Weld-porosity,

Know Where it Comes From.

SOLUTIONS with Effective, Practical Advice

How Holes form in Welds?

Welding Problem? Solve it! with
Help from a Welding Professional
Contact Us.

Note: To view Google Ads, Pls.
Right Click and
Open in a New Window.
Weld-porosity is a common form of discontinuity.

Holes and Pores can be found in Fusion Welding and also in Resistance Spot or Seam Welding.

Porosity is characterized by form, by location, by importance, by orientation, by origin, and by method of detection.

Discontinuity, as defined in AWS A3.0, is an interruption of the typical structure of a material in its mechanical, metallurgical or physical characteristics.

Where does Weld-porosity come from?

Typically porosity is a limited space devoid of metal where gas was trapped during solidification.

Weld-porosity consists in spherical or elongated cavities or voids, normally described by the following types.

Scattered porosity occurs where several pores of different sizes are distributed irregularly in the volume of the weld metal.

The cause is generally attributed

  • to faulty welding technique,
  • to incorrect shielding gases, insufficient or contaminated or
  • to materials improperly or incompletely cleaned from various contaminants.

Cluster porosity has pores grouped locally with irregular distribution, deriving frequently from faulty start or stop of welding arc, or from arc blow.

Piping porosity is described as cavities longer than their width, generally at right angle from the weld face.

If it is present in the volume, it may or may not appear on the surface. It is caused by too rapid solidification.

Elongated porosity is similar to the one just here above but its orientation is parallel to the weld axis.

Finally Aligned or Linear porosity, shows pores more or less along a line, at certain locations within a weld or along a weld interface or boundary.

Besides these types also elongated pores or Wormholes are described, indicating a large amount of gas being locked in the solidified weld metal.

Weld-porosity in weld metals is caused by gases entrapped in the solidifying weld metal.

The origin can be contamination or poor protection of the molten solidifying metal.

Gases like hydrogen, oxygen and nitrogen have a larger solubility in molten metal than in the solid phase.

Therefore during weld cooling, gases are expelled from the solidifying melt.

They become trapped if solidification occurs before they reach the surface.

The gas Carbon monoxide (CO), a reaction product of oxygen and carbon is more likely than oxygen to cause Weld-porosity.

Moisture from inadequately dried electrodes, fluxes or work piece surface, and organic products like grease and oil on work piece surfaces are the main sources of hydrogen, principal cause of Weld-porosity in Al Cu, Ti, Mg.

In steel welds, hydrogen is more likely to cause cracking (see Hydrogen Embrittlement) rather than porosity.

Nitrogen from air causes Weld-porosity in carbon steel, stainless steel and nickel in GMAW (Mig) welding.

Note: To view Google Ads, Please
Right Click and
Open in a New Window.

Dryness and cleanliness are the most important precautions to be always adopted.

Poor (contaminated) shielding gas quality, insufficient or excessive flow dragging air, may contribute to weld oxidation and Weld-porosity, as well as any poor maintenance condition of welding torch, gun, or hoses.

Finally one should monitor welders' skill and technique.

Improper manipulation of electrode, torch or gun, and excessive arc length, electrode extension, or travel speed, may all increase Weld-porosity.

The importance of the Weld-porosity actually present in welded work pieces will determine the acceptability of welded fabrications in accordance with the specific requirements.

Porosity visible on the surface by visual examination is often indicative of a larger presence thereof below the surface.

An Article on Weld Quality Monitoring was published (3) in Issue 137 of Practical Welding Letter for January 2015.
Click on PWL#137 to see it.

The nondestructive test methods most used for finding and evaluating the presence of Weld-porosity are volume scanning techniques, mainly ultrasonic and radiographic testing (see Welding Inspection).

Two Resource Bulletins were dedicated to these subjects:

Bulletin 6 of Mid October 2006 on Radiography
Click on PWL#038B.

Bulletin 49 of Mid May 2010 on Ultrasonic NDT
Click on PWL#081B.

