How To Prevent Lack Of Fusion In Welding

For proper welding angles follow these steps: To prevent incomplete fusion, place the stringer bead in its proper location at the joint, adjusting the work angle or widening the groove to access the bottom during welding. Keep the arc on the trailing edge of the welding puddle and remember to use a correct gun angle drag of 15 to 45 degrees. Incomplete fusion is a weld defect that occurs when the weld fails to fuse one side of the joint in the root. Find out how to avoide imcomplete fusion. For the best deals on welding machines. In other words, it is a lack of fusion between the base metal and weld metal. A related defect is a lack of penetration which means that fusion has not penetrated deeply enough into the root of the joint. Causes of incomplete fusion: Welding Current too low, Low heat input, Improper weaving; Surface contamination; Electrode angle is incorrect. Incomplete fusion is a lack of penetration or fusion between the weld metal and the parent metal of the piece. Welds with incomplete fusion are weak and substandard welds at best (if not downright dangerous). Here are a few of the most common causes for incomplete fusion, and solutions that will help you avoid the. First, be certain that the base metal and the filler metal are clean and dry. Wipe down the aluminum before welding using a solvent and clean cloth to remove any paint, oil, grease, or lubricants that could introduce hydrocarbons into the weld. Then brush the weld joint with a clean stainless steel brush dedicated for the job.

Welding Defects – Do you know that no matter how you try to keep things in order, but in the end, a mistake will still happen? For example when you casually drive to your campus or workplace, no matter how often you check your car's condition, in one of those days your car will experience a malfunction.

Either your tire blew out or transmission malfunction or even external disturbance like crashes and getting a ticket from patrolling police officer. It seems like there's a force of nature that intervenes to turn things into disorder or chaos. If you think so, know that you're not wrong.

This nature's behavior is called entropy, a behavior that requires us to put extra effort to negate the tendency of things from its disorder state and keeping it in order. That's why you have to regularly check your car and bring that extra tire everywhere you go.

The same force of nature also applies to weld. As a welder, you really want to weld a sound weld. A sound weld means that there's uniformity (with a very little variation tolerance) everywhere you see, either on weld surface or in sub-surface.

A sound weld is the best form of the weld, it will have the ability to withstand its designed stress, which means that the quality of fusion between the weld metal and the parent metal is top-notch. However, entropy also plays its role to spread chaos in welding. If the welder is unaware and somehow make a mistake, it will result in the non-uniform weld metal.

Now, this non-uniform phenomenon is what we call as discontinuity. So what's discontinuity and how to avert the forming of discontinuities during welding? This article will give you a clear definition of discontinuity itself that will surely help you as a welder.

How To Prevent Lack Of Fusion In Welding Equipment

What is Welding Defects ?

Now we know that the existence of discontinuity means that the weldment is not sound. Basically, there are two main categories of discontinuity based on its inflicted damage on the material.

1. Reparable Discontinuity.
   As the name implies, discontinuity under this category is considered harmless to the material that a simple repair action would solve the problem. Most of the mechanical damage such as; scratch, dent, and even surface corrosion falls under this category with the exception a huge dent because you somehow find a way to drop a huge concrete block on it. While welding discontinuities such as; porosity, slag inclusion, and undercut can either called discontinuity or defects.
   Even when this type of discontinuity is highly tolerated. It is wise for you to always avoid it to train your mind to give your best when doing something. So when the time comes for you to handle a job with stricter regulation on discontinuity, you'll be ready.
2. Irreparable Discontinuity.
   In some cases, a discontinuity can greatly affect the performance of the weld. Discontinuities like lack of fusion, laminar tearing, and most forms of cracks are one of them. No matter how hard you try to repair it, you'll only waste your time and resources, making it not worth the fuss. So it's best for you to avoid it from the very first place by following the correct welding procedure.

How to Deal With Discontinuities?

Because there are just so many forms of discontinuity, there are also many ways to treat them. To make things simpler, let's talk about it one by one. Custom inventory pets mod.

Welding Defects :

This is a explain about types of welding defects, pictures, causes, and Remedies.

