Metallurgical defects-gas porosity, Mechanical Engineering

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.

Posted Date: 9/18/2012 12:42:22 AM | Location : United States







Related Discussions:- Metallurgical defects-gas porosity, Assignment Help, Ask Question on Metallurgical defects-gas porosity, Get Answer, Expert's Help, Metallurgical defects-gas porosity Discussions

Write discussion on Metallurgical defects-gas porosity
Your posts are moderated
Related Questions

hoops stress

What can a valve do?  It can prevent flow (on/off), allow variable control of the flow and provide a safe working environment. What sort of questions should we be asking when selec

Aspects Of Scheduling  The difficulty is a modification of a flexible manufacturing cell at ABB's plant for the manufacturing of turbocharger in Baden, Switzerland. The difficu

Exhaust Manifold : The pipe which connects the exhaust system to the exhaust valve of the engine through which the products of combustion escape into the atmosphere is called the

Difference between SI and CI engines SI engine stands for spark ignition engine while CI engine stands for compression ignition engine. SI engine works on the principle of w

Q. Overall deformation of a component? The overall deformation of a component is a function of the applied load, the materials' creep rate, the maximum in-service temperature,


what type of stresses a thin cell is subjected to?

Find the maximum shear stress at free end: A stepped shaft ABCD, with A is fixed end and D is free end. AB = 1 m, BC = 2 m, CD = 1 m. AB is a hollow shaft of 100 mm outer diam