperature 160

140

Im p act En erg y (J)

120

100

As Deposited

80

Reheated

60

40

20

0 -200

-150

-100

-50

0

50

100

Temperature (oC)


Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Fatigue properties

1000 R = Pmin/Pmax = 0.1 Frequency ~ 70 Hz

• Lower fatigue limit was observed in autogenous TIG weld of titanium alloys in comparison to the base metal.

σmax, MPa

800

600

400

200 1e+3

1e+4

1e+5

1e+6

1e+7

1e+8

Number of cycle TIMET bar III, AR Autogenous BuRTi TIG weld, HT Ti679-BuRTi-Ti679 TIG weld, AR


Tapany Udomphol

Sep-Dec 2007

Mechanical properties of weldments Fatigue properties 1e-1

• Factors affecting the FCG results are coarsening microstructure, embrittlement, precipitation hardening, etc.

1e-2

da/dN, mm/cycle

• Fatigue crack growth is faster in the weld joint than in the base metal.

R = Pmin/Pmax = 0.1 Frequency = 0.25 Hz TIMET bar III m = 2.02 BuRTi EBW01 m = 9.05 BuRTi EBW02 m = 2.35 Ti679-BuRTi-TI679 TIG01 m = 6.84 Ti679-BuRTi-Ti679 TIG02 m = 10.18

1e-3

1e-4

1e-5

1e-6 1

10

100

∆K, MPa.m1/2


Tapany Udomphol

Sep-Dec 2007

Corrosion of weldments www.forensicmetallurgy.com

PLUMBING - PIPING

Corrosion in weld joint

•Corrosion failure of underground propane pipe •Broken stainless steel air injection pipes in a sewage treatment plant •Cracking of brass inserts in fire sprinkler head adaptors •Freeze failure of copper plumbing and air conditioner fittings •Dry solder joints in copper plumbing fittings •Pitting corrosion of copper pipes using well water •Pitting of air conditioner copper heat exchanger chillier water tubing •Corrosion of steam boilers •Rust clogging of high rise building steam heating systems •Leakage of propane from a connector fitting with a worn rubber seal •Corrosion failures of underground fuel tanks


Tapany Udomphol

Sep-Dec 2007

References • Gourd, L.M., Principles of welding technology, 3rd edition, 1995, Edward Arnold, ISBN 0 340 61399 8. • Cary, H.B., Modern welding technology, 4th edition, 1998, Prentice Hall, ISBN 0-13-241803-7. • Sahin, M., Akata, H.E., Gulmez, T., Characterization of mechanical properties in AISI 1040 parts welded by friction welding. 2006. • K.S. Guana, X.D. Xub, Y.Y. Zhangb and Z.W. Wang, Cracks and precipitate phases in 321 stainless steel weld of flue gas pipe, 2005, Vol.12, Issue 4, p 623-633.


Tapany Udomphol

Sep-Dec 2007