Ground Penetrating Radar: Utility Mapping


One of the major uses of Ground Penetrating Radar is to locate most utility lines, big or small. This is not only to find them in case of repairs, but also for construction site digs so that they are mapped out and easily avoided to avoid unnecessary damage which, in turn, avoids unnecessary costs.

  • Utilities GPR Can Locate

  1. Communications and Data Lines – Whether in a residential or commercial setting, it is highly recommended that these utilities are located to prevent unnecessary downtime and unnecessary costs. Communication and Data lines include, but are not limited to, phone lines, high speed internet lines, cable television lines, and the like.
  2. Gas, Water, and Sanitary Lines – Even more important than communication and data lines, all sorts of gas, water, and sanitary lines are able to be located with the correct equipment. Successful mapping of these lines will ensure that digs can be made in the correct areas to make necessary repairs, or so that these lines can be avoided altogether to avoid damage. As you know, if one of these lines is hit during a dig, thousands of dollars in repairs could be the result.
  • GPS Mapping of Utilities Located

  1. Once said utilities are located underground using GPR equipment, a GPS unit is able to be attached to the unit itself. Using the most groundbreaking software, it is possible to map out the utilities. Once these utilities are mapped out, not only can specific coordinates be provided, but a mapping system compatible with Google maps is also possible.

The Basics of Non Destructive Testing – Part 1

Ultrasonic testing of a pipeline weld

Non-destructive testing methods test mechanical and other properties without permanently altering the subject, which saves time and money in product evaluation.

There are many companies that sell non-destructive machines to test material properties but they rarely explain how their methods work. Eng-Tips Forums member “afronova” posted the question, “Are there any good sites that inform about destructive and non-destructive material testing techniques?”

Well, afronova, there is now.

And so begins a three-part series on nine methods of non-destructive material testing. In part one, we discuss radiographic testing, ultrasonic testing and magnetic particle inspection.

1. RT – Radiographic Testing

Radiographic testing is often used to inspect assembled components and to find flaws in complex structures. It uses short wavelength electromagnetic radiation in the form of high-energy photons to penetrate materials and inspect for hidden flaws. Neutron radiographic testing uses neutrons in the place of photons.

Neutron radiation can pass easily through lead or steel but is stopped by plastics, water and oils. When radiation directed through the material hits a defect, it scatters. Variations in the radiation exiting the opposite side of the material thus allow quality professionals to identify the location of defects as well as determine the thickness and composition of the material.

Radiographic testing of a welded joint

Radiographic testing of a welded joint

2. UT – Ultrasonic Testing

Ultrasonic testing is used to detect defects in materials of any shape or type so long as they have smooth surfaces. Ultrasonic testing uses a transducer connected to a diagnostic machine to send vibrations/sound waves through a material. The apparatus is passed over the object being inspected. This often requires the use of a couplant (like oil or water) to connect the transducer and the object, which decreases inaccuracies and false readings in the results.

There are two methods of receiving the signal. First is ‘reflection’, where the transducer can both send and receive the signal. The other is ‘attenuation’, where the transmitter sends ultrasound through one surface and a separate receiver detects the amount that reaches the other side through the medium. Any decrease in the sound detected is caused by defects.

3. MPI – Magnetic Particle Inspection

Magnetic particle inspection is commonly used outdoors and at remote locations for detecting surface and subsurface defects. It is based on the concept of magnetic flux leakage. Magnetic flux leakage occurs when an additional north and south pole are created by a crack in a magnet. At the crack, the magnetic field bulges to form a ‘leakage’.

Iron particles concentrated along magnetic field linesIron particles concentrated along magnetic field lines

In magnetic particle inspection, a part is magnetized either directly or indirectly. Direct magnetization occurs when an electric current is passed through the test object and a magnetic field forms in the material. Indirect magnetization does not involve a current applied to the material but occurs when a magnetic field is applied from an outside source.

Since iron particles concentrate along magnetic field lines, when they are applied to the magnetized part they will cluster around a leakage.

