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Welding-defectsto avoid and correct:SOLUTIONS with Effective, Powerful AdviceIs any minor flaw a defect?

Welding-defects, weld discontinuities, visual welding defects, internal welding defects,welding cracks, porosity, dimensional defects, deformations, incomplete fusion or

penetration, nonmetallic inclusions, dangerous weld microstructures, causes and

prevention, useful links, welding defect free tips, joining questions needing answers:

these are some of the items developed in this Site page for the benefit of interested

readers.

What is in here for me?

In a previous page on WELDING FAILURES, we expressed the opinion that failures occur only

in service. We imply by this that Welding-defects should not be allowed out of the production

line. But human activities being what they are, it is probably unrealistic to exclude at all the

chance that from time to time defective structures be put into service. It is however under the

responsibility of the person in charge of a welding operation to strive to reduce such occurrences

to the minimum.

Important AnnouncementFor assembling at no cost your own Encyclopedia Online,

a rich collection of valuable information from expert Internet Sources,

on

Materials, Volume 1,and Metals Welding, Volume 2,

is now available.

See our New Page on Metals Knowledge

What are Welding-defects?

They are excessive conditions, outside the acceptance limits, which risks to

compromise the stability or the functionality of the welded structure. They are alsocalled rejectable discontinuities. This means that the same type of discontinuity of alesser degree, might be considered harmless and acceptable.Are there acceptable Welding-defects? No, by definition a defect is rejectable. Therecan be acceptable discontinuities. The designer, or the purchaser, or the person incharge of the welding project is entitled to define the limits of acceptance. And theselimits are valid only for the application and the usage involved.Are there undetected defects? Hopefully not! No Welding-defects should go undetected,but undetectable discontinuities yes, that are acceptable, as defined by the designer.What should be done when Welding-defects are detected? One should reject the items

and put them temporarily on hold. One should determine the cause and try to implementa corrective action to avoid future recurrence. Then an authorized professional shoulddetermine if the defects are repairable or not. If yes by which procedure. Standardprocedures may be approved for routine application.
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An Article on Failures from weld Discontinuities is included in our Practical Welding Letter No.

11 of July 2004. To read the article click on PWL#011.

An Article including considerations on Weld Defects and on the importance of investigating the

reasons of their appearance for eliminating their recurrence was published in Issue 28 of

Practical Welding Letter for December 2005. To read the article (in Section 2) click onPWL#028.

An article of ours, was published on July 11, 2006. It can be found by clicking on Arc

Welding Discontinuities.An Article on Lamellar Tearing was published (7) in Issue 46 of Practical Welding

Letter for June 2007.Click on PWL#046 to read it.

To receive all the issues of PWL as they are published, click on Subscription.

Definitions...

What is the difference between discontinuities and Welding-defects? A discontinuity isan objective lack of material, an interruption in the physical consistence of a part.Examples are cracks, seams, laps, porosity or inclusions. It may or may not beconsidered a defect depending if it its presence endangers or not the integrity, theusefulness and the serviceability of the structure.By knowing what is likely to produce Welding-defects one should learn how to avoidthem. It is essential to distinguish discontinuities from harmful defects. Productionwithout defects saves worktime, materials, repair costs, decrease in productivity.Excessive defect production indicates some basic condition affecting the operationwhich should be investigated and corrected.Causes for rejection and how to avoid Welding-defects.

Avoidance of Welding-defects starts with correct design and preparation. This may lookas an obvious statement but somehow it is a more frequent than desired situation.There is no point in trying to correct by welding for misalignment or for improper set upof the workpiece. There is no gain in time, really, only an increased probability ofproducing Welding-defects and of spending time and resources in trying to repair thewelded item.Also the use of recommended tools and fixtures should be implemented with noexcuses admitted for temporary unavailability. The required means, in good operationalcondition, should be used with the correct parameters, according to the approvedprocedure. If the welding procedure is incapable of ensuring defect free implementation,then it should be improved upon.

The welder or the machine operator should be proficient in the process

selected and all physical accessories assigned should be ready for use.

Among them, aspirators of fumes, fan to circulate air, screens toprotect other workers nearby, etc.

If electrodes need be dried, so they should be. Cleaning of fixtures and

workpiece should be performed before setting up. A last touch up may

be repeated just before welding.

Types of Welding-defects.

