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12 Quality Testing Methods to Help you Identify Good Welds

In this blog post, you’ll read:This article intends to tell you how to identify the good weld and bad weld, furthermore, it lists the root cause that leads to the bad weld, and how to make good welds.

Table of Contents

What is a Good Weld?  

  • A good weld is a strong, defect-free, aesthetically pleasing connection between two components. This type of weld has the potential to last a long time. Incidentally, in some fields of application, welds are called connections or joints.
  • A good weld is one that is ready for use. No additional finishing or other steps are required. The joints of this weld are smooth and neat. It has the optimal appearance which is superior to other welds of its kind.
  • A good weld  is one that meets standards and requirements which are set by scientists, engineers, and users.
  • A good weld is also a smart investment. It has no defects or weaknesses that can make it prone to failure. This type of connection lasts long, performs well when used, and saves money in repairs.


What does a Good Weld Look Like? 

good weld

It is easy to tell that this is a good weld. First, a good weld is a uniform. There is no variation in the bead height, width, and shape.

Also, there are no gaps or voids in the weld joint. The finish of a good weld will be smooth to the touch without any variations in texture that would result from inconsistencies in the casting surface. There will also not be any cracks on the surface of a good weld.

Besides, a good weld has a consistent thickness. This simply means that the thickness of the weld is uniform from end to end of the weld.

A good weld will also have no undercutting, which results in less spatter and it has minimal porosity (see section II below on how to inspect for porosity).

Another feature of a good weld is done with a clean flame and there are no slag deposits or flux residue left behind that may require further cleaning.

In addition, you will not see any spatter drops on the weld. These drops are an indication that the welder was sloppy and not paying attention to what he/she is doing. Probably they used bad welding techniques.

If the joints are safe and reliable: Take your time to inspect the joints of the weld. Do they look strong and reliable? Are they safe to use in their intended work? The connections at the joints are another sign of quality weld.


What are the Popular Welding Procedures Types?  

To be able to identify good and bad welds, it will only be prudent that we look at the different types of welds. From there you will be in a position to tell whether the workmanship is bad welds or quality welds

Here are the most common methods of welds:

 – MIG Welding (or GMAW)

Mig Welding


MIG stands for Metal Inert Gas welding. This is a process that uses a welding machine and gas to melt the metal. This method is commonly used in both manufacturing and repair works.

The MIG welding process entails the following:

Welding wire is fed into the welding gun until it becomes a molten state. When this happens, the welder passes the metal piece to be welded. At the same time, argon gas is being directed towards the tip of the wire feeder. The tip of the wire will then melt and join with both pieces of metals. 

Before we move on, it will be good for you to know that there are two types of MIG welding processes; traditional or manual and semi-automatic. 

Both types have their pros and cons but they are equally effective in terms of giving quality welds.

MIG method is mainly used on thin sheet metal alloys such as stainless steel and aluminum sheets.


 – TIG welding (or GTAW)


TIG Welding


TIG stands for Tungsten Inert Gas Welding process (electric ). It involves the use of a tungsten electrode to melt and weld both pieces of metals. The process is done under an electrical current with shielding gas (usually argon).

It uses a tungsten electrode which is a metal that can support extreme heat. It also produces little spatter during the process.

TIG welding is used on both ferrous and non-ferrous metals such as copper and magnesium.


 – Stick-Shielded Metal Arc Welding (or SMAW)

Stick-Shielded Metal Arc Welding


This process uses an electric arc to melt both pieces of metals using shielding gas( usually argon ). This process mainly uses two types of electrodes:  stick electrodes and flux-cored ones. Stick electrodes are used in manual processes while the flux core one is used by automated systems. 

Both these variations use electric current to create heated up from where it creates molten metal and welds them together. 


 – Plasma Arc Welding


Plasma Arc Welding


This is also referred to as cutting electric arc welding technology because wires are used for insertion at low speed. The plasma arc process uses plasma torches, which are flexible, to cut both pieces of metal. This method is mainly used on thin sheets of metal that cannot be reached by any other welding methods. 

Plasma arc and plasma cutting technology are both similar when it comes to producing clean cuts on the surface of metal sheets. 


 – Oxy welding

Oxy welding


This is also known as oxyacetylene welding.  This method of welding uses oxygen and acetylene gas to create a high temperature during the process. This type is usually used for manufacturing metallic products that are relatively small in sizes such as fenders, connectors, and shelves.   


Good Weld vs Bad Weld?

– Characteristics of good welds

Here are the most outstanding characteristics of a good weld:

*No cracks or holes: this is the single most important thing to look for in a weld, whether you are purchasing a car or anything else really. Bad welds tend to form cracks and holes. If you see any signs of this you should be extra cautious about buying that piece of art.


