10 Things to Consider When Buying Ut Thickness Gauge

Does it often feel frustrating when choosing a suitable ultrasonic thickness gauge to meet your inspection requirements?

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Understanding your inspection requirements is one thing but choosing the suitable ultrasonic thickness gauges is a whole different ball game. It often requires a completely different set of skills from determining quality assessment requirements. However, choosing the best suited ultrasonic thickness gage is not impossible. All it requires is following a set of carefully mapped out plans and considering critical factors that can make your decision process easier.

This post will show you all the requirements and essential factors you should consider when purchasing an ultrasonic thickness gauge. 

So, if you&#;re ready, let&#;s dive into it. 

 

 

Ultrasonic Thickness Gauge Explained

Like all non-destructive testing tools, ultrasonic thickness gauge is a device that ensures the test sample is intact after the test. However, its primary function is to measure the thickness of materials against a specified standard thickness. Invariably, material thickness changes over time due to the effects of such things as corrosion or erosion. And so, most technicians try to ascertain the level of change in this thickness using this device. 

Other thickness-measuring devices like a caliper or a micrometer gauge usually measure thickness from two sides. On the other hand, an ultrasonic thickness gauge measures thickness with access to one side only. Yet, it has proven faster, more versatile, and more reliable than most non-destructive thickness measuring devices. 

Primarily, it works using the laws of ultrasonic sound wave projection. It uses standard waveforms for sound traveling in a medium like steel or other materials to compare the generated waveform for the test sample. 

 

Types of Ultrasonic Thickness Gauge

While the application of ultrasonic thickness gauges is common for ascertaining the level of corrosion damage to metal structures like pipes, tanks, and tubes, the gauges employed come in one of two types, corrosion gauges and precision gauges. 

Naturally, the choice of which ultrasonic thickness gauge you make will be influenced by the test material and the number of transducer elements required to achieve the inspection. 

• Corrosion Gauges

  &#; With a combination of signal processing and internal detection techniques, corrosion gauges are very effective for measuring the level of internal corrosion in metal structures like pipes and vessels. This measuring effectiveness stems from the ability of the ultrasonic thickness gauge to measure the thickness with access to just one side of the test sample. One other thing is that corrosion gauges use dual element transducers to achieve thickness measurements. 

• Precision Gauges

  &#; For other materials like fiberglass, rubber, ceramic, and plastics, precision gauges are more effective. Though they use a single element transducer, they can identify the reduction in thickness of the material walls with access to just one side of the material. 

 

Choices of Transducer Types for Ultrasonic Thickness Gauge

Generally, the transducer types available for ultrasonic thickness include contact transducers, delay line transducers, immersion transducers, and dual element transducers. The choice of transducer that you choose will depend on the level of accuracy you desire for a given thickness measurement.

• Contact transducers

  : By far the simplest to implement, contact transducers often contact the test sample when carrying out the thickness measurement. And, because of its simplicity, it has become the most preferred choice for most technicians.

• Delay Line transducers

  : Delay line transducers are often the most effective for measuring very thin materials. The reason lies in their ability to interrupt external pulse excitation from back wall echoes using a cylinder known as a delay line. This disruption is necessary so the echoes don&#;t interfere with the main pulse coming from the test material to the receiving element. The delay line is often made from epoxy, silica, or plastic material. Also, hot test samples act as a protection for the temperature-sensitive transducer element. 

• Immersion transducers

  : This transducer is often very effective for applications involving moving parts or in-process measurements. It employs a water column to transmit sound waves into the test material. Apart from in-process measurements, immersion transducers also choose materials with channels or grooves. 

• Dual element transducers

  : Often employed for rough corroded surfaces, dual-element transducers are very effective. These transducers are only used with corrosion gauges. 

 

 

How to Select the Right Ultrasonic Thickness Gauge?

Choosing a suitable ultrasonic thickness gauge requires considering certain critical factors to make your decision-making process smoother. Here is a list of essentials you should consider in your quest to choose the right ultrasonic thickness gauge.

