Wrapping things up
Fred Starr recollects.
Before medicine was much of a science, a doctor could achieve immortality, unlike an unfortunate patient, by giving his or her name to a novel ailment or physiological oddity. Usually nothing more could be done than to watch nature take its course, but names like Crohn’s Disease, or Dupuytren’s Contracture, will live through the ages.
In failure investigation, it’s not the same. The best we can hope for is to be the first to encounter some major – but hitherto unrecognised – way in which equipment can fail. For me, this opportunity came and went when I was called along to a meeting at British Gas HQ, chaired by a rather obnoxious Yorkshireman. Although not a metallurgist, he was one of the senior figures in our London office. I was there as the company’s expert on stress corrosion cracking – accounting for most of the materials problems on our steam reforming plants. We met up with two very worried engineers from La Spezia, Italy, whose natural gas terminal was being shut down because of inexplicable stress cracking in the piping system. As the two engineers described what was going on, the more peculiar it seemed. The natural gas was bone dry, so the cracking could not come from inside the pipes. And it couldn’t be stress corrosion from wet insulation – the stainless pipes were bare. So, what was the cause? Furthermore, was there something that La Spezia could do to keep cracked pipes in operation?
In oddball cases like this – well with all plant failures, really – a visit to the site is vital. I licked my lips at the prospect. I would definitely need to stop over in Pisa, seeing the Leaning Tower. The Italians were agreeable and would cover all expenses. I was not totally surprised, however, when the chairman put the block on me going to Italy. Envy or just his normal cussedness? Gone was the prospect of fame and fun.
A few years later, there was a similar happening in a Libyan plant that did reach the literature. Like La Spezia, this facility was on the coast. Inspection showed that the pipe surfaces were picking up salt, as would have happened at La Spezia. And, also like La Spezia, the heat from the Mediterranean sun was hot enough to get the metal into the stress corrosion range. Coastal humidity came into it, too.
This couldn’t happen in this country, but stress corrosion of austenitic stainless pipework, under insulation, is quite common. A not so obvious way to stop it was to thermally spray with zinc, an idea from Dr Costi Edeleanu, chief metallurgist at ICI Billingham, home of steam reforming and the British petrochemical industry. Zinc shifts the potential. A kind of cathodic protection.
Molten zinc and the Flixborough disaster
I now make good a promise I made back in Materials World, in November 2013, to finish off my own take on the Flixborough disaster, Britain’s biggest chemical plant accident. Zinc embrittlement of austenitic stainless steel was either a direct cause of the disaster, or a contributory factor. In practice, it could only happen if, somehow, molten zinc got onto severely overheated pipe work, as was discovered at Flixborough.
In the light of this, the UK Health and Safety Executive (HSE) considered banning all use of galvanised ironwork in the chemical engineering sector. Are they serious, I wondered, given the millions of square feet of walkways, railings and supporting structures that festoon chemical plants? But I was never asked for my opinion directly.
It was Edeleanu who brought in some reality. He was incandescent at the prospect, telephoning me about what was being proposed. So much of ICI’s pipework having got the zinc spray treatment, the strictures of the HSE would shut his company down. Would I agree, he asked, that there was a far greater risk from stress corrosion than from zinc embrittlement? ‘Of course,’ I responded. Eventually, a more sensible document emerged from the HSE, but, judging from the internet, the panic and overreaction to zinc embrittlement has passed into history.
If I could travel back in time to La Spezia, I wouldn’t be using Edeleanu’s zinc spray. A few months ago, at a West Surrey Materials Society lecture, I heard a great talk from Davie McCrone of Metalyte Pipework. In cases like La Spezia, the partially cracked pipework could have been restored to full health, by winding round the pipes Metalyte’s structurally strong, resin impregnated, fibre bandages.
That wraps up, almost literally, another recollected anecdote.