The above three methods have different uses and require different amounts of training to complete but all will leave your part just as you found it.

In part two we discuss dye penetrant inspection, eddy current testing and thermographic inspection. In part three we discuss leak testing, guided wave testing and visual testing.


Credit: Hailey Kupiec posted on June 15, 2016 | Comment | 1241 views

Ground penetrating radar is the key to concrete cutting safety

Cracked concrete texture closeup background

Many construction outfits are coming round to the notion that concrete scanning services are vital for job safety. Whether it’s retrofitting buildings to make them earthquake-proof or ADA-compliant, or remodelling existing structures to add capacity, it is essential to know exactly how to avoid hazards that may be contained within concrete. More and more they are turning to ground-penetrating radar (GPR) scanning to know exactly where to cut and drill to reach vital building components and avoid necessary structural supports and conduit lines.

Move to improve safety in remodelling projects

Penhall Technologies is a division of California-based Penhall Company, which offers concrete cutting, coring, demolition, and repair services. Penhall Technologies specialises in GPR scanning services and has been using GPR to scan for concrete hazards in the U.S. since 2001 and in Canada before that. With a safety-driven mission and culture, Penhall considers GPR the most reliable, non-destructive way to locate targets and hazards within concrete structures prior to cutting or coring.

The company has 38 locations in 18 states and Canada, and operates across North America. They see a variety of regional building trends that affect the need for concrete scanning. In California and other parts of the West Coast, the company does a lot of scanning work for floor and wall retrofit core placement while retrofitting hospitals and universities for earthquakes. In Hawaii, their projects include beachfront property remodelling; rather than doing a full building demolition, builders strip the building down and use the concrete base to piece together an entirely new structure – one that is ADA-compliant. In addition, they scan for rebar in existing structures in cities with older buildings, for example San Francisco or Washington, DC.

“We’ve seen an increase in column reinforcement projects, where people want to add extra levels to a stadium, parking structure, or airport,” said Penhall Technologies President Simon James. “In the past they may have had to demo the entire structure and start over, but now because the engineer can avoid hazards within the concrete, they’re able to actually calculate how much weight that column can bear with extra reinforcement.”

James explains that until about 15 years ago, workers going in “blind” while cutting into existing structures often risked hitting live conduit. “Now many industry experts recognise that cutting into these hazard types can be devastating if people do not scan first. GPR technology makes the project far safer and I consider its use to be a real game-changer.” According to Penhall, structural radar imaging is a service that quickly pays for itself many times over.

Penhall has a zero accident safety culture – no accidents are acceptable. The company has established a set of safety rules, practices, and behaviours – before they even touch the equipment they are thinking safety. The process begins with site surveying, during which the GPR technician leaves the equipment in the car before the job. He has a notepad and meets with the customer on site. They discuss exactly what the customer wants to achieve. He walks around and writes down every hazard. This pre-task planning includes looking for any structural signs that may signal a potential problem. For example, if there is a horizontal beam, there may be conduit along the floor. The scanners are also looking for other trades that may be doing something unsafe near the concrete cutting area and would try to eliminate the danger.

James likens the process to the one used by detectives. “We ask them to talk to the customer and be aware of the environment, the floor, and other utility lines. They look in advance to see if there is post tension cabling, and note the gauge of the rebar – before they even get their equipment out. They can avoid a major disaster by taking these 10 to 15 minutes to scope out the job.”

They also encourage all scanners to share anything new or challenging and to contact another scanner “live” to get a second opinion, especially when as-built drawings do not match GPR data – a common issue. They have also gone directly to GPR equipment supplier GSSI when faced with unusual situations to get advice on data interpretation. The company holds internal debriefings as well as debriefings with their customer’s management team when necessary.

Getting beneath the surface with GPR

Penhall uses a variety of equipment for scanning. A large percentage of their projects are conducted using a handheld device that combines a screen and antenna in one unit. The equipment is small and lightweight, which makes it easily manoeuvrable. This is extremely important for ergonomics, since scanners can be on the job for 8-10 hours a day.

