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Steel surfaces are frequently cleaned by abrasive impact prior to the application of protective coatings. This process removes previous coatings and roughens the surface to improve coating adhesion. The resultant surface profile is comprised of a complex pattern of peaks and valleys which must be accurately measured to ensure long-term coating performance.
A surface profile height that is too low may reduce coating adhesion and corrosion resistance. Too high and the peaks may receive insufficient coverage leading to premature rusting, and requiring additional paint to cover the anchor profile.
The PosiTector SPG Surface Profile Gage is popular for users who want a fully-digital test with zero per-test cost. The digital depth micrometer is fitted with a fine-pointed probe to measure and record peak-to-valley surface profile heights in accordance with ASTM D method B and SSPC PA 17. During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys.
A fast measurement rate of over 50 readings per minute makes it ideal for quickly measuring surface profile over large areas. All probes feature a durable alumina wear face and field replaceable tungsten carbide probe tips for long life and continuous accuracy. PosiTector SPG probes connect to the interchangeable PosiTector Platform, quickly transforming from a surface profile gage to a coating thickness gage, dew point meter, gloss meter, and more.
DeFelskos other solution for measuring surface profile, the PosiTector RTR Replica Tape Reader, uses industry-standard Textex Tape to measure profile height. Models are also available that can create 3D images from the replica tape to measure peak count and other surface profile parameters. Learn more about the PosiTector RTR in the How to Use Replica Tape to Measure Surface Profile video at the Link in the description below.
The PosiTector SPG is available as an integral model for one-handed operation or a cabled model for improved ergonomics in hard to reach areas. The PosiTector SPG OS model features a V-groove and proprietary OD mode for measuring convex surfaces with outside diameters greater than 3 millimeters or an eighth of an inch, such as on pipes and tanks.
Additional models are available with a greater range and rounder tip for measuring the profile of textured coatings, the PosiTector SPG CS, and for measuring the profile of concrete, the PosiTector SPG TS.
Measuring surface profile with the PosiTector SPG is easy. First, verify that the instrument is operating correctly by placing the included shim on top of the glass zero plate. Place the tip of the probe on the glass while the base rests on both sides of the shim. Ensure the reading on the instrument is within the combined tolerance of the shim and the gage.
During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys. Ensure that the surface is free of dust and other contaminants, then place the probe foot level on the surface to be measured. The profile height is displayed on the gage.
ASTM D recommends taking ten readings at each location and recording only the maximum value, discarding any unusually high readings that cannot be repeated in an area. Average the maximum values at multiple locations and report it as the profile height. SSPC-PA17 recommends averaging the maximum values at a minimum of three locations to determine the profile height.
On competitive instruments, this method is challenging to follow and requires writing down many readings. PosiTector SPG Advanced models feature SmartBatch, making this process easy by automatically keeping only the highest reading in each spot, and averaging several spots together right on the gage.
Once measurement is complete, connect to the included PosiSoft Desktop software using a USB cable or WiFi to archive and manage measurements. Professional, custom reports can instantly be generated, including multi-batch reports
Depth micrometers such as the PosiTector SPG have no per-test cost and are a quick, reliable way of determining surface profile. Learn about all of the features and benefits of measuring surface profile with the PosiTector SPG at defelsko.com/spg.
Surface profile should not be confused with roughness. Surface profile is a measurement of the peak-to-valley height. Surface roughness, on the other hand, is the combined measurements of the surface profile and the frequency of the peaks across a linear length (also known as the peak count). Surface roughness is measured using a stylus instrument.
Now that we have defined surface profile as the peak-to-valley height, why is it important for the coatings industry to measure it?
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Quite simply, to avoid corrosion. Corrosion is typically caused when three things come together a ferrous material (in our case the steel substrate although it is worth noting that non-ferrous materials can also corrode), oxygen (from the air) and moisture. If you can remove just one of the 3 elements, corrosion (or more precisely aerobic corrosion) simply cannot happen. Applying a coating to the steel provides a barrier between the steel and both the air and moisture, preventing corrosion. So if the coating is damaged, or simply rolls off the surface due to poor adhesion, then the steel will rust, corrode, and in time weaken the structure. Not exactly ideal if you are coating a bridge for example.
Typically the surface profile specified is the peak-to-valley height in either microns or mils. The coating is also specified in either microns or mils, as a dry film thickness. The key here is that the required coating thickness is applied to both the valleys and the peaks, otherwise you get rust spots.
So, if the profile is too high, the amount of paint used to cover the peaks is significantly more, otherwise there are thin areas of cover resulting in poor protective properties, leading to rust rash and early failure.