DIMENSIONAL Welding-defects can be assessed by visual inspection and bymeasuring with simple weld gages. They derive from improper set up or by distortionwhich should be controlled in a proper fixture, or by a different welding sequence. In
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general they should be corrected by employing proper means before welding.MISALIGNMENT is a setup problem.Other appearance features which may cause rejection of these Welding-defects areexcessive bead convexity and reinforcement, or the opposite condition, namelyconsiderable concavity and undersized welds. Here the welder's technique should be

improved.UNDERCUT consists in a groove formed into the base metal, adjacent to the weldbead. It derives from improper manipulation of torch or electrode. Further training andimproved skill of the welder should save future performance.CRACKS are Welding-defects never permitted, because they are seen as stressraisers, and capable to grow until fracture. Different forms and positions of cracks canhint at their origin, and should be investigated before trying to correct for theirappearance. Except for cases of lack of experience of the welder, who may be unableto end a weld bead without crater cracking, other instances derive mostly from limitedweldability of the materials, and should be dealt with by whoever has metallurgicalexperience, by means of special procedures invoking pre-heat and post heat and other

tricks which the welder cannot be expected to provide.Fine cracks that cannot be seen by visual inspections, are the object of specialized

inspection techniques. See NON DESTRUCTIVE TESTING in WELDINGINSPECTION.

More Welding-defects...POROSITY is a condition caused by gases remaining entrapped in the melt. Thispertains generally to internal Welding-defects, which can be detected either bysectioning (which is a destructive test) or by special non destructive testing likeradiography or ultrasonic testing. If this condition is determined, one should eliminate

the cause, be it the material, or humidity in the electrode sheathing, or gases fromexcessive heat and turbulence in the melt or incorrect manipulation (improve skill).Among other important Welding-defects one should strive to eliminate the following.

INCOMPLETE FUSION, which is generally assessed by sectioning the joint (mostly atest piece) and finding the unmelted base metal that outlines the original jointshape.And INADEQUATE PENETRATION that means that the weld bead extends fromits face only to a limited distance, less than what is required by the procedure.

NON METALLIC INCLUSIONS (in Shielded Metal Arc Welding) usually refer to

Welding-defects in the form of slag being trapped in the melt, generally meaning

insufficient skill of the welder. It could also mean oxide inclusion, in all types ofwelding, or tungsten metal, in Gas Tungsten Arc Welding. All these conditions can be

detected either in a section or by non destructive inspection techniques.

RESISTANCE WELDING has its own set of unacceptable Welding-defects per

Specification, to be determined at the stage of schedule approval by destructive testing.

Shear Strength, a common Specification requirement, is determined by mechanical

testing of spot welded coupons. The shape and dimensions of the weld nugget, and the

appearance of Welding-defects in the form of internal cracks or inadequate fusion can

only be determined in a section by destructive examinations of cut up specimens, ground,

polished and etched, under a microscope.At the production stage one should put the utmost care in manufacturing acceptable joints

because it is the least expensive solution. Most of the Welding-defects are visible. The welder
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should be encouraged to inspect his/her own weld. Inexperienced welders should be asked to

seek advice from more skilled fellow workers, and to look for help for repair in order to avoid

just a cover up.

Failures in service can come up for reasons different from manual welder's skill. But this is

another subject that is being dealt with in a page onWELDING FAILURES

NEW RESOURCES

Find some interesting links in a special Mid MonthBulletin Page of our PRACTICAL WELDING LETTER,designed offer you, our interested readers, theopportunity to search the web quickly and effectivelyon the subject of Welding Failures and relatedSubjects.

We urge you to explore this rich source of essential

knowledge.

Online Resources on Failure Analysis, Root CauseDetermination, Physical Survey, EvidenceCollection, Witness Information, MetallurgicalInvestigation, presenting Articles, Downloads, Linksand Information is now available by clicking onPWL#053B.

See also the Special Mid Month Bulletin 20 listing Online Resources

on Welding Defects, Welding Discontinuities, Types of Defects,Visual and Dimensional Defects, Internal Defects, Finding and

Repairing Defects and more...

Click on Bulletin 20.

Looking for more Online Reference Links? Click on WeldingResources

* * *

Any questions or comments or feedback? Writethem down and send them to us by e-mail. Click on

the Contact Us button in the NavBar at top left of

every page.

Have you already subscribed to your FREE copy of

Practical Welding Letter and downloaded your FREE

copy of our booklet in pdf format on PRACTICALHARDNESS TESTING MADE SIMPLE? If not yet, just

click here for your PWL Subscription.
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You might find a few items interesting to you, related to your welding

activity.

To reach a Guide to the collection of the most important Articles

from Past Issues of Practical Welding Letter, click on Welding Topics.

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All Rights Reserved.

Welding-defects are the worst enemies of successful production.

Considerable effort should be spent to learn to detect and avoid them.

Look here...
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