When they need to get more granular with the depth or for unusual spaces, they use a larger GPR control unit, coupled with a variety of antennas for specific needs. Examples include a 1600 MHz general purpose concrete antenna, 400 MHz utility detection and mapping antenna, and the 2000 MHz Palm Antenna, a compact, integrated concrete antenna for tightly spaced areas like corners, against walls, and around obstructions. “The ability to interchange antennas is very valuable in more complicated scanning situations, especially for in-ground utility scanning,” said James.

Data analysis is key

In addition to the actual GPR concrete scanning step, data analysis is crucial in the quality of the work and the ability to safely and accurately pinpoint hazards. “It is as important to investigate the environment we are scanning and not only understand and assess a hazard, but also to be able to evaluate anomalies in the data for potential issues,” said Elizabeth Wilson, Penhall’s Director of Field Operations. “It takes knowledge, training, and experience to correctly interpret GPR data.”

This knowledge base is enhanced by Penhall’s training and mentoring philosophy. Two-person teams include a newer employee paired with a more experienced scanner. Expert scanners from California and Toronto hubs mentor staff, oversee their work, and check results.

The company believes it takes a special aptitude to understand the science behind GPR. To get employees with the right skills, they have begun to hire from outside the construction industry, for example those with either a geology or geophysics background. They also have a very active focus on hiring veterans, including those with either non-destructive testing (NDT) or bomb disposal training.

GPR allows safe remodelling of existing structures

One example of how GPR can be used to ensure job site safety was at a major hotel, where the owners wanted to build a shopping mall on top of a multi-story compound. One option was to demolish the compound, which itself posed a host of costs and safety issues. Instead, the owners decided to actually build on top of the building by reinforcing the entire structure. To reinforce the structure, they needed to drill into the basement and install reinforcing rebar and concrete columns. “Drilling into the basement can do more harm than good,” says James. “We were able to core and scan the area. An accurate understanding of where all the existing structural elements were in the basement enabled the contractor to avoid damaging the existing structure.”

Another example is a case of a mini skyscraper in Canada in which a contractor was renovating two floors of a building and installing disabled bathrooms. Safely installing all the necessary plumbing was a challenge because the floors contained a variety of structural elements running through them, including post tension cable. James explains that cutting post tension cable is not only dangerous for the structure and integrity of the building; it’s extremely dangerous for whoever cuts it. The cables are under incredibly high tension and can whiplash. There are no drawings that accurately lay out where the cables are, or even if the cables are in the concrete.

With the help of GPR, Penhall’s staff was able to locate the precise location of existing cables and enable the cutting crew to cut safely without causing any damage. The plumbers were then able to go to the job site and safely renovate the bathrooms.

At a major university stadium project in Arizona, contractors needed to reinforce columns and required a very accurate scan of the rebar placement. To ensure the structural integrity of the columns it was critical that they not cut into the rebar, and there was little to no room for error. Penhall analysts were able to sample scan columns with precision and allow the engineers and scanning team to build a project plan that would keep the project safe and moving forward.

Much like insurance, scanning brings a peace of mind for safety and cost savings that adds the real value. The bottom line is that cutting without scanning is a gamble. In addition, doing a small sample core or cut can help solidify data found in the scan. Taking a few minutes to test an area can prevent many potentially costly losses.
Edited from source by Joseph Green. Source: GSSI

6 Myths About Hydrostatic Testing

Text appearing behind torn brown envelop - Question marks

Hydrostatic testing is a very important way to ensure that pipelines and other system parts are safe before they are installed. However, there are a lot of myths about this type of testing, and those myths can cause structural problems and put people at risk. Here are six common myths about hydrostatic testing.

During hydrostatic testing, you don’t have to remove gas tubes

Gas tubes should always be removed when doing any kind of testing. Leaving them where they can become damaged is not a good idea. It costs money to fix them, and if they become damaged and that damage isn’t noticed, they can end up being a serious risk to life and limb when the pipes or system finally goes live. By taking the tubes out during hydrostatic testing, you protect the tubes and other components and parts and reduce the risk of future problems.

