The Weld Defects #1
1. Undercut
Most structural failures originate from weld joint because it is the source of discontinuity or defects. The most visible weld defect we can easily find in visual inspection is undercut, shown in Figure 1 below. Undercut is usually due to overcurrent in electric arc welding. Overcurrent causes wide melting zone in base metal but not enough weld fusion metal to replace the gap. High lapping speed also leaves the gap poorly filled with weld fusion metal and produces undercut.
To avoid undercut, welder and welding inspector must observe initial weld lap to see whether the current setting is appropriate. Post welding inspection can be tricky since welder can cover undercut by running another lap using lower grade welding electrode and low current. Undercut is dangerous because it amplifies the stress flow due to reduction in section area and stress concentration of the notch form.
Fig. 1. Undercut and overlap.
2. Underfill and Incomplete Joint Penetration
Another visible weld defect is underfill and incomplete joint penetration as shown in Figure 2 below. Underfill is easier to detect and fix. Incomplete joint penetration is also visible if welder and inspector have access to the rear side of the joint. Problem arises when welding a closed structure or structure with limited space so that inspector cannot see the welding quality behind the plate or internal part of the closed structure. This fact should be carefully considered in design and fabrication procedure preparation. If possible, provide internal access such as manhole to allow welder to do 2-side welding, especially when joining thick plates.
Fig. 2. Underfill and incomplete joint penetration.
3. Incomplete Fusion
The third welding defect is incomplete fusion which is due to undercurrent. Arc welding uses concentrated high-temperature electric arc to melt both base metal and welding electrode. These melted base metal and electrode mix and fuse together into weld pool which subsequently bonds adjoining base metals. If the welding current is set too low, ideal melting temperature cannot be achieved and base metal doesn’t melt completely. Furthermore, weld pool material is not adequate and gap between adjoining base metals is not properly filled. This will leave empty holes inside or outside weld joints as shown in Figure 3.
Fig. 3. Incomplete fusion.
4. Defect Detection: Nondestructive Testing
Most incomplete fusion is internal and imperceptible by the eye. Thus, we need Nondestructive Testings (NDT) to check the weld quality. There are many types of NDT, each has its own advantages and limitations. Figure 4 shows a technician performed Magnetic Particle Inspection (MPI) to check a weld joint. Selection of NDT is based on how critical the weld joint is, cost of NDT, detection accuracy, detection depth, etc.
Fig. 4. Magnetic Particle Inspection (MPI).
5. Weld Defect Factor in Design
Most of the time, we should accept and live with the fact that weld defects exist in structures. This should be carefully considered in design phase by giving Fabrication Defect Factor to cover this defect. For example, if we assume there exists undercut with depth 1 mm in 12 mm plates, the remaining strength is (12 – 1)/12 or 0.9167 of original strength. Furthermore this undercut also produces stress concentration factor of, say, 1.2. Thus the remaining strength is now 0.9167/1.2 = 0.7639. Now we have Weld Defect Factor of 1/0.7639 = 1.31. See Design Considerations in Heavy Construction for how to apply this factor in design and calculation.
** End of Article **
Dear sir
It really clear all my doubts about weld defects and their causes and it create me a desire to know more about the spot/mig/tig welding defects and also their reason.
Waiting for your reply.
Thanks & regards
Amit
Amit
December 17, 2006 at 6:18 pm
In actual spot welding prepared for setting the dimension of frame(will be welded), if the dimension follow the drawing or OK, we can continue the process of welding. Spot welding at any point of structure or frame will affect the micro structure by changing of temperature. So there is a welding defect from spot welding but in “small area”. In my experience, I think it’s no problem to reduce cost of jig.
Adi
December 22, 2006 at 4:05 pm
Dear Amit and Adi,
Thanks for your kind responses. I am sorry that I don’t have any experience in Spot Welding, MIG (Metal Inert Gas), or TIG (Tungsten Inert Gas). To try to answer your question, welding is simply melting down metals, joining them and letting them cool and solidify. In the meantime between joining and solidify, we need to protect the reactive molten metal from surrounding.
The commonly used shielded metal arc welding (SMAW) or stick welding use stick which is covered with flux. This flux serves as protective shield during molten state of metals. If it is not protected, steel will easily react with oxygen, especially in outdoor welding, and results in inhibited corrosion, cavity or crack.
