Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/755145
18 WET NEWS DECEMBER 2016 Regular inspection of tanks is essential to identify any potential for future leaks, arising from corrosion, damage or insufficient material thickness or strength. Testing conditions for tank testers INSIGHT Insight Tanks & storage I n addition to the financial implications of the loss of product, leakage from storage tanks can cause serious environmental damage and represent a grave threat to health and safety. In some circumstances, particularly when the stored materials are combustible or explosive, leakage can result in a major incident involving the loss of life and substantial damage to assets and to an organisation's brand. The variability in tank type, age and condition means that a wide variety of technologies are required to conduct effective inspections. The data derived from this work is used to inform an effective tank maintenance, repair and replacement programme. A rigorous inspection programme there- fore reduces risk and avoids downtime; protecting sites from environmental and safety impacts, and the costs THE CONCEPT • A 'launch tube' was built on one of the roof's purge points • Pearpoint P374 camera system was used to inspect the AD tanks • The Ectane is a multi- technology test instrument NEED TO KNOW 1 The variability in tank type, age and condition means that a wide variety of technologies are required for inspections 2 A rigorous inspection programme reduces risk and avoids downtime 3 Data is used to inform an effective tank maintenance, repair and replacement programme THE VERDICT "Every tank is different; not just in age and material of construction, but also in build quality and operational conditions. The environment can also have a significant impact on tank quality and integrity, as can operational conditions" Steve Drake, Ashtead Technology Tank inspection engineers can ensure that all potential risks are assessed, and that inspection frequency is optimised to minimise costs associated with decon- tamination and clean-up. Steve Drake, Ashtead's NDT market manager, believes that the most efficient approach to the maintenance of tank structural and operational integrity is based on a flexible non-intrusive inspection programme. He says: "Routine calendar-based inspections that rely on historical data, such as fabrication material and age, risk ignoring current conditions and environmental factors. In contrast, we have customers using a range of inspection instrumentation that enables the assessment of current tank condition, oˆen without interrupting tank service, so that an appropriate inspection frequency can be determined. "By employing a range of technologies, inspection engineers can ensure that all potential risks are assessed, and that inspection frequency is optimised to minimise costs." Inspection also helps demonstrate compliance with relevant standards and codes, and provides reliable data on tank capacity; ensuring safe storage of materials such as chemicals, petroleum products and liquefied gases in both underground and above ground tanks. Anaerobic digestion A wide variety of technologies are employed for the inspection of tanks, and these instruments are amongst the most popular in Ashtead Technology's fleet of rental equipment. The company's customers can select instruments for Non Destructive Testing (NDT), providing data for thickness, corrosion, cracks, flaws and weld integrity. Remote Visual Inspection (RVI) instruments are also available to inspect the difficult to access locations that exist inside most tanks. An Ashtead Technology customer was contracted by a UK utility to inspect its anaerobic digestion (AD) tanks. In applications involving potentially explosive gases, an intrinsically safe certified push- rod inspection camera is recommended. Following the development of a customised access point, inspection engineers could produce comprehensive images and videos showing the condition of the digester's roof and walls. The tanks were fabricated in GFS (Glass-Fused-to-Steel), a material which combines the strength of flexibility of steel with the corrosion resistance of glass. Consequently, GFS is commonly employed in applications with aggressive environments such as those inside anaerobic digesters – high temperature, high humidity, methane and hydrogen sulphide. An intrinsically safe Pearpoint P374 camera system was used to inspect the AD tanks, in conjunction with a digital video recorder. Costs A customised 'launch tube' was built on one of the roof's purge points, and nylon attached to the camera tip so that every surface could be videoed once the probe was lowered into the 'live' digester. The survey results demonstrated the condition of the tank very effectively, without having to decommission the digester, helping to keep costs to a minimum. A chemical manufacturer in the North-west had a requirement to inspect a large stainless steel vessel. The contents of the vessel were typically saline and varied between 50° and 100°C, so the site managers were concerned that stress corrosion cracking might be a possibility. Inspection engineers believed that Eddy Current Testing with the Eddyfi Ectane Surface Inspection System Ectane would be ideal for this application, so an Ectane was taken to the customer's site to provide a demonstration. To test the Ectane's ability to detect stress corrosion cracking in 10mm stainless steel, the client provided a test sample for inspection, and a flaw was correctly identified. The Ectane is a multi- technology test instrument, and in addition to Eddy Current Testing, it is also able to perform Eddy current array (ECA), Remote-field testing (RFT), Near-field testing (NFT), Magnetic flux leakage (MFL) and Internal rotating inspection system (IRIS) ultrasonic tube testing. The external inspection of the vessel took around two hours, and covered a surface area of around 16m2. The vessel was found to be free from any detectable stress corrosion cracking. Ashtead's fleet of rental instrumentation also includes some of the latest technology for fast, effective tank inspection. Silverwing is a leading manufacturer of NDT solutions for storage tanks, vessels and pipe inspection, and has appointed Ashtead Technology as its Preferred Rental Partner in the UK. The Silverwing products offer motorised magnetic inspection; the Scorpion for example, can inspect vertical, curved and even overhead surfaces. Drake says: "Every tank is different; not just in age and material of construction, but also in build quality and operational conditions. The environment can also have a significant impact on tank quality and integrity, as can operational conditions. "It is vitally important that all potential risks are assessed, which is why we offer such a wide range of the latest technologies; offering customers the opportunity to make sure that they use the most appropriate inspection tools for every tank or vessel."