Weld Quality Testing: Visual, Physical & NDT

Weld Quality Testing

In order to evaluate the quality of welds, to be accepted as meeting a tolerance level for a welded structure, it must be assessed by adequate testing methods. Hence the structures will undergo a proof test under the same or worse conditions than that for welded structures.

This page has tips on visual inspection. The following pages has inspection techniques for GMAW and physical weld testing.

These tests expose weak or defective areas that can be addressed prior to releasing the material to operational use. The tests also determine the suitable welding design for ordnance equipment and prevent injury and inconvenience to personnel.

NDT is short for nondestructive testing. It is a way of testing and it is based on checking the weld without damaging it. It is a time and money saver consisting of remote visual inspections (RVI), x-rays, ultrasonic testing and liquid penetration testing.

For most welds, we are testing the quality based on the intended function of the weld. If you are repairing a part on a machine, and the machine works as it should, we often accept the weld as ‘correct’. There are a few ways to indicate if a weld is ‘correct’:

• Distribution: The weld material should show an equal distribution across the two materials being joined.
• Waste: There should be no waste in the weld, such as slag that should peel off the project upon cooling and be easily removed. In MIG welding, any residual shielding gas will also be able to be easily removed. Since TIG is the cleanest welding process, there should be no waste. If there is waste in TIG welding and you have followed proper cleaning practices, it is most likely due to waste in the material being welded.
• Porosity: The weld surface should be smooth and free from irregularities or porosity (porous holes). Holes add weakness to the weld. If you have holes, it often signifies that the base metal was too dirty or had some form of an oxide coating. In MIG or TIG welding, porosity signifies the need for more shielding gas while welding. Porosity of aluminum welds can be a key indication that you are not supplying enough gas.
• Tightness: If the joint is not tight, this indicates some form of a welding issue. In oxyacetylene welding if using autogenous welding (no filler) the weld must be tight. If using TIG autogenous welding the same applies. In the case of other kinds of welds (when filler is used), any gap will be filled with the filler. However, anytime there are gaps, there is an indication there may be a quality issue.
• Leak-Proof: If you are repairing a product that has liquid in it, a leak is an easy (and obvious) way to establish there is a problem. The same is true with something that houses gas. One method to test for leaks, if possible, is to put soap bubbles on it – this can even be done with a squirt bottle!
• Strength: Most welds will require a certain strength. What you can do to ensure you get the strength required, is to start with a filler and electrode rating higher than what your strength requirement is.

Additional checks that can be made by sight include checking before (the root face, the gap, bevel angle, joint fit), while (the rate of electrode consumption, metal flow, arc sound and light) and after welding (undercut, root fusion problem, pin holes, excess spatter, weld dimensions).

Visual Inspection (VT)

Visual inspection is a non-destructive testing (NDT) method of assessing weld quality in which a weld is examined with the naked eye for surface defects. It is the most common method of weld testing.

Advantages of nondestructive weld quality testing:

• Inexpensive (usually only labor expense)
• Low-cost equipment
• No power requirement
• Quick identification of defects and downstream repair costs due to issues that weren’t caught early

Disadvantages:

• Inspector training necessary
• Good eyesight required or eyesight corrected to 20/40
• Can miss internal defects
• Report must be recorded by inspector
• Open to human error

Visual Weld Quality Testing Steps

Practice and develop procedures for consistent application of the approach

1. Inspect materials before welding
2. Weld quality testing when welding
3. Inspection when weld is complete
4. Mark problems and repair the weld

Visual Inspection During Welding

• Verify electrodes for correct size, type, and storage (Low hydrogen electrodes are maintained in a stabilizing oven)
• Watch root pass for chances of cracking
• Review each weld pass. Look for undercut and required contour. Verify weld was cleaned properly between each pass.
• Look for craters that need to be filled
• Check weld sequence and size. Gauges are used to check size.

Inspection After Welding

• Check weld against code and standards
• Check size with gauges and prints
• Check finish and contour
• Check for cracks against standards
• Look for overlap
• Check undercut
• Determine if spatter is at acceptable levels

How to know if it’s a Weld Discontinuity or a Welding Defect

A weld discontinuity is easily recognized because it is an interruption in the continuous flow. It can also be called a weld imperfection, and it can be found either in the weld metal or in the parent metal.

A discontinuity occurs in the weld metal due to the incorrect welding pattern and hydrogen cracking or stress. This can take on a variation from the original weld bead shape, thickness, and ultimately the quality.

Generally speaking, you want to avoid a discontinuity and make adjustments, but they are slightly less critical than a welding defect. Either way, if you have a weld discontinuity, you need to take care of it.

That said, an accumulation of weld discontinuities, can eventually become a weld defect, if they exceed allowed limits, according to your job. This is determined according to your country, the material types and type of environment you are working in.

In conclusion, the best way to inspect any welding job, especially in tight spaces, is to use a welding camera. Here are some video examples of how that works.

Identifying Welding Defects Before It’s Too Late

To say that identifying welding defects in a timely manner is vital would be an understatement. Even the smallest defect can be disastrous.

Welding is a complicated technique or craft that requires attention to detail. From the direct application of the welding technique to the welding current, supervision, etc., the craft of welding is complicated and requires sensory perception and awareness of its complexities.

A company that makes investments in the proper tools will be able to carry out the work easily, safely, and expediently.

Ultimately, it is very important for companies in the oil, gas, and mining industries to know what to look for when identifying some of the most commonly occurring welding defects, so that they can act.

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