*Good color: seems obvious, but not all good welds are colored. Bad ones on the other hand can have very noticeable color differences with so-called “burn marks” around them. Badly done welding tends to burn the metal around it, which means there are some issues with your welder.


*Smooth edges: The edges of a well-done weld will either be perfectly smooth. Bad welds have rough and jagged edges. Bad welders don’t know how to properly heat a surface or very poor quality equipment.


*No slag: Bad welds often have “slag” on them, which is basically just the burnt residue from the metal being heated up and melted. It forms a layer over the weld making it look like cheap work (which it most likely is).


*Uniform dimensions: Bad welds have bigger and/or irregular dimensions than the good ones. The product has a uniform length, width, and height.


*Thickness of Weld: Bad welds tend to be thinner than the originals. Good welds, on the other hand, are thicker and feature some elements or robustness.


*No under-welding: A bad welder won’t go deep enough into the piece he is welding and will end up “under-welding” it, which means it won’t be as strong or durable.


* Strong joints or connections: poor welding tends to show a lack of skill when building a connection, whereas good workmanship will take you hours longer to spot because they have been properly prepared with slots and notches before being joined together. 


– Characteristics of a bad weld

Bad welds


*Cracks: Bad welds tend to crack with time. The bad or unqualified welder uses lower quality metals making the weld weak and prone to cracking


* Bad appearance: Welds made by unqualified people can look messy, uneven, and inconsistency 


* Excess Spatter: Bad welding creates excess spatter especially when an improper filler rod is used. When this happens, you will find metal chips at the base of the weld that could cause rusting when in contact with water


* Bad penetration: Bad welds tend to have a bad penetration since an unqualified welder tends to rush through and end up with a poor quality of the weld. Bad penetration allows water, air, or moisture to get in creating rusting issues which could eventually cause the metal materials to be welded apart from each other. 


*Under-fill: Bad welds often are under-filled. A bad welder will use too much filler rod resulting in a messy and ugly-looking weld that doesn’t even cover the base plates of the metals being welded. Over-filling happens when an inexperienced welder uses too little filler rod which results in an excess amount of spatter coming out the welding point.


*Burn through: Bad welds tend to burn through both sides of the metals being welded. Bad welder tends to rush and push too much power resulting in an under-quality of the weld which is prone to leaking water, moisture, or air thru the welding point.

 Bad welds are also prone to blow-outs when the filler rod can’t handle too much heat and end up “popping out” from the point where you weld, making a big hole in your work or even worse bursting off!


*Whiskers: Bad welds tend to form tiny hairs or whiskers with time. Bad welds usually contain impurities that cause the whiskers to grow in time as you expose the weld to moisture and elements making it prone to rusting.


*Shiny Spots: Bad weld has shiny spots or patches probably caused by one of these reasons: a) The welder did not clean the metal parts prior to welding ) Bad welder uses low-quality filler rod which causes excessive spatter and therefore more patchy looking areas c) Bad filler rod used could have an excess amount of borax oxide, calcium oxide or magnesium oxide causing an unusual shine at places where they were used.


How to Recognize Good Weld vs Bad Weld? 

To be able to identify a bad weld from a good one, we will have to look at some obvious factors that all these methods have in common. These factors include appearance, fracture line, penetration, and fusion. Let’s discuss them.

– Appearance (Surface Finish)

Bad welds can easily be identified by their porous or rough appearance. For this reason, it is always advisable you get a certified product even from reputable manufacturers. 

Bad welds may be due to overheating while good welds are a combination of flat, smooth surfaces and rough spots. Bad welding can also result when there is too much heat produced during the process which causes porosity on the metal surface. 

Bad welds are often identified by small holes on its surface where oxygen or other gases escaped from the molten metal

The appearance of a good weld may also vary according to the welding process used and the thickness of metals being fused. For instance, the MIG method produces a clean edge on thin sheets of metal with little spatter but it is not as dominant for thicker material. On the other hand, the TIG method does not produce any spatter making them perfect for thick pieces of metal.


– Fracture line (penetration)

The fracture line of the good weld is smooth. Bad welds have a jagged surface which often causes cracks when subjected to pressure or heavyweight. Bad welds are easily identified after the metal cooled down because they leave puddle marks on its surface. 

 For instance, TIG welder produces little porosity during the process. Bad weld repairs can be done with proper training and welding equipment but if left unchecked can cause further damage to other parts of your car.

 It is also advisable that you get the work checked by a certified mechanic before using it in any way possible for safety measures.