If the profile is too low, then the coating applied can be too thick, leading to possible cracking of the coating whilst it dries (or cures), resulting in corrosion and pinholes. Not to mention that there may also be an insufficient surface area to provide a suitable key for the coating - leading to poor adhesion and premature coating failures.
So how do we measure surface profile?
There are a number of methods for measuring surface profile, and they all work in different ways.
Surface Comparators are flat, metal plates, which contain a number of reference surface profiles. The comparator is placed on the surface, which is compared with the reference profiles through either sight or touch. The profile is then determined and recorded. While this is a quick assessment of the surface profile, its a highly subjective method of measurement, as it can come down to the opinion of one person over another.
A widely used, and less subjective alternative is the Replica Tape method.
A tape with a compressible foam pad is applied to the surface, and rubbed with a burnishing tool. By rubbing the tape into the surface, the foam is pushed down, creating an inverse or mirror image of the profile. The tape is then removed and measured using a thickness gauge, such as the Elcometer 124 gauge. The replica tape method provides a peak-to-valley height measurement of the profile.
Unfortunately this method has a low stated accuracy, and the test itself is quite time consuming especially for some profile ranges where you need to test the same area with multiple grades of tape and take the average.
A faster, more accurate, and repeatable method for measuring surface profile is the new Elcometer 224 Digital Surface Profile Gauge.
The Elcometer 224 is a needle depth gauge, which is very easy to use. Simply zero the gauge on glass, and, when the gauge is placed on the surface, a spring mounted needle measures the depth of the profile from the peaks of the profile at that particular point. As the measurement point is not necessarily at the very bottom of the valley, and could be somewhere on the slope so to speak, the user takes either 5 or 10 individual measurements, after which the gauge then provides a reading.
The reading displayed is user selectable, and can either be the more common average peak-to-valley height, or the maximum height.
With the ability to measure profiles up to 500 microns (20mils), on flat or curved surfaces, the Elcometer 224 Digital Surface Profile Gauge provides repeatable and reproducible measurements [accurate to ±5%]; can store each reading into memory [150,000 readings in 2,500 batches] and can instantly transfer them to your PC or mobile device using ElcoMaster; our free, easy-to-use software application, generating professional inspection reports, instantly.
Whats more, the new Elcometer 224s measurement modes, make sure that you can collect and record the data you need in accordance with your relevant test method, or standard.
Click here to download the script in English
Products referenced in this video:
Steel surfaces are frequently cleaned by abrasive impact prior to the application of protective coatings. This process removes previous coatings and roughens the surface to improve coating adhesion. The resultant surface profile is comprised of a complex pattern of peaks and valleys which must be accurately measured to ensure long-term coating performance.
A surface profile height that is too low may reduce coating adhesion and corrosion resistance. Too high and the peaks may receive insufficient coverage leading to premature rusting, and requiring additional paint to cover the anchor profile.
The PosiTector SPG Surface Profile Gage is popular for users who want a fully-digital test with zero per-test cost. The digital depth micrometer is fitted with a fine-pointed probe to measure and record peak-to-valley surface profile heights in accordance with ASTM D method B and SSPC PA 17. During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys.
A fast measurement rate of over 50 readings per minute makes it ideal for quickly measuring surface profile over large areas. All probes feature a durable alumina wear face and field replaceable tungsten carbide probe tips for long life and continuous accuracy. PosiTector SPG probes connect to the interchangeable PosiTector Platform, quickly transforming from a surface profile gage to a coating thickness gage, dew point meter, gloss meter, and more.
DeFelskos other solution for measuring surface profile, the PosiTector RTR Replica Tape Reader, uses industry-standard Textex Tape to measure profile height. Models are also available that can create 3D images from the replica tape to measure peak count and other surface profile parameters. Learn more about the PosiTector RTR in the How to Use Replica Tape to Measure Surface Profile video at the Link in the description below.
The PosiTector SPG is available as an integral model for one-handed operation or a cabled model for improved ergonomics in hard to reach areas. The PosiTector SPG OS model features a V-groove and proprietary OD mode for measuring convex surfaces with outside diameters greater than 3 millimeters or an eighth of an inch, such as on pipes and tanks.
Additional models are available with a greater range and rounder tip for measuring the profile of textured coatings, the PosiTector SPG CS, and for measuring the profile of concrete, the PosiTector SPG TS.
Measuring surface profile with the PosiTector SPG is easy. First, verify that the instrument is operating correctly by placing the included shim on top of the glass zero plate. Place the tip of the probe on the glass while the base rests on both sides of the shim. Ensure the reading on the instrument is within the combined tolerance of the shim and the gage.
During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys. Ensure that the surface is free of dust and other contaminants, then place the probe foot level on the surface to be measured. The profile height is displayed on the gage.