1. Porosity.

Porosity is one of the classic discontinuity that happens in welding. It happens when there are just so many gas molecules trapped inside during welding. Those gasses might come from a wet electrode because the water molecules on the electrode will dissolve due to the heat of welding and result in trapped oxygen that never comes out until the weld pool turns solid.

A windy environment can also promote porosity because the wind will disrupt the shielding environment around the welding arc and allow gasses to enter the molten metal. This porosity can easily be avoided by avoiding contact with the wet environment during welding and making sure that the weld pool is properly shielded with either flux, gas shielding, or both. Several examination methods can detect porosity such as; visual examination, liquid penetrant, radiography examination, etc.

Causes :

• Air trapped in the shielding gas.
• Flux in the electrode is damp.
• Distance arc welding too length.
• In the welding process which uses shielding gas, the flow rate too high so can make turbulence.

Prevention :

• Use the electrode in good condition (dry) or the box of the electrode is not broken.
• Clean surface of the material from oil and another impurity.
• You must reduce arc length suitable at the welding procedure.
• Use gas flowrate suitable at welding procedure specification.

2. Slag Inclusion.

Slag inclusion is also one of the classic discontinuity that occurs in welding. It's a situation when the slag – a protective layer that supposed to resurface and protect the molten weld pool – is trapped under the geometry of the weld itself.

The trapped slag replaces the supposed filler weld metal with a chunk of Manganese Oxide (may vary) that when you chipped it off will leave the hole gaped, making it good for nothing. The various thing can cause slag inclusion, dirty weld surface, and a relatively low welding parameter being used is supposed to be the primary cause. Detectable visually, but for sub-surface slag inclusion can only be detected by radiography examination or ultrasonic examination.

Causes :

• When cleaning slag in the inter pass is not clean.
• Welding slag melt first in front of a welding arc.
• Slag weld trapped in the weld pool.

Remedies :

• Make sure every inter-run is clean.
• To preventive a slag inclusion, make sure the electrode angle is correct.

3. Undercut Welding Defect.

The undercut is one of the classics, along with slag inclusion and porosity, which occur most in welding. It primarily happens because a bad maneuver is done by the welder that the arc melts the side of the pool without properly filling it.

While it looks minuscule, undercut could be one of the sources of initial crack that later on will propagate and break the material. To avoid this, try to avoid using an overly high welding parameter while moving along the weld bead evenly to avoid traveling too fast. Undercuts are usually surface defects, thus can easily be recognized visually. Liquid penetrant and magnetic particle examination can also help to detect it.

Causes Undercut Welding Defect :

• The welder is not competent when he weaving the electrode.
• The electrode angle is not correct.
• Welding Current too high.
• Incorrect in selecting shielding gas when using the MAG process.

Prevention :

• You must reduce the welding current.
• Use multi-run welding techniques in the flat position.
• Reduce your weaving width or you can change to use multi runs welding.
• When you use the MAG welding process, you can mix gas composition in accordance with material thickness.

4. Cracks.

While there are many causes on which a crack can occur, the crack can also occur during welding, making it worth mentioning. Crack is highly dangerous because it will greatly reduce the material's strength and will propagate along the way when the material is loaded.

Therefore a complete repair procedure should be done at once when the crack is detected by any examination method (radiography, liquid penetrant, and magnetic particle). Some crack can happen during a non-welding process such as lamellar tearing. While cracks like hot and cold crack happen mostly because of welding.

In hot crack, cracks happen because of the pre-existing contaminant like; sulfur and phosphorus inside the base metal. Those contaminants form a carbide that has a lower melting temperature than the base metal itself. When the heat from welding highly increases the temperature, those carbides will melt and decrease the material's strength.

Combined with the stress applied to the material, it will break and propagate fast without even waiting for the material to cool down. Hence the name hot crack. Ordering a killed material can greatly reduce the chance of hot crack to happen, or simply regulating the inter-pass temperature can also work.

A different thing happens in the cold crack, high hydrogen concentration around the weld metal is the primary cause. When the weld metal is hot, the hydrogen in the environment might enter the metal by the mean of diffusion. This hydrogen atom will mostly reside in the HAZ (Heat-Affected Zone) where the crystalline is most susceptible due to its coarseness.

