The Magazine for Underwater Professionals

Nov/Dec 2017


Association of Diving Contractors

Ten years can mean a lifetime for your average HP storage cylinder

Depending on your perspective, the last 10 years to some will seem like a short period of time, to others it might feel like a lifetime. Speaking personally, for me it has been a magical period.

A decade ago, after four years as the ADC secretary, things were starting to make sense, the varied workload of the Association appeared to be almost under control, and things were generally starting to look up. Confirmation of the appearance of a first grandchild had just occurred, so spirits were high. At the time, I had no idea how special it would be to have a little playmate around, that thought alone cheered the bleakest winter day, and the reality that would appear in July the following year was even better than I could ever have imagined.

Few of us had any real idea about what was going to happen to the economy. Some of the financial pundits had noticed odd things occurring in the markets and their reports were starting to spread around the media, but we all had to wait a few more months before the real crunch got underway; interest rates started to plummet, austerity began to set in and belt tightening became the norm. The years of bouncing along at near zero interest rates were soon to be upon us.

Consider then the life of the humble HP spread storage cylinder. Ten years ago, most would not have been new – a substantial number would have already seen extensive service in other industries, many with the Ministry of Defence – but by whatever convoluted acquisition route, they were now in your keeping and were a most valued part of your essential support equipment.


Daily life for the average storage cylinder to some could seem a bit bland. Static for most of the day, occasionally being moved around, rolled sometimes, manhandled roughly at other times. Subjected to filling and draw down cycles on most days, getting hot and bothered during the fill cycles, sweating and cooling when in use, with frequent expansion and contraction events testing the quality of your metal on a daily basis. And then periodically being opened up for close inspection, being probed, prodded, rolled and scratched, and even getting a bit of a touch up on the paint front, before more filling and depleting cycles started once more. On top of all that, when being moved around and transported, the support arrangements can sometimes be less than delicate.

Is it any wonder then that every now and then something untoward happens. For a long time, we have all come to accept that the HP storage cylinder is a tough bit of kit. Probably over designed, or so we assume, but able to take a fair bit of punishment and to just carry on doing what it is supposed to do, accepting and then supplying HP air. However, when one does rupture the fall out can be dramatic. Humans are not so robust, so when things start to fly around after an HP cylinder has ruptured, serious injury can and does result.


Ten years of operational use for the average HP storage cylinder can be a long time. Their care is probably not as high on our attention list as some would like. Frequent harsh handling is the norm, we rarely think about the changes that can be taking place in the metallurgy as we fill and deplete without much thought – sometimes using dry air, sometimes introducing a bit of moisture to the mix to accelerate the process of degradation. And then to cap it all off, after periodic testing at our usual place, at the 10-year point a different VCA test centre is likely to be required to ensure we comply with the requirements of the current ADR.

Looked at in this manner, retaining cylinders that are more than 10 years old starts to be questionable. If the regime to test, inspect, handle and monitor is robust, then a safe operational life beyond 10 years is probably doable. How far beyond can only be determined by a whole host of variable elements.

However, if a more honest spin is put on the life of a cylinder, we buy it, generally do the minimum testing, inspection and maintenance to keep it functioning and operational, and pretty much expect it to continue providing what we need almost indefinitely. Recent events changed all that. HP cylinders that are reaching the end of their life for whatever reason are highly dangerous. In an industry sector that has worked hard to improve safety standards, getting to grips with the real risks associated with aging HP cylinders needs to get more attention. For a professional business to make a plant investment and write the value over 10 years and then replace would probably be the wise choice.

This will probably be my last article on behalf of the Association. When I first started writing them, the process seemed quite daunting. But over the years it has got a bit easier; sometimes a little off track for some people, but hopefully helping to the get the key message across. Inland/inshore diving does not have to be dangerous. Select the right professional diving contractor, plan, prepare for and risk assess the work anticipated and use divers with the required skills, and diving can be progressed safely with outcomes above the acceptable standard – despite the low visibility, cold water, current flow, equipment restrictions…


Roger O'Kane





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