ASTM D recommends taking ten readings at each location and recording only the maximum value, discarding any unusually high readings that cannot be repeated in an area. Average the maximum values at multiple locations and report it as the profile height. SSPC-PA17 recommends averaging the maximum values at a minimum of three locations to determine the profile height.
On competitive instruments, this method is challenging to follow and requires writing down many readings. PosiTector SPG Advanced models feature SmartBatch, making this process easy by automatically keeping only the highest reading in each spot, and averaging several spots together right on the gage.
Once measurement is complete, connect to the included PosiSoft Desktop software using a USB cable or WiFi to archive and manage measurements. Professional, custom reports can instantly be generated, including multi-batch reports
Depth micrometers such as the PosiTector SPG have no per-test cost and are a quick, reliable way of determining surface profile. Learn about all of the features and benefits of measuring surface profile with the PosiTector SPG at defelsko.com/spg.
Surface profile should not be confused with roughness. Surface profile is a measurement of the peak-to-valley height. Surface roughness, on the other hand, is the combined measurements of the surface profile and the frequency of the peaks across a linear length (also known as the peak count). Surface roughness is measured using a stylus instrument.
Now that we have defined surface profile as the peak-to-valley height, why is it important for the coatings industry to measure it?
Quite simply, to avoid corrosion. Corrosion is typically caused when three things come together a ferrous material (in our case the steel substrate although it is worth noting that non-ferrous materials can also corrode), oxygen (from the air) and moisture. If you can remove just one of the 3 elements, corrosion (or more precisely aerobic corrosion) simply cannot happen. Applying a coating to the steel provides a barrier between the steel and both the air and moisture, preventing corrosion. So if the coating is damaged, or simply rolls off the surface due to poor adhesion, then the steel will rust, corrode, and in time weaken the structure. Not exactly ideal if you are coating a bridge for example.
Typically the surface profile specified is the peak-to-valley height in either microns or mils. The coating is also specified in either microns or mils, as a dry film thickness. The key here is that the required coating thickness is applied to both the valleys and the peaks, otherwise you get rust spots.
So, if the profile is too high, the amount of paint used to cover the peaks is significantly more, otherwise there are thin areas of cover resulting in poor protective properties, leading to rust rash and early failure.
If the profile is too low, then the coating applied can be too thick, leading to possible cracking of the coating whilst it dries (or cures), resulting in corrosion and pinholes. Not to mention that there may also be an insufficient surface area to provide a suitable key for the coating - leading to poor adhesion and premature coating failures.
So how do we measure surface profile?
There are a number of methods for measuring surface profile, and they all work in different ways.
Surface Comparators are flat, metal plates, which contain a number of reference surface profiles. The comparator is placed on the surface, which is compared with the reference profiles through either sight or touch. The profile is then determined and recorded. While this is a quick assessment of the surface profile, its a highly subjective method of measurement, as it can come down to the opinion of one person over another.
A widely used, and less subjective alternative is the Replica Tape method.
A tape with a compressible foam pad is applied to the surface, and rubbed with a burnishing tool. By rubbing the tape into the surface, the foam is pushed down, creating an inverse or mirror image of the profile. The tape is then removed and measured using a thickness gauge, such as the Elcometer 124 gauge. The replica tape method provides a peak-to-valley height measurement of the profile.
Unfortunately this method has a low stated accuracy, and the test itself is quite time consuming especially for some profile ranges where you need to test the same area with multiple grades of tape and take the average.
A faster, more accurate, and repeatable method for measuring surface profile is the new Elcometer 224 Digital Surface Profile Gauge.
The Elcometer 224 is a needle depth gauge, which is very easy to use. Simply zero the gauge on glass, and, when the gauge is placed on the surface, a spring mounted needle measures the depth of the profile from the peaks of the profile at that particular point. As the measurement point is not necessarily at the very bottom of the valley, and could be somewhere on the slope so to speak, the user takes either 5 or 10 individual measurements, after which the gauge then provides a reading.
The reading displayed is user selectable, and can either be the more common average peak-to-valley height, or the maximum height.
With the ability to measure profiles up to 500 microns (20mils), on flat or curved surfaces, the Elcometer 224 Digital Surface Profile Gauge provides repeatable and reproducible measurements [accurate to ±5%]; can store each reading into memory [150,000 readings in 2,500 batches] and can instantly transfer them to your PC or mobile device using ElcoMaster; our free, easy-to-use software application, generating professional inspection reports, instantly.
Whats more, the new Elcometer 224s measurement modes, make sure that you can collect and record the data you need in accordance with your relevant test method, or standard.
Click here to download the script in English