• Material

   &#; This factor is by far the most important one on this list, and the reason is this. Materials absorb or transmit ultrasound differently. For example, certain materials, including glass, metals, and ceramic, transmit ultrasound effectively with materials like rubber absorbing ultrasound. Hence, choosing a reliable ultrasonic thickness gauge will require that you understand the reaction of the test material to ultrasonic waves. 

• Thickness

  &#; The thickness range specified during measurement is also as important as the material type. The reason is that the thickness range determines the thickness gauge required to achieve a satisfactory result. It is also important for the accuracy anticipated for the thickness measurement. For instance, you might use a delay line transducer to get a highly accurate measurement for thin materials. However, thicker material may require contact or dual-element transducers to measure accurately. The high frequency required for thin materials and low frequencies for thick materials also largely determine the required thickness gauge type. 

• Surface

  &#; The smoothness or roughness of a material surface is highly important in choosing a thickness gauge suitable for a thickness measuring inspection. Generally, ultrasonic thickness gauge with a dual-element transducer is effective for rough surfaces. In contrast, other transducers are generally suitable for other forms of thickness measurements. 

• Geometry

  &#; The ease of coupling the test material and the transducer significantly reduces. Hence, considering the geometry will help you choose the suitable transducer that will give an accurate reading based on the level of irregularity or the radius of curvature of certain parts of the test sample. Curvature naturally limits the choice of a transducer to either delay line transducer or the immersion transducer. Additionally, materials with channels and grooves are also often measured with immersion and delay line transducers. 

• Temperature

  &#; The sensitivity of transducers for most ultrasonic thickness gauges varies significantly as temperature increases. It is generally adequate for primary contact transducers to be accurate within a temperature range of up to 50 degrees Celsius. Once the temperature exceeds this range, only special transducers will be suitable for these measurements as the delicate elements within the transducers will be permanently destroyed. These special transducers may include immersion, delay line transducers with heat resistance, and dual element transducers. These special transducers will help you achieve an accurate thickness measurement in this case. 

• Phase Reversal

  &#; The bonding between materials of different acoustic impedances in special cases like the insulation of metals with rubbers or plastic bushings on metal pipes significantly affects your choice of a suitable ultrasonic thickness gauge. The acoustic impedance is calculated by multiplying the velocity of the sound with the density of the material and can greatly influence the accuracy of the thickness measurement if the right thickness gauge is missing. The echoes at the boundary of the connection between the materials often introduce a phase reversal with inaccuracies for the thickness measurement. Nonetheless, a simple setting before the device setup can adequately accommodate this irregularity to deliver an accurate result. 

• Measurement Range

  &#; The range of thickness measurements anticipated is also important. You don&#;t choose an ultrasonic thickness gauge that is far above the actual measurement range or one that is far below it. Choosing a thickness measuring device without adequate consideration for measurement range can have significant cost consequences. 

• Accuracy

  &#; This factor forms the basis for all quality assessments as technicians and quality assurance officers ensure the accuracy of measuring devices using tools like calibration. Consequently, you need to consider the level of accuracy required for the specific thickness measurement to choose the suitable ultrasonic thickness gauge. As such, technicians utilize other tools along with device calibration, including material sound velocity, sound scattering, attenuation, and sound couplings to ensure the high accuracy of the measuring device. Also, the process of calibration should follow standard practice using acceptable reference standards and known thickness. Hence, measurements that require an accuracy of 0.01mm will require a different ultrasonic thickness gauge and transducer than if the accuracy requirements were 0.001mm. Nevertheless, immersion and delay line transducers are adequate for generally high accuracy requirements.  

• Operation

  &#; Given certain conditions, your choice will greatly affect how easy it is to operate an ultrasonic thickness gauge. For instance, where there is limited access to the test sample, some thickness gauges might be more suitable than others. Identifying these constraints gives you an idea of the best thickness gauge for that operation. 