In TIG and MIG, instead of using a shielded stick, they use inert gas to protect metals in molten state. Thus, we can say that defects in TIG or MIG will not differ much from the above mentioned defects on stick welding such as: undercut, underfill, incomplete fusion, etc. Additional defects in TIG and MIG may come from the mixture of the protective inert gas. If the inert gas mixture is not properly adjust, then it will produce inhibited corrosion inside the weld.
Spot welding or resistance welding is simply resistance principle in electrical circuit. Arc welding uses the high-temperature electrical arc between 2 NON-CONTACTING metals to melt them. Spot welding uses the high temperature resistance heat between 2 CONTACTING metals to melt them. Thus, spot welding is only effective for joining sheel metals like in automobile body and other thin metals because the weld joint penetration is relatively shallow. If the current is too low, then the defect is incomplete joint.
About Adi response, I think Adi was referring to “tack welding” instead of “spot welding”. Tack weld is small weld used for temporarily holding work specimen during setting and alignment. We know that welding is melting and cooling process which most of the time can tense and twist the specimen due to thermal expansion. Therefore, in order to hold the specimen at their proper place, we need to lock the position with tack weld. Adi was right about reducing cost of jig and fixture. Instead of having a more expensive jig and fixture to hold the work, tack weld is much cheaper and faster.
isadikin
January 15, 2007 at 8:11 am
mr. sadikin
such an inspiring blog for us. please visit us also http://www.reksolindo.co.id. good luck!!
abduh137
October 29, 2007 at 10:23 pm
Hi Pak Abduh. I know Reksolindo. Pack of lecturers from Material Engineering ITB. Thanks for visiting. What is Reksolindo doing now?
isadikin
November 24, 2007 at 1:11 pm
Hi, my name is disman-kl, i like your site and i ll be back
Ivan
November 30, 2007 at 1:36 am
all the welding defects should be submitted with required formulas and photos in brief and also its remedies.
Jatin
January 23, 2008 at 4:34 pm
hello
sir
i am shiva
your web site is very good, but i know about fillet weld defects. but
you not given image of butt weld defects.
shiva
May 13, 2008 at 6:56 pm
hi,
sir, iam arshad khan , i m ndt level 2, i dont have known weld defect ,how to identify defect sir , im wait for your reply ,
thank you,
arshad khan .
mohd_arshad khan
June 24, 2008 at 4:50 pm
gud mrg sir,
this is ramesh, can u send me welding deffects,and how it will come and rectifie the deffects.
ramesh
July 12, 2008 at 12:30 pm
hi,
I am chandra, Send me detail how MIG welding defect takesplace & how it would be rectifi with clear picture.
Chandra jit
August 6, 2008 at 12:03 pm
Dear sir
It really clear all my doubts about weld defects and their causes and it create me a desire to know more about the spot/mig welding defects and also their reason.
Waiting for your reply.
Thanks & regards
abhishek chaturvedi
abhishek chaturvedi
October 13, 2008 at 7:41 pm
hello
thanks for your valuable informations on welding.
my inquiry is about the welding defects and failure , how to prevent and correct.
sincerely,,,,,,,
osman tag elssir
Osman Tag elssir
October 20, 2008 at 1:58 pm
can any one give me an idea about acceptance criteria for UNDERFILL in pipeline as per API-5L SPECIFICATION.WHAT IS THE PERMISSIBLE LENGTH AND DEPTH OF REPAIR FOR UNDERFILL IN PIPELINE AS PER API5L,PSL-2 SPECIFICATIUON?
RAJESH BHAKJHAR
November 29, 2008 at 8:18 am
dear sir im daniel please can u send me the solutions on welding defects: no fusion, incomplete fusion, no penetration, less pentration, blow holes, even gas is there but blow holes are ther
plz give me solutions
thank you!
Daniel
January 22, 2009 at 1:33 pm
Dear Sir,
I am production engineer,
I want to know about weld defects,its causes & remedies or precaution to be taken before weld.
With Regards,
Chirag
chirag
February 6, 2009 at 3:33 pm
Dear Sir
we are welding the steel casting body to steel plate we made DP test on welding surface before fitting, it was 100% DP ok when it is in part. But after welding in outer surface we are finding blow holes developed in casting surface that should be welded inside. we keep on gouzing grinding and DP Testing, but no arrest in defect, it is 120 mm steel casting that should be welded to steel rolled plate. component is MIV disc used in hydel turbines.can you please help
sk raju
February 27, 2009 at 8:42 pm
This site is really informative and educative. It is clarifying many doubts and spreading knowledge on welding which is very much essential for the overall welfare of modern society.