The existence of hydrogen will turn the material into its brittle state that continuously builds internal stress up until its breaking point. This process takes so much time that its breaking point will happen even when everything is already cooled down. Hence the name cold crack. To avoid this, using a low-hydrogen electrode will greatly help, and also doing PWHT (Post Weld Heat Treatment) can reduce the residual stress and also allowing the hydrogen to escape.

5. Tungsten Inclusion.

This type of defect occurs only on welding GTAW. Defects occur due to the melting of tungsten into the weld metal. This defect will be known if we use radiography testing, the defect looks like a light area.

Causes Tungsten Inclusion :

• The Tungsten electrode is in contact with the weld pool during the welding process.
• The hot tungsten electrode is in contact with filler metal.
• Occur crack in the tungsten electrode.
• The use of welding current exceeds the maximum temperature limit of tungsten electrodes.

Remedies :

• Keep the electrode tip distance with the weld pool.
• Make sure the electrode condition is good for use or nothing crack.
• Use the welding current according to the maximum electrode temperature.
• Don't let the hot electrode come into contact with the filler metal

6. Incomplete Penetration.

Welding defects occur in the root area of the weld.

Causes :

• The less welding current.
• The wrong electrode position.
• The electrode movement too fast, and also the diameter of the electrode too large.

Preventive :

• You must increase the welding current suitable in the welding procedure.
• Use the correct diameter electrode suitable with material thickness.

7. Over Spatter.

Spatters can be removed by being grinded or struck using a hammer. Cause of this defect because the current is too large and also a welding arc is too high.

Causes :

• Welding current is too high.
• The arc distance between the electrode and the workpiece is too long.
• Moist flux electrode.
• Gas shielding in the GMAW process 100 CO2.

Preventive :

• Use the correct welding current (see in WPS).
• You must reduce the arc length.
• Before to use, the electrode must be drying in the oven.
• Mixing gas shielding CO2 with Ar.

8. Distortion.

Distortion caused by excessive heat input causing the material to undergo a change in angle.

Causes Distortion :

• Incorrect welding preparation, start from incorrect tack weld.
• Incorrect welding sequence.

Remedies Distortion :

• Before welding, make sure that the material to be connected is straight and the tack weld is strong.
• You must have a qualified welding sequence.

9. Arc Strike.

Arc Strike is a type of welding defects occurring in the material and adjacent to the weld metal. Because welders accidentally touch the electrode to the workpiece area causing the arc strike.

Causes of Arc Strike welding defects:

• Access to the welding groove is difficult.
• The coating of the electrode holder is peeling.
• Wrong laying electrode Holder.
• The clamp at base metal is not good.

Prevention :

• Access to welding should be easier.
• Periodically check the electrode holder.
• Provides a place to put electrode holder.

10. Burn Through.

This occurs at the weld root, this form of welding defects is a hole.

Causes of Burn Through :

• Welding current that is too large.
• Root face and root gap too large.
• The welder is not competent.

Remedies :

• Look at Welding Procedure to setting the correct welding current.
• Welding travel speed must be increase.
• Welding preparation should be correct, you can look at the welding procedure to set the correct size of the root gap and root face
• Welders must be trained.

How To Prevent Lack Of Fusion In Welding Electrodes

See: Definition Of Welding and The History

Conclusion

After we learn that there are just too many variables that may cause a discontinuity. It's just impossible to avoid each and every one of them, so making mistakes every now and then is pretty normal as long as we know how to deal with it.

However, it doesn't mean that we have to take things for granted. We can surely do our best to avoid making mistakes so frequently if we strive. That's what we should do to fight the entropic force of nature, by striving for excellence.

A welding defect is any flaw that compromises the usefulness of a weldment. There is a great variety of welding defects. Welding imperfections are classified according to ISO 6520^[1] while their acceptable limits are specified in ISO 5817 ^[2] and ISO 10042.^[3]

Major causes[edit]

According to the American Society of Mechanical Engineers (ASME), causes of welding defects can be broken down as follows: 41 percent poor process conditions, 32 percent operator error, 12 percent wrong technique, 10 percent incorrect consumables, and 5 percent bad weld grooves.^[4]

Hydrogen embrittlement[edit]

Residual stresses[edit]

The magnitude of stress that can be formed from welding can be roughly calculated using:^[5]

EαΔT{displaystyle Ealpha Delta T}

Where E is Young's modulus, α is the coefficient of thermal expansion, and ΔT is the temperature change. For steel this calculates out to be approximately 3.5 GPa (510,000 psi).