The evaluation of the level of the discontinuities is based on comparison with Reference Blocks (for Ultrasonics) and with Reference Radiographs (for Radiography).

In the common industrial practice the facilities and the inspectors for examining and approving welding productions, must be certified by recognized authorities as being competent and adequate to their responsible task

For additional insight see the following Article:
Porosity Problems in GMAW Welds
http://www.esabna.com/us/en/education/knowledge/qa/porosity-problems-in-gmaw-welds.cfm

ASTM E390-11
Standard Reference Radiographs for Steel Fusion Welds
ASTM International / 01-Aug-2011 / 4 pages

ASTM RRE0390CS [Complete Set]
Adjunct to E390 Reference Radiographs for Steel Fusion Welds
ASTM International /

ASTM RRE039001
Adjunct to E 390 Volume I -- Reference Radiographs for Steel Fusion Welds
Vol I -- 16 plates, to 1/4 in.
ASTM International /

ASTM RRE039002
Adjunct to E 390 Volume II -- Reference Radiographs for Steel Fusion Welds
Vol II -- 29 plates, Over 1/4 - 3 in.
ASTM International /

ASTM RRE039003
Adjunct to E 390 Volume III -- Reference Radiographs for Steel Fusion Welds
Vol III -- 32 plates, Over 3 - 8 in.
ASTM International /

Watch the following Video

Preventing Porosity in Aluminum Welding

http://www.youtube.com/watch?v=Yu3BtdERmFM

* * *
Any questions or comments or feedback? Write them down and send them to us by e-mail. Click on the Contact Us button in the NavBar at top left of every page.

Hardness Testing
made simple Let us remind you that, if you are interested, we offer a no cost subscription to our Practical Welding Letter and a bonus book in pdf format to be made available for download to your computer on the subject of
PRACTICAL HARDNESS TESTING MADE SIMPLE.
Click on Subscription.

To reach a Guide to the collection of the most important Articles from Past Issues of Practical Welding Letter, click on Welding Topics.

Note: To view Google Ads, Please
Right Click and
Open in a New Window.

Back Home
QUALITY
Site Map

Welding Standards
Welding Control
Welding Testing
Welding Qualification
Welding Inspection
Brazing Inspection
Weld Macro
Welding Distortion
Welding Defects
Welding Failures
Weld Cracking
Welding Liability
Weldability Testing
Visual Weld Inspection
Welding Validation



If you did not yet find what you need, why not typing your question in the following Search Box?


How can you solve
your Welding Problems?

Click on Welding Consultation and
Metallurgical Expertise.

Weld-porosity Top



Watch the following Video...

Click on the following image to watch the SBI! TV Show!

SBI TV Show

BUILT BY:

Solo Build It!

Click on this Logo NOW!


Watch - The Video:

Why Don't I Work From Home?

and also

Think outside the Cube.

Follow this Invitation!

Experience C2 power and flexibility in action by clicking SBI! 2.0 For You.
Where SBIers share their business-building experiences first-hand.
You will realize that there is nothing comparable to SBI! when you read
real stories from SBIers who share how C2 has helped them
expand, accelerate, build trust and monetize their sites.

Follow SiteSell and you will be amazed...

SiteSell Facebook
http://facebook.sitesell.com/Quark.html

SiteSell Twitter
http://twitter.sitesell.com/Quark.html

On SiteSell Twitter, visitors will learn who SiteSell is, through each person delivering personal insights into SiteSell... his news, his interests and perspectives. They can interact with each "SiteSeller" too, asking questions of programmers, coaches or anyone else.

SiteSell YouTube
http://youtube.sitesell.com/Quark.html

SiteSell Blog
http://blogit.sitesell.com/Quark.htm

Copyright (©) 2011, 2012, 2013, 2014, 2015, 2016, 2017
by Elia E. Levi and www.welding-advisers.com
All Rights Reserved

SBI!