  Contact us to discuss your requirements of Ut Thickness Gauge. Our experienced sales team can help you identify the options that best suit your needs.

  Suggested reading:
  Is Film Heat Seal Testing Really Necessary?

• Durability
  Portable Ultrasonic Flaw Detector vs Traditional Inspection Methods: Which is More Efficient?

   &#; What applies to highly durable and sturdy test samples will differ considerably from a fragile test sample. Careful consideration of this factor will allow you to choose the best ultrasonic thickness gauge without destroying the sample object. 

 

Knowing how to choose your right ultrasonic thickness gauge, I bet you also want to know where you can find the best thickness gauge manufacturers, and which one is the best. Here&#;s the top 10 ultrasonic thickness gauge manufacturers guide for you.  

Also, click to continue to read how to use ultrasonic thickness gauge, if you are interested in.

 

 

Conclusion

To wrap up, choosing the right ultrasonic thickness gauge for your thickness inspection operation is essential and possible if adequate consideration is given to critical factors that can adversely affect the result of the thickness measurement. While these factors include material thickness, measurement range, accuracy required, ease of operation, and durability, it is equally important to know the type of transducers available for thickness measurement operations. 

Ultimately, following the information given in this post will ensure that you choose the best suited ultrasonic thickness gauge for your exceptional thickness measuring needs with consistently accurate results every time.

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When it comes time to choose the proper ultrasonic thickness gage for your needs, many factors must be considered. Many of the important points are obvious such as budget and your basic application. Other factors may not be, and careful consideration should be given to them so that you are happy with your short and long term selection from a vast group of quality manufacturers of these simple yet high technology devices. 

Here are some things to consider when selecting your next ultrasonic thickness gage. Obviously, budget is always something to be conscious of. Handheld ultrasonic thickness gages, depending on the vendor and where they are made, can range from just a few hundred dollars to more than $4,000. There are also many factors involving the application. It is important to know beforehand what the instrument can and cannot do so that you and the supplier do not have a misconception of the instrument&#;s capabilities. 

It is critical to list the materials and complete thickness range of each material along with desired accuracy, temperature at the time of the readings, surface finish (painted), if the surfaces are parallel, and if a fluid can be applied to the material. The fluid is usually a water soluble ultrasonic couplant required for high frequency sound to enter the part as the ultrasonic frequencies are in the millions of cycles per second and do not travel through air. 

Other factors are more related to individual preferences and options such as the need to use echo to echo to ignore coatings and live waveform referred to as A-scan (more details below), an internal datalogger, temperature correction, oxide scale, high penetrations, use of different frequencies, diameters and types of probes such as a pencil probe vs. a dual probe. Other considerations should be given to the environment in which the product is used such as indoor vs. outdoor use for both IP rating for dust and moisture and display type and size for viewability including in direct sunlight. 

You should also consider weight, size and battery type. Some units are very small and can fit in your shirt pocket and utilize the convenience of AA type alkaline batteries while others offer more than 24 hour battery life utilizing the latest in lithium Ion rechargeable batteries at the sacrifice of a larger unit. Also, careful consideration should be given to serviceability of the unit, where it is manufactured and the reputation of the vendor&#;s customer service and track record. 

In addition to budget, here is a list of things to consider for these applications: 

• Material or materials to be measured. Essentially any engineering material can be measured within a specific range. It is important to list all materials and the thin and thickness range to be measured.
• Thickness range of each material
• Are the front and back surfaces parallel
• Surface condition, smooth, painted rough (RMS finish)
• Temperature at time of reading. Sound velocities can change during a curing process such as a piece of plastic out of a blow molding machine. This would not be a good application. 