Types[edit]

Cracks[edit]

Defects related to fracture.

Arc strikes[edit]

An Arc Strike is a discontinuity resulting from an arc, consisting of any localized remelted metal, heat affected metal, or change in the surface profile of any metal object. ^[6]Arc Strikes result in localized base metal heating and very rapid cooling. When located outside the intended weld area, they may result on hardening or localized cracking, and may serve as potential sites for initiating fracture. In Statically Loaded Structures, arc strikes need not be removed, unless such removal is required in contract documents. However, in Cyclically Loaded Structures, arc strikes may result in stress concentrations that would be detrimental to the serviceability of such structures and should be ground smooth and visually inspected for cracks. ^[7]

Cold cracking[edit]

Residual stresses can reduce the strength of the base material, and can lead to catastrophic failure through cold cracking. Cold cracking is limited to steels and is associated with the formation of martensite as the weld cools. The cracking occurs in the heat-affected zone of the base material. To reduce the amount of distortion and residual stresses, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments.^[8]

Cold cracking only occurs when all the following preconditions are met:^[9]

• susceptible microstructure (e.g.martensite)
• hydrogen present in the microstructure (hydrogen embrittlement)
• service temperature environment (normal atmospheric pressure): -100 to +100 °F
• high restraint

Eliminating any one of these will eliminate this condition.

Crater crack[edit]

Crater cracks occur when a welding arc is broken, a crater will form if adequate molten metal is available to fill the arc cavity.^[10]

Hat crack[edit]

Hat cracks get their name from the shape of the cross-section of the weld, because the weld flares out at the face of the weld. The crack starts at the fusion line and extends up through the weld. They are usually caused by too much voltage or not enough speed.^[10]

Hot cracking[edit]

Hot cracking, also known as solidification cracking, can occur with all metals, and happens in the fusion zone of a weld. To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized.^[8] Other causes include too high welding current, poor joint design that does not diffuse heat, impurities (such as sulfur and phosphorus), preheating, speed is too fast, and long arcs.^[11]

Underbead crack[edit]

An underbead crack, also known as a heat-affected zone (HAZ) crack,^[12] is a crack that forms a short distance away from the fusion line; it occurs in low alloy and high alloy steel. The exact causes of this type of crack are not completely understood, but it is known that dissolved hydrogen must be present. The other factor that affects this type of crack is internal stresses resulting from: unequal contraction between the base metal and the weld metal, restraint of the base metal, stresses from the formation of martensite, and stresses from the precipitation of hydrogen out of the metal.^[13]

Longitudinal crack[edit]

Longitudinal cracks run along the length of a weld bead. There are three types: check cracks, root cracks, and full centerline cracks. Check cracks are visible from the surface and extend partially into the weld. They are usually caused by high shrinkage stresses, especially on final passes, or by a hot cracking mechanism. Root cracks start at the root and extent part way into the weld. They are the most common type of longitudinal crack because of the small size of the first weld bead. If this type of crack is not addressed then it will usually propagate into subsequent weld passes, which is how full cracks (a crack from the root to the surface) usually form.^[10]

Reheat cracking[edit]

Reheat cracking is a type of cracking that occurs in HSLA steels, particularly chromium, molybdenum and vanadium steels, during postheating. The phenomenon has also been observed in austenitic stainless steels. It is caused by the poor creep ductility of the heat affected zone. Any existing defects or notches aggravate crack formation. Things that help prevent reheat cracking include heat treating first with a low temperature soak and then with a rapid heating to high temperatures, grinding or peening the weld toes, and using a two layer welding technique to refine the HAZ grain structure.^[14][15]

Root and toe cracks[edit]

A root crack is the crack formed by the short bead at the root(of edge preparation) beginning of the welding, low current at the beginning and due to improper filler material used for welding. The major reason for these types of cracks is hydrogen embrittlement. These types of defects can be eliminated using high current at the starting and proper filler material. Toe crack occurs due to moisture content present in the welded area, it is a part of the surface crack so can be easily detected. Preheating and proper joint formation is a must for eliminating these types of defects.