You can’t test the integrity of a pipeline without hydrostatic testing

There are a lot of different ways to test the integrity of a pipeline, so you don’t have to use hydrostatic testing. It’s one option, and it’s one of the best options, but it’s not an official requirement. Other choices can be considered if there’s a reason the person doing the test would prefer to use a different kind of testing method.

If it passes the hydrostatic test, a visual inspection isn’t necessary

A visual inspection is always necessary. Passing the hydrostatic testing is important, but there should be more than one test or inspection conducted to make sure the welds are right, the pipes are holding, and all the components of the system are in full working order. A visual inspection can uncover things that other inspections or tests may have missed.

You don’t need to test at more than the system’s design pressure

By testing at 1.5 times the pressure the system is designed to hold, any problems can be located more easily. If something is going to fail, you want it to fail during the test, not during use. Using a higher pressure during the test can help ensure that any failures happen before the components are put into actual use.

It isn’t necessary to have all vents open before a test

Opening all the vents removes all the air from the pipes. The air needs to be able to escape fully before the test, so don’t leave vents closed. All the air might get out, but you’ll put a strain on the system that isn’t necessary, and that can be avoided.

You can weld after the test is performed

Welding should be done before the test is carried out, as it may not be safe to weld afterward. Making sure all the welding and other hot work is performed first can provide hydrostatic testing that is much more accurate. Finish any and all welding on the pipe system, and then perform your hydrostatic testing.


The Cool But Untold History of Ground Penetrating Radar

Antique Typewriter. Vintage Typewriter Machine Closeup Photo.No one needs to tell you that before you raise a structure, whether it’s a skyscraper or an airplane hangar or a grocery store, you’ve got to know a whole heck of a lot about the ground you’re building it on. Non-destructive testing (NDT) has a solid reputation in the construction field because it allows workers to ascertain that a particular site is stable, firm and safe … or alternatively, not.

One such NDT technology is ground-penetrating radar. You may think the name says it all, but really, there’s a lot you might not know. Here’s a brief untold history of one of the most reliable technologies in the industry.

The Application Was Obvious

You might think that when Christian Hülsmeyer patented radar back in 1904, he might first have spent a lot of time pointing it at the sky. After all phrases such as “flying under the radar” make us assume this device is most often used to locate enemy airplanes (or submarines).

But actually, radar technologies – which use radio waves – were pretty quickly pointed at the ground. As early as 6 years after the patent, Gotthelf Leimbach and Heinrich Löwy patented the first radar technology to locate buried objects.

It’s Not Just for Construction

As it happens, archeologists have also found a wide range of applications for ground penetrating radar as well: Mayan houses and platforms, burial tombs, cellars and graves, and pit dwellings are all among the scientific discoveries made using this technology to make maps of what’s beneath the surface. The military also uses it for detecting underground dangers and to avoid tunnels, among other things.

Not All Ground Is Alike

Unfortunately, you can’t just point a device at the ground and go. Well, you can, but in many cases it works better than others. You probably already know that radar relies on conductivity: it uses a wave, and that means it needs something to travel through. Soil, clay and moist materials don’t present much of a problem, and you can get a clear map.

On the other hand, dry or very sandy soils don’t conduct well. Ditto concrete, granite, cement, or other large, heavy masses. Also, ground penetrating radar works best at ranges between 20 cm to 5 m below ground, which means mapping the secrets of the Earth’s core is best left to other means.

It’s a Relatively New Construction Tool

The applications of ground penetrating radar to construction are so obvious, you might think it has always been used for this purpose, but not so. It wasn’t until 1985 or so that radar systems actually became affordable, and not until sometime in the 90s that comprehensive textbooks and knowledge bases made using them feasible.

Nowadays, ground penetrating radar is a wonderful tool in the NDT kit. Moreover, you don’t have to do it yourself. Instead, you can hire experts like Steel City, NDT, to do the job for you, making your job safer, faster and easier.

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