Metallurgical defects-gas porosity, Mechanical Engineering

Assignment Help:

Gas Porosity


Porosity is the presence of gas pockets or voids caused by the entrapment of gas evolved during weld metal solidification. This Porosity is caused due to improper shielding, rust on the weld face, too much generation of gas in weld pool, fast cooling of slag, etc. Sometimes elongated tubular gas pockets are called worm holes. It is seen by testing that porosities reducing the cross sectional areas of the weld upto 5 % have no significant effect on the strength, ductility or toughness. But, when porosities are present near the surface, it could lead to failure on bend test. Porosity is considered to be the least dangerous defect but is often an indication of damp electrodes having been used.

Pores in welds in mild steel are therefore normally regarded as harmless as regards the reliability of a welded joint provided that the weld is not working under corrosive conditions and when the thinner weld material at the pores can cause leaks after a short time.

Porosity in weld in high tensile steels is a warning of hydrogen cracks in the weld metal and the heat affected zone. Pores are often linked together by a hydrogen crack.

In static test, porosity will affect fillet welds much more adversely than butt welds. The different types of porosity are

  1. Random porosity (Less Severe)
  2. Linear or aligned porosity (more severe)
  3. Cluster porosity (Moderate / More severe)
  4. Blow holes (size is greater than 1/6" )
  5. Worm holes / spring
  6. Micro porosity - Seen under microscopes only
  7. Starting porosity - formed during starting of welding
  8. Scattered porosity
  9. Pin holes


Porosity is easily detected by radiography. Surface pores are usually detected by LPI.


Related Discussions:- Metallurgical defects-gas porosity

How can you determine velocity by electromagnetic method, Q. How can you de...

Q. How can you determine velocity by electromagnetic method? In electromagnetic method, a magnetic field is generated by the electric current flowing through a coil fixed below

Define gas welding, Q. Define Gas Welding? Metal joining process in whi...

Q. Define Gas Welding? Metal joining process in which the ends of pieces to be joined are heated at their interface by producing coalescence with one or more gas flames (such a

Key words used in road under special conditions, Keywords used in appropria...

Keywords used in appropriate technology: Hill Roads : Roads in hilly and mountainous terrain. Landslides : The slippage of mass of hill face. Retaining Walls : Str

Iges application protocol, IGES application protocol: In the year 1977...

IGES application protocol: In the year 1977, the three authors of The Initial Graphics Exchange Specification were identified collectively for their contributions to the growt

Velocity of belt, velocity of belt: velocity of belt passing over the ...

velocity of belt: velocity of belt passing over the driver pulley will decrease Now with this velocity belt pass over driven pulley, Now Velocity of Driven = Velocity

Kinematics, derive an expression for range along iclined palne

derive an expression for range along iclined palne

Computation for the magnitude, A horizontal line ABCD measuring 9m is acted...

A horizontal line ABCD measuring 9m is acted upon by forces of magnitude 400, 600, 400 and 200 N at points A, B, C, D respectively with downward direction. These point are so locat

What is coated electrode, Q. What is coated electrode? These types of e...

Q. What is coated electrode? These types of electrodes are prepared by coating of flux on metal wire. Due to arc metal electrode melts and used as filler metal. Flux melts and

Pmi testing of alloy materials, Q. Show PMI testing of alloy materials? ...

Q. Show PMI testing of alloy materials? Suppliers and Construction Subcontractors are required to verify or conduct PMI testing of alloy materials that they procure and use and

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd