Chesterfield Special Cylinders’ Integrity Management team (CSC IM) has welcomed DNV GL’s move to make acoustic emissions (AE) testing the preferred method for carrying out periodical inspections of seamless gas cylinders.
The classification society is the first to include AE testing in its set rules, aligning it with a new European standard for gas cylinders and their periodic inspection and testing (EN 16753), which was introduced in 2016 and favours the AE method.
Experts on AE testing at CSC IM have long argued that hydrotesting, a method where the integrity of seamless gas cylinders is checked by filling them with water, is slower, less safe and more expensive.
AE testing negates the need for the potentially dangerous pressurising of the tubes to up to one and a half times the pressure for which they are manufactured, as hydro tests do. Nor does AE require the introduction of water into the tubes, a lengthy and potentially damaging process, nor the drying of retained water. AE testing is also conducted without removing the cylinders from where they are installed.
AE is safer, faster, cheaper
Stephen Butler, Director at CSC IM, explains, “The new DNV GL offshore diving guideline says AE testing in lieu of hydrostatic testing of gas storage tubes is accepted, provided the testing is carried out in line with EN 16735.
“We believe AE is safer, faster and cheaper than traditional hydro testing. End users who start to adopt AE instead of the outmoded hydro test, will benefit from safer and faster tests as well as reduced budgets,” Butler adds.
Arnfinn Hansen, Principal Engineer, Offshore Equipment and Diving at DNV GL, explains, “AE testing uses sensors mounted on the cylinder to ‘listen’ for cracks by detecting so-called elastic waves.”
“These types of cylinders can carry up to 3000 litres of compressed gas, so not having to fill them with water is more time-efficient, and it also reduces the risk of causing the cylinder to rust,” Hansen continues.
Butler is confident that owners and operators worldwide will adopt AE and make the current trend for hydro testing obsolete, “Hydro testing is increasingly seen as less safe and more costly,” he says. “Now that AE techniques have been developed — in line with the hi-tech nature of other NDT techniques — and global authorities such as DNV GL are recommending them, I have no doubt that hydro tests will become a thing of the past.”
It is predicted that end users of new cylinders will now only use AE tests so that water is never introduced into them. For older dive systems that have previously been subjected to hydro tests and related cleaning processes, AE tests will assure the end user of the integrity of these aging products.