The new ISO 6406 standard cuts the allowed general corrosion and line corrosion tolerances on cylinder casings from 25 to 10 per cent, while isolated pit corrosion tolerance is cut from 40 to 20 per cent.

Geoff Cutler of Q Tech Solutions says this has raised new questions about the lifespan of cylinders and the associated safety, legal and commercial implications.

'In the gas cylinder industry there is factor known as \\$quot;˜missing cylinder syndrome\\$quot; where the owners just do not know or aren\\$quot;t bothered where some cylinders are. Thousands of untracked and unmonitored cylinders \\$quot;˜disappear\\$quot; in the constant exchange of equipment and end up unaccounted for.

'End-users continue paying rental on these missing cylinders and this is used as a bargaining chip when negotiating new supply contracts, with cylinder owners offering to write these off. Alarmingly, the written off cylinders can remain in use for years afterwards without undergoing the legally required regular maintenance checks or recycle through other suppliers and this is serious safety issue.'

Deadly explosion

The unmonitored cylinders have become the responsibility of the operator and a serious liability under corporate manslaughter laws and commercial obligations.

According to Cutler, unmonitored cylinders are a big problem, particularly in West Africa and in countries where health and safety issues are not taken that seriously.

'I am surprised that some of the major companies are willing to take a chance and hope that nothing goes wrong. I have seen a 15-year-old cylinder filled with water explode under testing conditions. If this explosion happened when the cylinder was full of gas it could have caused a serious injury, even a death.

'There are cylinders that are up to 60 years old. Unfortunately most of the accidents haven\\$quot;t been reported very widely. An unsafe cylinder full of a high-pressure or combustible gas is a time bomb \\$quot;“ literally.'

Responsibility is the answer

Unmonitored cylinders and the gas they contain can pass their \\$quot;˜use-by\\$quot; date with nobody noticing and if they fail, the operator can be liable. The practice of writing off also means the cylinders become untraceable in the event of faults being discovered in any component, including valves and regulators.

Cutler continues: 'Owners of the cylinders should take more responsibility. There are many old cylinders circulating that can be re-used but they need to be traced and re-tested in order to make sure they are safe to use.'

'Faulty gas cylinders, regulators and valves, as well as non-conforming gas products, have a high potential to cause serious injury and even death. Companies writing off this equipment should be more concerned with locating and maintaining these cylinders \\$quot;“ not rolling over contracts.'

Dominion Technology Gases general manager Paul McAlister admits that missing cylinders are dangerous and that a company would invite a catastrophe to its customers if they offered to write them off without attempting to locate them.

He said: We have specifically developed CATS, cylinder asset tracking system, to electronically monitor every movement of each cylinder so that we meet our obligation to the standard.'

The new standard recognises the lack of stringent quality monitoring and is seen by industry insiders as an attempt to reduce the risks by imposing a shorter \\$quot;˜shelf life\\$quot; on cylinders. It replaces BS 5430: Part 1:1990. Both are titled \\$quot;Periodic inspection and testing of seamless steel gas cylinders'.

Worthington Cylinders former technical director Gerhard Konig says the new ISO 6406 has to consider the latest state of technology in cylinder making and has therefore taken into account that thin wall, high strength and highly stressed cylinders are in service.

He said: 'With such cylinders ISO TC58/SC4/WG1 did carry out their tests with different simulated corrosion defects. Based on these results and the fact that retest periods have been prolonged in the recent years (e.g. for OXYGEN from 5 years to 10 years).

'In other words, the time that corrosion can take place and attack the cylinder wall in that case is doubled. Therefore a reduction of the permissible corrosion depth is in my opinion justified to guarantee adequate safety for the next period of ten years. This theory is valid for old cylinders as well as for new ones.'