Non-Destructive Testing: Various Approaches used in the Oil and Gas Industry
Oil and Gas pipeline data from 2010 to 2018 revealed that in the United States, there were close to 600 injuries to oil and gas industry personnel, over 125 deaths, over $4 billion in damages, more than 800 fires, and 300 explosions. If there is one thing self-evident about this data, these pipelines, which span thousands of miles across the country, pose a constant threat to life and property. The only way to ensure they are in top working condition is through rigorous testing and maintenance routines.
Introduction to Non-destructive Testing
Like other industries, in the Oil and Gas sector, one important technique used for testing is called Non-destructive Testing or NDT. In this post, we will take a deep dive and discuss NDT on the different types of NDT.
The Oil and Gas industry is accountable for the proper upkeep and maintenance of pipelines and is governed by several industry regulations, codes and laws. In addition, organizations like the ASME (American Society for Mechanical Engineers) and the API (American Petroleum Institute) define several standards to be followed, many of which outline approaches and standards for NDT.
What Is Non-destructive Testing?
Let’s first understand what NDT is. Non-destructive testing (NDT) is an inspection and testing method used to assess gas pipelines’ material and condition. Unlike destructive testing, which damages the tested material, NDT has no negative impact on the system. This means that NDT is preferred over destructive testing methods since it ensures that costs are kept down, and assets are retained intact. Safety is another critical benefit of NDT. Except for Radiographic Testing (RT), most non-destructive testing methods pose no threat to inspectors and technicians. NDT has also proven to be a faster and more accurate method, yielding consistent results and being more reliable in the long run. Because of these tangible advantages, NDT is used across a spectrum of industries spanning Oil & Gas, Mining, Automotive, Power, Chemicals, etc.
The ASNT (American Society For Nondestructive Testing) outlines protocols to be rigorously followed, ensuring that assets like gas pipelines posing high risks are inspected by certified inspectors and often approved by certified witnesses from designated inspection bodies.
NDT Test Methods:
Let’s look at some of the popular approaches of NDT employed in the Oil and gas sector.
Magnetic Particle Testing (MT)
Magnetic Particle Non-Destructive Testing helps trace defects in a material by locating disruptions in the flow of an induced magnetic field. Usually, inspectors place iron particles on the material surface and can quickly spot imperfections in the material based on the visual indicators evident in the particles.
In one technique of Magnetic Particle Testing, a Central Conductor charged with high amperage is used to create a circular magnetic field in the cylindrical pipeline structures. This circular magnetic field exposes longitudinal defects as well as radial imperfections.
Liquid Penetrant Testing (PT)
Liquid Penetrant Testing also referred to as Dye Penetrant Non-Destructive Testing, is one of the NDTs conducted by inspectors. They cover or coat the material being tested with a liquid, either regular or fluorescent dye. They spot “breaks” in the liquid, which indicate faults, cracks, and weaknesses in the surface. Inspectors use substances called developers to extract the penetrants from the defect areas and then map the defects. When fluorescent dyes are used, they use ultraviolet light to locate and examine the defects.
PT Techniques include the use of different types of penetrants.
- Water-washable: One common type is water-washable penetrants. They are used mainly for objects with rough surfaces, holes, grooves, etc., and can be easily removed using either a water spray, air agitated immersion, or manual wipe. They are also often referred to as self-emulsifying systems.
- Post-emulsifiable: Post-emulsifiable is another type of penetrant used. The advantage is that this type of penetrant can be used when water washing cannot be because of concerns that over-washing may adversely impact the material. These are suitable for smooth surfaces. They need different emulsifiers that break down the penetrant to be washed off more easily.
- Solvent Removable: These penetrants need solvents to dislodge them from the material. Companies also use Lipophilic emulsifiers, oil-based ready-to-use materials, and Hydrophilic emulsifiers, which are water-based and used as a concentrate diluted with water.
Radiographic Testing (RT)
Radiography Non-Destructive Testing is one more prominent method of non-destructive analysis. This technique uses X-rays or gamma rays to scan the material and identify imperfections and defects not visible to the naked eye; they can even spot minor alterations in the density of the material. This approach relies on using a radioactive isotope or X-ray generator to create and capture images of the material, revealing intricate details and enabling thorough material analysis.
There are several Radiographic techniques employed in NDT in the oil and gas sector. Some of the more commonly used methods include:
- Computed Radiography: Computed Radiography (CR) is an X-ray or gamma radiation technique. The main distinguishing feature is replacing traditional X-ray film with digital technology. An imaging plate captures the image, and a scanner digitizes it for image processing. The plate is reusable, making the process faster and less expensive.
- Computed Tomography: Computed Tomography (CT) is often referred to as Computerized Axial Tomography (CAT). It leverages specialized X-ray equipment used for NDT inspection to help identify and size planar volumetric details in three dimensions. The X-rays help create measurements which are then used to develop reconstructed digital images.
- Digital Radiography: Digital Radiography equipment entails a higher initial investment than technologies like Computed Radiology. However, it is a highly advanced technology that enables the instant production of an x-ray image on a computer. The method is applicable primarily to determine wall thickness details, detailed measurements, an inspection of corrosion under insulation (CUI), electronics parts, etc.
- Film Radiography: This technique uses a silicon film on which the X-rays capture an image. It is primarily used for volumetric inspections. This method of RT helps with inspections of a range of materials with different levels of density and identifies corrosion, damage in composites, fabrication flaws, etc.
- Ultrasonic Testing (UT): As the name indicates, this technology relies on high-frequency sound waves in methods like pulse echo for advanced imaging of pipelines. Here inspectors transmit sound waves into the material and can identify flaws and defects based on the echo patterns produced by the sound waves.
As we have seen, these are some of the commonly used NDT techniques. Using several of these methods of non-destructive testing, oil and gas companies can ensure regular inspections, detailed analysis, and thorough maintenance of their gas pipelines with zero impact on their infrastructure.