Transverse crack[edit]

Transverse cracks are perpendicular to the direction of the weld. These are generally the result of longitudinal shrinkage stresses acting on weld metal of low ductility. Crater cracks occur in the crater when the welding arc is terminated prematurely. Crater cracks are normally shallow, hot cracks usually forming single or star cracks. These cracks usually start at a crater pipe and extend longitudinal in the crater. However, they may propagate into longitudinal weld cracks in the rest of the weld.

Distortion[edit]

Welding methods that involve the melting of metal at the site of the joint necessarily are prone to shrinkage as the heated metal cools. Shrinkage then introduces residual stresses and distortion. Distortion can pose a major problem, since the final product is not the desired shape. To alleviate certain types of distortion the workpieces can be offset so that after welding the product is the correct shape.^[16] The following pictures describe various types of welding distortion:^[17]

• Transverse shrinkage

• Angular distortion

• Longitudinal shrinkage

• Fillet distortion

• Neutral axis distortion

Gas inclusion[edit]

Gas inclusions is a wide variety of defects that includes porosity, blow holes, and pipes (or wormholes). The underlying cause for gas inclusions is the entrapment of gas within the solidified weld. Gas formation can be from any of the following causes- high sulphur content in the workpiece or electrode, excessive moisture from the electrode or workpiece, too short of an arc, or wrong welding current or polarity.^[12]

Inclusions[edit]

There are two types of inclusions: linear inclusions and rounded inclusions. Inclusions can be either isolated or cumulative. Linear inclusions occur when there is slag or flux in the weld. Slag forms from the use of a flux, which is why this type of defect usually occurs in welding processes that use flux, such as shielded metal arc welding, flux-cored arc welding, and submerged arc welding, but it can also occur in gas metal arc welding. This defect usually occurs in welds that require multiple passes and there is poor overlap between the welds. The poor overlap does not allow the slag from the previous weld to melt out and rise to the top of the new weld bead. It can also occur if the previous weld left an undercut or an uneven surface profile. To prevent slag inclusions the slag should be cleaned from the weld bead between passes via grinding, wire brushing, or chipping.^[18]

Isolated inclusions occur when rust or mill scale is present on the base metal.^[19]

Lack of fusion and incomplete penetration[edit]

Lack of fusion is the poor adhesion of the weld bead to the base metal; incomplete penetration is a weld bead that does not start at the root of the weld groove. Incomplete penetration forms channels and crevices in the root of the weld which can cause serious issues in pipes because corrosive substances can settle in these areas. These types of defects occur when the welding procedures are not adhered to; possible causes include the current setting, arc length, electrode angle, and electrode manipulation.^[20] Defects can be varied and classified as critical or non critical. Porosity (bubbles) in the weld are usually acceptable to a certain degree. Slag inclusions, undercut, and cracks are usually unacceptable. Some porosity, cracks, and slag inclusions are visible and may not need further inspection to require their removal. Small defects such as these can be verified by Liquid Penetrant Testing (Dye check). Slag inclusions and cracks just below the surface can be discovered by Magnetic Particle Inspection. Deeper defects can be detected using the Radiographic (X-rays) and/or Ultrasound (sound waves) testing techniques.

Lamellar tearing[edit]

Lamellar tearing is a type of welding defect that occurs in rolledsteel plates that have been welded together due to shrinkage forces perpendicular to the faces of the plates.^[21] Since the 1970s, changes in manufacturing practices limiting the amount of sulfur used have greatly reduced the incidence of this problem.^[22]

Lamellar tearing is caused mainly by sulfurousinclusions in the material. Other causes include an excess of hydrogen in the alloy. This defect can be mitigated by keeping the amount of sulfur in the steel alloy below 0.005%.^[22] Adding rare earth elements, zirconium, or calcium to the alloy to control the configuration of sulfur inclusions throughout the metal lattice can also mitigate the problem.^[23]

Modifying the construction process to use casted or forged parts in place of welded parts can eliminate this problem, as Lamellar tearing only occurs in welded parts.^[21]

Undercut[edit]

