One of the major advancements that has raised the bar for EMI inspection capabilities focuses around solid state hall sensors. When inspecting OCTG tubing and casing, it is a common practice to utilize magnetic flux leakage inspection techniques. The primary objective is to fill the entire pipe body with enough magnetic flux, that any flaws on the ID or OD pipe surface will cause a disturbance in the magnetic field that can then be detected by sensors and reported through software to the quality personnel for further investigation.

The magnetic field moves from north to south poles through the tubing or casing. When the magnetic field encounters a break of some kind in the material under inspection, i.e. an imperfection in the ID or OD surface of the pipe, the magnetic field will jump from one side of the imperfection to the other, in order to return to back to the ferrous material on the other side and continue its journey to the opposite pole. This jump, referred to as a perturbation, is the magnetic flux leakage that ultimately escapes and what will need to be picked up by the sensors, and reported to the operator, notifying them that further investigation is needed on that joint of pipe.

Over the years, Scan Systems has helped further technological advances in the NDT inspection industry by continually updating and innovating their products and equipment, specifically our PITCO inspection equipment, to help achieve more efficient and accurate solutions. Through these advances in the industry, different variations of sensors were created to detect and report on the flux leakage created by the imperfection in the pipe.

The most common sensor type is a wound induction coil, sometimes referred to as a wound coil or PC coil. The wound coil has been used in the industry for over 60 years and has a solid track record of performance. While consistently used, there are limitations to this 60 plus year old sensor technology:

  1. To achieve the best results with his type of sensor, the angle of intercept of the potential flaw and the sensing coil must be at a 90º angle. Meaning if the flaw or imperfection itself is off the axis being inspected by more than a few degrees, many EMI inspection systems will never detect that flaw.
  2. Wound coils are speed sensitive. The size and amplitude of signals detected are surprisingly dependent upon the speed the flaw intersects the sensor coil. This makes repeatability tolerances difficult to narrow as the same flaw can exhibit totally different characteristics with only a small variance in linear speed. This technology has a greatly diminished value in slower production lines.

In the early 80’s, the NDT (Non-Destructive Testing) industry explored several alternatives to the PC coil. Magnetic Diodes, Emats, and hall elements being the primary subjects of study. All of which proved to have substantial drawbacks when used in daily operation. But advancements were made, and in the mid 1990’s there were some major changes, to hall element sensor designs in particular. The greatest drawback to the early hall sensors was their heat sensitive nature. If they got too hot, they gave erroneous data, or simply failed.

With the invention and implementation of solid-state devices, which mitigates the issues with heat, solid-state hall sensors became a product that could be brought into production environments. The benefits include:

  1. The hall sensors have a 360-degree sensing area, as opposed to the 90-degree sensing area of the PC coils. This allows imperfections disturbing the magnetic flux to not have to be at 90º to achieve acceptable results. Now flaws can lay as much as 30º of the inspection axis and still be reliable identified.
  2. Hall sensors are not speed sensitive and thus allow for significant variations in the production line speeds. Without speed affecting the frequencies and amplitudes of the signals repeatability is now greatly enhanced and more reliable.
  3. Hall sensors have unique signature. The frequency and amplitude of the signal that is picked up by the sensor, is a unique signature that allows us to employ software algorithms that now can be easily identify and separate the signal for further processing and reporting. This has lead Scan Systems Corporation to greatly reduce many of the limitation of EMI inspection that we have been battling for decades.

The evolution of the sensors is a testament to the fact that standard technologies in any industry, specifically the EMI inspection industry, should be challenged and evaluated all with the goal of seeking more efficient and more accurate technologies. Scan Systems’ PITCO Division has improved and evolved their equipment over the years to better serve the OCTG industry’s inspection needs. Through these enhancements, Scan Systems is paving the way for more advanced equipment providing for a safer industry.

We can all agree with Investopedia that quality control is “the process through which a business seeks to ensure that product quality is maintained or improved and errors are reduced or eliminated.” This definition spans all industries, but the criteria by which companies pass or fail a product is a different story.

Many OCTG MFL (magnetic flux leakage) inspection equipment manufacturers claim their machines detect flaws on 0.545” (13.84mm) walls and greater during the inspection process, but often these claims ignore a key component of a quality inspection – repeatability.

API 5CT specifications require a minimum of 20% repeatability on all inspection runs. Oftentimes the detectability specifications given by EMI vendors to the steel mills, processors, or inspection companies are a reflection of the equipment manufacturer’s upper limits of detection capabilities, or best case scenarios—and they hope to address the repeatability of their equipment much later in the vendor selection process. “In our opinion, there needs to be more focus on repeatability much earlier in the technical evaluations” said Danny Uselton, President of Scan Systems Corp.

In EMI inspection, repeatability comes down to the equipment’s hardware and software capabilities to identify the signal given by an imperfection or artificial reference indicator and report those imperfections at a similar amplitude… consistently and repeatedly. The long and short of it is, the equipment must have the capability to pick up the flaw and break the alarm threshold each and every time in order to provide the level of confidence in the inspection that API requires. If the signal from a flaw falls within an area of significant noise generated from the pipe, it may stand out during one pass (detected), but get lost “in the grass” during the next run (repeatability). Using advanced signal processing algorithms combined with proprietary sensors and cutting-edge signal detection hardware, Scan Systems’ PITCO M-Series with ESP upgrade has dramatically improved the ability to separate a flaw’s signal from the background noise offering the best S:N ratio on any given pipe in the industry.

For Matt Rutledge, General Manager/VP of Scan Systems, repeatability is a top priority and something customers should ask about sooner in the vendor selection process. “Surprisingly, many steel mills, processors, and third party inspection companies neglect to inquire about the inspection equipment’s capabilities in regards to repeatability until much later in the selection process.”

While 0.400” (10mm) pipe wall thickness has historically been the limit for existing EMI/MFL inspection equipment, Scan Systems’ PITCO M-Series with ESP upgrade can reliably detect and repeat on N5 ID notches up to 0.545” (13.84mm) wall thickness and N10 ID notches up to 0.625” (15.875mm) walls. This ability to accurately detect and repeat on these types of indications is truly a remarkable accomplishment by the employees in the R&D department of Scan Systems Corporation.

When equipment vendors quote specifications that exceed the known capabilities of EMI equipment currently in operation, the best thing for you to do is ask the vendor to demonstrate their claims. Danny Uselton commented, “At Scan Systems, that is how we separate ourselves from others who claim similar capabilities who don’t think they will ever have to prove it. We love demonstrating our systems’ capabilities and explaining the processing software and sensor technology we have developed to advance our industry.”