Rust caused by water left in cylinder after hydro test
With the rise in popularity of AE testing for seamless gas cylinders many experts are predicting that hydro testing will soon be phased out. DNV GL says AE testing is more time‐efficient and reduces the risk of causing the cylinder to rust.
Arnfinn Hansen, Principal Engineer, Offshore Equipment and Diving at DNV GL, says: “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 water, so not having to fill the cylinder with this volume is more time‐efficient, and it reduces the risk of causing rust.”
Safer, cheaper, faster
AE is considered safer than hydro because it does not require the potentially dangerous pressurising of the cylinders to one and a half times the pressure for which they are manufactured; and does not require the introduction of water into the cylinders. Hydro testing’s repeated insertion and removal of test fittings also brings the risk of thread damage.
AE testing flags up warnings of defects which may be acceptable now but which can develop into safety issues in the future. With AE they can be measured and tracked but hydro often masks such issues.
Given the drive to maximise income, many owners and operators need their cylinders inspecting and testing quickly, when their
Society of Maritime Industries Annual Review 2018
certification is due to lapse. The start‐to‐finish AE project is usually faster than the hydro test process and AE testing can be conducted in situ with the ship still in operation.
Also, whatever effort is put into drying cylinders after a hydro test, there is often residual water in the vessel to be removed with further purging – this can require additional work to clean the corrosion through shot blasting, flailing or acid cleaning. This can even leave residual acid in the cylinder, requiring yet another flushing process.
Those predicting that AE will replace hydro worldwide also point to longer‐term cost benefits, such as the rapidity of the process and the potential for extending the life of the cylinder itself.
It is also predicted that cylinders in new installations will only ever have AE tests, so that water is never deliberately introduced into the system.
For older systems previously undergoing hydro tests and related cleaning processes, AE tests will assure the end user of the integrity of these aging products by confirming the absence of growing fatigue cracks.
Stephen Butler Director of Integrity Management, Chesterfield Special Cylinders Limited. Members of the Society of Maritime Industries (SMI)
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