Also, consider these questions: 

• Can a fluid be applied to the material referred to as ultrasonic couplant? As with medical ultrasound when imaging babies, ultrasound does not pass through air and a fluid needs to be applied to the material for ultrasound to enter the part. 
• Do you have direct access to the part?  A buried pipe is not a good application as you must have direct access to the part by touching it or spraying water on it (immersion technique)
• Desired accuracy, such at .01&#;, .001&#;, .&#; (.1, .01, .001mm)
• Is the part painted? See below for more details on this application. 
• Do you require datalogging, save and send readings to the computer for permanent documentation? An example would be studying corrosion rates in a pipe or storage tank.
• Do you need to view the live waveform (A-scan), see below regarding why this is important
• Do you want to consider a unit with an upgrade path (field upgradability to unlock software options and no need to return the instrument to the factory)?

In addition, consider the physical size of the unit (fits in shirt pocket vs. handheld); environmental concerns such as IP rating or explosion proof; display size; display color or monochrome; sunlight readability; and reputation of vendor.

Ultrasonic Thickness Gages

Ultrasonic testing and the use of thickness gages using ultrasound is a very well-known technique. The primary reason for using an ultrasonic thickness gage is you can nondestructively test the wall thickness of the material without destroying the part. Commonly the two primary uses are for detection of wall thinning due to corrosion or as a quality control tool for material thickness consistency. The applications range from measuring pipes, tubes, boilers, ship hulls-considered corrosion to plastic bottles, toys, coil steel, aircraft aluminum and coil steel-considered precision, to name a few. 

There are many manufacturers of such products around the world. Handheld units can start as low as a few hundred dollars and can go up to several thousand dollars. Obviously, there will be a distinct tradeoff from the price you pay to the feature set that is included. Nowadays, software is very flexible and many manufacturers use the same basic electronics to satisfy budget and application needs but vary the internal software to satisfy more challenging needs. Several companies now offer the convenience to do field upgradability. What this means is a basic instrument of &#;thickness only&#; can unlock software to enable features such as echo to echo, datalogger and live waveform. This is a tremendous convenience and saves time and money as there is no downtime or extra shipping costs. 

One common example of this is a technique referred to as echo to echo. Here is the basic application and solution. Many times parts such as a storage tank or steel ship hull are painted. When using an ultrasonic thickness gage without the echo to echo feature, the thickness of the paint will introduce an error of roughly 2.5 times the thickness of the paint. The reason for this is the sound speed used to measure the base steel is 2.5 times faster than paint. So a .010&#; (.25mm) thickness of paint will introduce a .025&#; or .625mm error. The echo to echo technique offered by many manufacturers measures the time between two successive backwall echoes in the base material thus taking the paint thickness out of the equation. 

Some consideration should be given to the thickness of the base material as most vendors will state the base material should be at least .100&#; or 2.5mm in echo to echo mode. Also consider a more heavily damped transducer and ideally viewing the live waveform to verify the echoes are legitimate is recommended. Using a &#;thickness only&#; gage with just numbers and not a live waveform, particularly on thin materials can miss a doubling effect. This could show a reading of .120&#; when in fact the part is one half that or .060&#;. By viewing the live waveform, a trained operator could see this error. 

I like to compare this to fishing. On a boat you can have a depth finder. This would be equivalent to a gage with a &#;thickness only&#; display while a &#;fish finder&#; would be equal to a thickness gage with a live waveform. While a boater could determine if the changing depth of the water was just the water, it could be a rock, a whale or bait, the same is true of the thickness meter with the live waveform where an operator can look for things such as doubling, mode converted echo errors or even flaws and delamination if large enough. Some vendors call this top coat or through coat. In these cases, some companies have patents on their respective techniques. 

Modern ultrasonic thickness gages have internal dataloggers, some with up to 32 GB of micro SD card memory. Other unique features include blue tooth and direct interface to Microsoft Excel. Readings can be given file names, user names, locations, prefix, notes and set up in files such as linear, 2D, 3D, boiler and with custom points. This allows for a great deal of flexibility when collecting and comparing readings over inspection outages.

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