In the next snippet from our most recent eBook on ‘Ultrasonic Thickness Gauges in Potentially Explosive Environments’, we look at the areas in which you can use a tool like this and why there are requirements for them to be intrinsically safe.
Using an ultrasonic gauge for corrosion testing is a lot more complex than other types of testing, which means that a more capable device is required. Corrosion testing generally requires the transducer to be moved in a snake-like motion within a 100mm x 100mm box on a specific area of interest. This can be seen in the diagram below.
The device will monitor the thickness reading across the path and provide the user with a maximum, minimum and average reading. This type of reading gives a clearly defined area within the pipe wall that is thinning quickly and easily.
Handheld UT devices designed for NDT inspections generally operate with transducers in the region of 2Mhz -> 10Mhz. A rule of thumb for transducer selection is higher frequency equals higher resolution. For thin-film or high-accuracy coating inspections, a 7Mhz transducer is usually the best choice, whereas for depth penetration, a 2.5Mhz transducer is selected. For standard NDT and corrosion inspections, a 4Mhz transducer will provide optimal depth penetration with an accuracy of 0.1mm.
Areas of use
Classified or hazardous locations are a prime example of the application of ultrasonic NDT. Pipelines located within petrochemical facilities, both on and offshore, represent an ideal environment for using ultrasonic gauges for basic thickness measurement, through to corrosion, weld and flaw detection.
Why? Because ultrasonic gauges in highly corrosive offshore installations can help prevent pipeline failures by providing the information required to schedule planned maintenance. Operations thereby avoid unplanned maintenance due to failure.
However, classified locations present their own particular problems, in that devices used within these potentially explosive atmospheres must comply with legal requirements designed to prevent explosions. These requirements apply to ultrasonic gauges in the same way as multi-meters or other IS devices, with the added complications of the higher voltages required to excite the transducers and the power generated by the transducers themselves; even if disconnected from the pulser or receiver. The commonly used term for devices certified for use within these areas is ‘intrinsically safe’.
So, what are the intrinsically safe requirements? Well, intrinsically safe devices are designed to limit power both at the source, which is the battery, as well as at component level to prevent a spark or heat powerful enough to ignite a gaseous atmosphere. Even the casing and neck strap of an intrinsically safe device must be manufactured from a certified anti-static material to prevent a spark.
Ultrasonic gauges that are intended for use within hazardous or classified areas should comply with these specific requirements and come as fully-certified as intrinsically safe, based on third-party standards such as ATEX and IECEx.
For a more in-depth view of ultrasonic testing using intrinsically safe devices, download our FREE eBook below:
Ultrasonic Thickness Gauges in Potentially Explosive Environments.