Over the years, the traditional techniques for inspecting small diameter piping have been X-ray or Gamma ray onstream recording and visual inspections combined with Ultrasonic Testing (UT). The emergence of Digital Radiography (DR) and Computed Radiography (CR) made the inspections slightly easier, much safer, and faster. However, these techniques remain a critical limiting factor in the practical inspection, both timewise and cost-wise. These systems are very expensive to purchase but also very expensive to operate in terms of time consumed and the personnel needed. Another technique used is UT spot-checking. In many cases, it has been used extensively as a follow-up technique or even as the primary form of inspection. While UT provides reliable results, the data gathered is limited, and the time consumed is extensive. The good news is that Phased Array Ultrasonic Testing (PAUT) for corrosion scanning has dramatically improved data quality and quantity, but the small diameters make the work rather cumbersome and time-consuming. So, suppose we assess the above available inspection techniques. In that case, we can see that the shared denominator for mitigation is consumed if we want to improve the efficiency of the inspection. Let’s take a closer look at the Beyond Current solution.
Pulsed Eddy Current
Pulsed Eddy Current (PEC) is the first notable technique and is available on Lyft®, a trusted solution for Corrosion Under Insulation (CUI) integrity management when the pipework is insulated. Leveraging a magnetic decay principle to determine metal loss, PEC has many applications in the field today. For a deeper dive into this technique, read more here.
Magnetic Flux Leakage
If the pipework is not insulated and you are looking for a reliable, sensitive, and ultra-fast (<1m/s!) screening tool, then Magnetic Flux Leakage (MFL) is an excellent method to consider. The rapid screening allows you to find the affected hot spots of corrosion, which a quantifying technique such as PAUT can follow up. Eddyfi Technologies developed Pipescan™ HD which is specifically for pipe inspections. This tool is available for all pipe sizes up to flat plates. However, the small diameter heads stand out in performance and effectiveness for this example. The heads are available in three dimensions, namely OD 5 inches (in) [127 millimeters (mm)] to flat, the middle head OD 2.8in up to 5in (37mm up to 127mm) and the small head OD 1.9in up to 2.5in (48mm up to 63mm).
MFL is a method that introduces a magnetic field into the material. Permanent magnets introduce the magnetic field in the case of PipescanHD. The magnets are designed to reach magnetic saturation within their operating limits. As soon as the tool reaches a defect, the magnetic field will be forced out of the material. Sensors can then measure this “leaking” magnetic field, and the amplitude's height will show the leaking field's strength. It is essential to mention that the spatial resolution of this tool is like no other, and therefore, minor defects will not go unnoticed!
In recent months, the PipescanHD has been trialed several times to prove its value, specifically for inspecting small-diameter pipework. Of course, the first test was done in-house in our lab. For this test, we prepared several pieces of pipework and plates, both with and without coating. The results of different defects, including Flat Bottomed Hole (FBH) defects and Round Bottomed Hole (RBH) defects, were evaluated.
The results showed that the system is very sensitive to FBH but provides excellent results on RBH, while the lift-off effect limits the result.
The PipescanHD was also used in a comparison study by the HOIS group. In this study, several techniques were tested on a spool piece. While we refer to the HOIS report for the results and complete mention of the circumstances, we can report that the tool found all the defects in the pipe spool and had 0% false calls. Also important to mention is that the PipescanHD can't be used on anything other than straight sections of the pipe. Defects in these areas were not inspected. All results from the HOIS study have been independently verified as PAUT.
The table above was published in the HOIS report, and many people are now interested in using this tool as the go-to method for screening small-diameter pipework.
Further evaluation was done with the tool on actual pipe pieces from the field. These sections showed severe pitting, such as corrosion, and the coating on the outside was not in the best condition. These circumstances have led this customer to seek inspection methods down a new avenue and use the data from the HOIS report as guidance. The results were astonishing, to say the least! All the defects found could be proven with both PAUT and MFL PipescanHD. The big difference is that the PipescanHD can inspect up to 1m/s at a coverage of 6.81 inches (173mm) on circumferential surfaces for the smallest head!
Magnetostrictive Tools for Guided Wave Testing
Eddyfi Technologies never really sticks to one solution regarding asset safety. With the recent development of the magnetostrictive tools for small diameters, we have added another excellent method to assess the conditions of small-diameter pipelines quickly. In a nutshell, referring to this blog, here is what magnetostrictive guided waves are all about.
The spatial resolution limits traditional guided wave tools and techniques, particularly for small diameters. Also, these conventional tools are limited in frequency. This made these particular tools not a popular technique for the small diameter (1.5in up to 6in/38.1 mm to 152.4 mm) lines. Now, with the magnetostrictive tools, we have taken “guided” control back into our own hands, with the availability of the magnetostrictive tools and Sonyks™. We can use guided waves in higher and lower frequency ranges (32kHz, 64kHz and 128kHz), balancing the right mix of inspection coverage and inspection resolution. Particularly on the smaller diameters, where pipe sections can be relatively short, the higher frequencies prove to be very valuable, where otherwise you would be blocked by the large dead-zone of traditional-based tools.
GMAC in Brazil
GMAC in Brazil
To gain the confidence we have in these tools today, we have rigorously tested them in our lab and in the field.
The graph below provides a basic explanation of guided waves.
With guided waves, we excite a wave in a particular manner so that its energy travels down the length of, in this case, a pipe wall. Reflectors such as welds and flanges help us understand sound energy's attenuation. This allows us to draw the DAC or Distance Amplitude Curve to assess reflector size relative to its source. If it encounters unpredicted reflectors, the amplitude will give information on its size while time travels, and it will tell us all about the location of the reflector.
In real life, it looks like the picture below:
To assess the technology internally, a special 6.56 feet-long (2 meters) pipe spool was created. This is a 4in (101.6 mm) sch80 pipe with 0.059 in (1.5mm) drilled holes around the circumference of the pipe. Also, a band of material lost was created to see the relationship between the defect and possible circumferential defects, such as can be found with under-clamp or support-type corrosion.
As we can see from the above results, the technique proved valuable.
A minor defect at 0.059 in (1.5mm) in diameter can be detected, and the focus plots quite precisely show their whereabouts on the circumference of the pipe. One of the main differences in the responses from the small holes to the band-like defect can be best seen in its focal plot. Here, you can see the energy nicely distributed around the circumference of the pipe. This even distribution can also be seen in the so-called C-scan view. The ability to call out the difference between the two responses also indicates the value of the techniques for assessing possible corrosion under clamped and traditional pipe supports.
Conclusion
The inspection of small-diameter pipework can be cumbersome and time-consuming. Although current inspection techniques are adequate and suitable, significant improvements can be made regarding inspection efficiency and data quality, specifically regarding 100% inspection requirements. Eddyfi Technologies has two techniques and products that stand out as inspection solutions for small-diameter pipework. Although these tools must be screening tools, they can quickly and confidently guide us to the locations with genuine interest.
The development in MFL pipe scanning has proven successful both under laboratory conditions and in field conditions. It shows a significant increase in time efficiency while maintaining the power of recorded inspection data. While it is not suitable for pipe features such as elbows, reducers, and tees for example, its value to straight sections of pipe with small pitting-type corrosion defects is unmatched.
The developments in guided waves for small diameter pipework with the magnetostrictive tools have already made a significant impact in the field in the short existence of today’s deployable guided wave tools. With multiple frequencies, we can find the perfect balance between the surface area covered and the measurements' resolution.
Let’s discuss how our Beyond Current solutions can optimize your next inspection campaign. Contact us for expert advice today.