This world must recognize a fact that the present progress is mainly due to development of welding. Similarly, the future of our world also depends only on the knowledge of welding.
Therefore, the people causing the spread of this valuable knowledge must be rewarded suitably since our world cannot survive without welding.
Nori VSN Murthy
April 13, 2009 at 5:54 pm
mr,
i would like to share with u somthing what am getting in my mind.
limitations of SAW welding is the welding position.
in heavy thickness material, like MIG weld viewing (oscillation)can able to apply in SAW welding.
it increases the productivity.
thank u,
gunasegar.k
April 16, 2009 at 1:14 am
I Have no words to appreciate your perfect way of displaying and explainig about the welding defects. I sincerely thank you for the showing the defects with colourful sketches.
Regards,
noorkhan
Qatar
noorkhan
April 17, 2009 at 3:21 pm
Thank you everybody for the kind feedbacks. I am sorry that I cannot be more helpful to all of you. But I will try my best to keep sharing my little knowledge.
isadikin
April 17, 2009 at 8:35 pm
Dear Sir,
Knowledge is like an ocean. It can is made only by little drops. Therefore I sincerely request you to give your valuable knowledge to the people of our mother planet since sharing of knowledge amounts to sharing of wealth and progress essential for everyone on earth. ……. Mr. Nori VSN Murthy, email: norimurthy@sify.com
Mr. NORI VSN MURTHY
May 9, 2009 at 3:20 pm
The scientific, engineering and technological community of our planet must realize and recognize a fact that the term “QUALITY “by itself is meaningless. Secondly – the term quality is subjective and not objective. Lack of understanding of this truth is causing arguments and problems to most of the people connected with quality. The word QUALITY is only a relative term and not an absolute term. As a third point, our planet has ignored this fact. Thus misunderstanding on account of ignorance is also causing great trouble to the people of our planet. Finally, the people of earth must acknowledge a bitter truth that QUALITY is an ultra sensitive balance. Tilting of this balance to any side and by any degree either intentionally or accidentally brings lot of repercussions and, the imbalances if left unnoticed or unchecked ruins several industries of our planet.
Hence, the only way to handle the term QUALITY and also to get rid of the problems and disputes arising out of this word is to QUIT this word by adopting a more meaningful sentence like – “Understanding and meeting the specified requirements of customer “. Since customers all over the world are able to specify their requirements and manufacturers are able to understand them fully and both are able to arrive at a consensus, there shall not be any problem in shifting our engineering and manufacturing activity away from the word quality since this concept is noncontroversial and brings peace and progress to all. Most importantly, adjectives and controversial words like quality must be removed from engineering activity to accelerate the progress essential for the overall well being of our people and our mother planet earth. Otherwise, the people of our planet continue to lose material, money and manpower. ….. Mr. Nori VSN Murthy, Email: norimurthy@sify.com.
Mr. NORI VSN MURTHY
May 9, 2009 at 3:10 pm
Knowledge is like an ocean. It is made only by little drops. Therefore I sincerely request you to give your valuable knowledge to the people of our planet since sharing of knowledge amounts to sharing of wealth and progress that are essential for everyone on earth. ……. Mr. Nori VSN Murthy, email: norimurthy@sify.com
Mr. NORI VSN MURTHY
May 9, 2009 at 3:22 pm
please send me detail of arc welding defect, please mail on my id
thank you
raza
raza
May 11, 2009 at 8:34 pm
dear sir,
can you plese send me more about the welding dfects or if there any web site can i buy from theme i need pictures and acceptable cratieria ofr the defects
thanks
sarmad
May 30, 2009 at 7:29 pm
I am welding flux manufacturern i tried sample flux of F7A2 with EM 12k wire size 2.5mm dia, current parameters are 140Amps with 26V and sped of 1.25Mtrs per minute. what i observed in welding is little sticky on either side on border on weld metal and weld metal serface is not smooth. I would like to know the reseon for the same
jai
June 10, 2009 at 11:32 pm
Your explanations and diagrams is great. Thanks
I would appreciate more typical defects related to Stainless steels and is it regulation to pickle & passivate after welding?
Dicky Lee
July 12, 2009 at 3:37 pm
Dear Sir,
Can you send me more detail about welding defect in my E-Mail ID
Thanks
Palash Ghosh
November 12, 2009 at 7:33 pm
Dear Sir,
Can you send me more detail how we can avoid welding defect.
Thanks
Palash Ghosh
November 12, 2009 at 7:35 pm
useful posting.Thanks
bman
November 23, 2009 at 1:26 pm