Posted by GIlad Barid, VP Operations, October 07, 2019
Strict NDT specifications have been set to detect very small cracks and defects
PE piping is a durable and more cost-effective solution than metal piping. PE is a much cheaper alternative than inert metals such as copper and its low weight means transporting and installing HDPE pipes is easier and more efficient than it would be for copper pipes. In addition to this HDPE is tough, flexible and has good impact resistance meaning the pipes are resistant to external forces. This is important to avoid contamination when transporting drinking water and also in HDPE piping’s other main applications, in sewer and gas distribution networks, where leakages would be highly problematic.
The pipes themselves are prefabricated into units which are then pieced together to give the desired overall structure. Each individual pipe unit is then welded together, using metal connectors, to make sure the system is watertight. The joint, where two individual units are connected together, are the weakest parts of the piping system. It is at this point where most leaks and breakages of the pipe occur, which can be the result of an improper weld or a defective pipe structure. To determine the cause of any weaknesses the thorough inspection of the pipes is necessary.
“We’ve found that digital radiography is the method that works the best overall for our pipe inspections”
How to inspect HDPE pipes welding?
As we don’t want to cause any unnecessary damage to the pipes we use a non-destructive testing method. We’ve tried several different techniques for non-destructive testing such as digital radiography, which is a form of X-Ray imaging, ultrasonic flaw detection, which uses sound waves to detect structural anomalies and microwave imaging which, as the name suggests, uses microwaves to detect flaws. None of the techniques are 100% perfect but we’ve found that digital radiography is the method that works the best overall. As a result of this we now use digital radiography for all of our pipe inspections.
What types of defect does digital radiography allow you to observe?
Digital radiography allows us to observe any errors in the joining of two pipe units such as imperfections in the weld, misaligned pipes or incorrected insertions. The system can even image dirt that may be disrupting the weld quality. We can also see structural flaws in the pipes themselves, which can be inherently problematic, such as impurities or defective regions containing pores and voids. The inspection system can also find any cracks in the pipe, even if they are invisible to the naked eye. This allows potential problems in the pipes to be spotted prior to their installation.
What are the other advantages of digital radiography over ultrasonic and microwave technology?
The biggest advantage for us is that the radiographs (images produced by the instrument) are very easy to understand. This means that a non-NDT expert can look at and understand the images. This saves us a lot of time when communicating problems with installations to other contractors who are working on the same project as us. This is not the case for ultrasonic flaw detection or for microwave scans which give complex images which take a level of skill to correctly interpret. Also, it’s worth mentioning the huge range of different flaws and defects that digital radiography is capable of detecting and distinguishing between. This allows a comprehensive analysis of the weld and pipe condition without having to use multiple techniques.
What digital radiography system do you use?
We use the Vidisco DRT system with a FlashX Pro panel alongside an Yxlon Evo 300 kV x-ray tube as an x-ray source.
Why did you choose the Vidisco FlashXPro as your digital radiography system?
It is the best system on the market for a number of reasons. The FlashX Pro panel provides a large image area with a high resolution. This is really important to us as the HDPE joints that we inspect can be of a large diameter (up to 1,200 mm) so we need large images to allow us to inspect the entire pipe. The high resolution means that whilst we can image the entire pipe joint we can also be able to detect small defects which could become problematic at a later date. Additionally, the FlashX Pro has a range of other features which make it desirable for use in the field. It’s highly portable and has WiFi capability which means the transfer of captured data is straightforward. The systems power cable has been designed for use in harsh environments and can transfer both data and power over a range of 50 meters.
How easy have you found it to use digital radiography and the FlashX Pro in particular?
As the technique involves the emission of x-rays, digital radiography requires a trained and skilled operator. However, even with this in mind, the technique takes less delivery time than ultrasonic and microwave inspections so we would still recommend it. Also, as digital radiography is such a common technique for the quality control and analysis of metallic joints there is no shortage of skilled operators who could help with your inspections, which is not necessarily true for professionals in the ultrasonic and microwave spaces.
Where can our readers find out more about Inspecta, your studies on digital radiography and Vidisco?
The best place to look for our work on pipe inspection would be our website.