Undercutting is when the weld reduces the cross-sectional thickness of the base metal and which reduces the strength of the weld and workpieces. One reason for this type of defect is excessive current, causing the edges of the joint to melt and drain into the weld; this leaves a drain-like impression along the length of the weld. Another reason is if a poor technique is used that does not deposit enough filler metal along the edges of the weld. A third reason is using an incorrect filler metal, because it will create greater temperature gradients between the center of the weld and the edges. Other causes include too small of an electrode angle, a dampened electrode, excessive arc length, and slow speed.^[24]

References[edit]

1. ^BS EN ISO 6520-1: 'Welding and allied processes — Classification of geometric imperfections in metallic materials — Part 1: Fusion welding'(2007)
2. ^BS EN ISO 5817: 'Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) — Quality levels for imperfections' (2007)
3. ^BS EN ISO 10042: 'Welding. Arc-welded joints in aluminium and its alloys. Quality levels for imperfections' (2005)
4. ^Matthews, Clifford (2001), ASME engineer's data book, ASME Press, p. 211, ISBN978-0-7918-0155-0.
5. ^Bull, Steve (2000-03-16), Magnitude of stresses generated, University of Newcastle upon Tyne, archived from the original on 2009-12-06, retrieved 2009-12-06.
6. ^AWS A3.0: 2020 - Standard Welding Terms and Definitions
7. ^aisc.org/steel-solutions-center/engineering-faqs/8.5.-repairs
8. ^ ^abCary & Helzer 2005, pp. 404–405.
9. ^[1] A Brief MIG welder Troubleshooting Guide
10. ^ ^abcRaj, Jayakumar & Thavasimuthu 2002, p. 128.
11. ^Bull, Steve (2000-03-16), Factors promoting hot cracking, University of Newcastle upon Tyne, archived from the original on 2009-12-06, retrieved 2009-12-06.
12. ^ ^abRaj, Jayakumar & Thavasimuthu 2002, p. 126.
13. ^Rampaul 2003, p. 208.
14. ^Bull, Steve (2000-03-16), Reheat cracking, University of Newcastle upon Tyne, archived from the original on 2009-12-07, retrieved 2009-12-06.
15. ^Bull, Steve (2000-03-16), Reheat cracking, University of Newcastle upon Tyne, archived from the original on 2009-12-07, retrieved 2009-12-06.
16. ^Weman 2003, pp. 7–8.
17. ^Bull, Steve (2000-03-16), Welding Faults and Defects, University of Newcastle upon Tyne, archived from the original on 2009-12-06, retrieved 2009-12-06.
18. ^Defects/imperfections in welds - slag inclusions, archived from the original on 2009-12-06, retrieved 2009-12-05.
19. ^Bull, Steve (2000-03-16), Welding Faults and Defects, University of Newcastle upon Tyne, archived from the original on 2009-12-05.
20. ^Rampaul 2003, p. 216.
21. ^ ^abBull, Steve (2000-03-16), Welding Faults and Defects, University of Newcastle upon Tyne, archived from the original on 2009-12-04.
22. ^ ^abStill, J. R., Understanding Hydrogen Failures, retrieved 2009-12-03.
23. ^Ginzburg, Vladimir B.; Ballas, Robert (2000), Flat rolling fundamentals, CRC Press, p. 142, ISBN978-0-8247-8894-0.
24. ^Rampaul 2003, pp. 211–212.

Bibliography[edit]

• Cary, Howard B.; Helzer, Scott C. (2005), Modern Welding Technology, Upper Saddle River, New Jersey: Pearson Education, ISBN0-13-113029-3.
• Raj, Baldev; Jayakumar, T.; Thavasimuthu, M. (2002), Practical non-destructive testing (2nd ed.), Woodhead Publishing, ISBN978-1-85573-600-9.
• Rampaul, Hoobasar (2003), Pipe welding procedures (2nd ed.), Industrial Press, ISBN978-0-8311-3141-8.
• Moreno, Preto (2013), Welding Defects (1st ed.), Aracne, ISBN978-88-548-5854-1.
• Weman, Klas (2003), Welding processes handbook, New York, NY: CRC Press, ISBN0-8493-1773-8.

External links[edit]

How To Avoid Lack Of Penetration In Welding