– Fusion (penetration)

Good fusion is indicated by a complete absence of pores where one metal touches another. Bad fusion is where the metal shows a complete absence of penetration at its sides. Bad fusion is usually caused by the heat used in welding and can be identified when there are puddle marks on the surface of metal after it has cooled down.


– Uniformity of the surface

Good welds are smooth and flat with no pores. Bad weld has rough spots on its surface. Bad welding is caused by the use of non-consistent materials or heating temperatures that cause porosity on metal surfaces.

It is important that you know what your expectations are before choosing a welding inspection method because some methods may not work best for the type of material you’re using. 

Ultrasonic testing is applied to larger, complex parts where it’s hard to spot bad welds while X-ray machines and gamma-ray scanning can be used on smaller parts.

If your welding still doesn’t turn out as expected after using the methods above, then you may need to consider finding a better welder or hire a professional to help you with your work. 

Bad welds waste time, resources and money so make sure that they are left out of your final product.


12 Quality Testing Methods to Help you Know if a Weld is Good  

Visual spotting may not work. This is because some signs are beyond the eyes. You must do some deep tests to identify good vs bad welds. Here are some of the tests that you can do to conduct the test.

– Impact Test

Impact Test


You can also do an impact test on your welds by hitting your metal piece with a hammer. Bad welds produce brittle metals that break easily when hit while good ones are solid enough to require more force before breaking.

 This test is interesting because you need to hit the welds with a lot of force to make them perform poorly, but you won’t need as much force when testing for good welds.


 – Finger Press Test

This is basically just like the impact test except that it uses your finger instead of a hammer. Bad welds will produce brittle metal that breaks easily while good ones are solid enough not to break. 

However, it is not an ideal method for spotting bad weld and quality weld.


 – Tack Weld Test

Many people think that tack welds are useless since they do not hold metals together well but this is not entirely true. This is because tack welds are used to help in positioning things together and ensuring good alignment. 

Even if it doesn’t hold them together well, bad or off-centered tacks may affect how the pieces fit into each other causing damage later on when the project is complete and ready for use.


 – Gas Weld Test

This is a simple test that you can perform. With a welding torch, touch the part of the weld that you intend to test for gas content. The parts with gases will have some sparking and vapor release at your end while those without gases won’t give any reaction at all.


 – Mirco Slag Test

When an arc begins, some slag material forms on the metals surrounding the weld area and this should be avoided. Bad welds have excess slag while good welds don’t have any at all.

 You can use a sharp core bit or wire brush to remove the excess slag from both sides of the metal before proceeding with your welding procedure. 

The parts that are not removed in this step should show signs of good weld in terms of smooth surface and absence of misalignment. Also, observe whether there are bubbles inside them or not for further confirmation.


 – Backbend Test

This test is usually done for thin metal plates and sheeting. When bent, a good weld will return back to its original shape with no deformation or buckling but bad welds will retain the impact mark. This test will also help you to know if it is bent by hand or done with a machine.


 – Electromagnetic test (Eddy Current)

Electromagnetic test


Bad welds don’t conduct electricity just like the bad metals do so this method is suitable for both welded materials and parts as well as raw metals. 

Badly welded metal shows no signs of resistance while good ones have some level of resistance. Bad metals also produce misshapen electric waves that make it easy to identify with this method.


 – X-Ray Testing For Weld(Industrial Radiography)


X-Ray Testing


Weld X-ray machines can be used for spotting good bad welds and quality welds. Bad welds show clear signs just like they would when scanned using a gamma-ray machine. Bad welds are easily visible through the X-ray due to discolorations, misalignment, and other damages. 

Powerful X-ray machines are used for this method. This method of weld test and inspection is very accurate and is only recommended for professionals. It is also suitable for different shapes and sizes of metals.

 You can even use the method on irregularly shaped objects. You can also use it for testing the interior parts of the object.


 – Gamma Ray Testing(Industrial Radiography)


Gamma Ray Testing


This is sometimes used to detect bad welds since it can show internal flaws in the metal. Bad metals have some electron irregularities and these irregularities become more pronounced as you approach the core of a steel sheet. 

Badly welded parts are easy to spot because they give off abnormal radiations when scanned by this device while good ones don’t give any response or respond very slightly. 

This method is ideal for the complex parts where your eyes cannot tell the differences between bad and good welds since it provides clear pictures of these flaws. 

Gamma ray testing is only recommended for skilled professionals. Bad welds are bound to have some visible signs like burn marks, discoloration, and other damages but sometimes the experts fail to spot them because they can seem normal during a visual inspection, making this method one of the best methods out there. 


 – Ultrasonic Testing

  Ultrasonic testing


Bad welds produce brittle and misshapen metals that are easy to spot with this method since the sound waves that are produced during ultrasonic testing resonate well with a good metal but not at all with bad ones.

Bad welds also show signs of buzzing noises while good ones produce none making this method very effective in detecting bad welds. This method can be used on both welded parts and raw materials such as steel sheets, bars, or tubes.


 – Magnetic Particle Test

Magnetic Particle Test


Good metals are magnetic because they contain iron, cobalt, or nickel while bad ones are non-magnetic and often made from plastic or cast iron. Bad welds can be identified via simple tests such as using a magnet on the metal part or trying to grind it off by running an electrically powered grinding wheel over it. 

Bad welds won’t take long before crumbling to dust. Bad welds are also easy to spot during visual inspections due to burn marks, discoloration, and other damages.


– Penetrant Test

Penetrant Test


Bad welds are usually thinner than the good ones since they have a lower melting point meaning you can easily scrape them off after applying acids or alkalis on them then comparing. 

Bad metals can sometimes be detected by simply looking at how shiny they look because bad metals give off a dull look compared to the bright look of solid steel.


What are Common Causes that Lead to Bad Welding?    

Lack of fusion: When a weld has incomplete penetration, it is considered a poor or bad weld. When the entire cross-section of the joint does not have full fusion, then you have failed to make an acceptable weld. Lack of fusion is caused by many factors and among them is poor heating.


Irregular weld porosity: Irregular weld porosity is a bad or poor weld. The size and shape of the pores in the weld are irregular which prevents it from being used to carry the load. Irregular porosity can be caused by dirty or contaminated electrodes, overheating during welding, and lack of attention to certain details.


Faulty wire delivery: A weld with bad or poor wire delivery is always a defective weld. Wire delivery can be affected by several factors including the improper setting of the welding current, incorrect wire size, lack of operator attention to details such as number and thickness of passes, etc. Faulty wire delivery results in an inferior product that cannot be used for its intended purpose.


Improper weld bead profile: Improper weld bead profile is a bad or poor weld. Bead profile may look fine but if it does not conform to the standard design, then you have made an improper weld.

Improper bead profile can be caused by incorrect electrode size and shape which do not match the wire size being used in the welding process. For example, a 6013 electrode will create a different weld bead pattern than that of a 6010 electrode.


Incomplete weld penetration: Incomplete weld penetration is a bad or poor weld. The full cross-section of the joint should have complete fusion for the weld to pass as acceptable.

If there are areas within the entire thickness of the metal which do not have any fusion, then you have failed to make an acceptable weld.

 Incomplete penetration can be caused by poor heating or lack of attention to certain details like the number of passes and characteristics of the metal being welded.


What Causes Bad Welding?  

Bad or poor welds are caused by 1 of 3 reasons: Lack of Penetration / Long Weld Length, Excessive Heat Input(Overheated), or Inappropriate Voltage.

Contrary to popular belief, bad welds are NOT caused by dirty welding leads and electrodes. Although, cleaning them before use helps limit contamination later on in the process.

Although other causes may contribute such as poor technique from the operator (not enough arc time) and lack of fit-up due to either equipment design issues or improper fixture set-ups.


Can you Weld over a Bad Weld?  

Technically – yes. But there are lots of factors that you will have to consider when repairing a bad weld. One of them is the cause of the bad weld.

However, I don’t recommend it because most bad welds are created from excessive heat & impurities such as oxides present in the base metal and/or contributing material.

Therefore, by welding over a contaminated surface – you’re just trapping any existing impurities within the molten pool of filler metal and creating a brand new bad weld.

But, if you’re going to try anyway – I suggest that you be extra vigilant with every step that you take when repairing a bad weld.


Best X-Ray Machine for Welding Inspection  

At UNI X-ray, we have advanced X-ray machines(UNC180) that you can use for spotting quality welds and bad welds. So, if you are heavily involved in the welding industry, our machines will prove useful.

Our X-ray machines have advanced features that will enable you to find out the difference between good and bad welds. 



Well, there you have it! These are the different types of welds that can be used in manufacturing metallic products. From here, you will be able to tell a good weld from a bad one.

It should be noted that these tips in identifying good and bad welds do not apply to all types of metals but can be used as a general guide to help you determine what you might want to look for when inspecting your car before using it.

There are many ways through which substandard products enter the marketplace. Badly done major repairs may cost several thousands of dollars in rectification works. 

To avoid this from happening, always get your work checked by a certified mechanic after every major work done so you know exactly what is good, what’s bad, and whether it is fit for use.



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