Fred Starr recollects: Nature on our side

Materials World magazine
,
8 Apr 2013

It is a truth universally acknowledged, among metallurgists at least, that almost every metal has to be fought for. Apart from gold, metals must be smelted from their ores that themselves need to be upgraded, before being subjected to the blast furnace, the electric arc, or the electrolysis bath.  

It is also universally acknowledged that once we have got metals into a useable form, nature has still not finished with us. Given the time and opportunity, everything we make will turn back into a misshapen lump of oxides, carbonates, sulphides or sulphates. It is not just golden lads and girls and chimney sweepers that come to dust! But the fight to stop materials going back to their natural state provides gainful employment for many people. I, too, have been at the sharp end in the army of corrosion engineers.  

Stick around in any job and what goes around comes around. What was at the time a perfectly sensible set of anti-corrosion procedures came back to bite me and John Thurley years later. Who is John Thurley, you might ask? Given that Britain now imports about 20% of its gas in liquefied form at -170°C, you should. John’s company helped develop a means of evaporating LNG and delivering it into the gas pipeline network. Back in the 1960s, British Gas was one of the first operators to make use of the technology, and this blindingly simple concept is still used throughout the world. In the Thurley evaporator, LNG is pumped through a nest of stainless tubes that are immersed in a bath of water. The heat in the water is transferred to the LNG where it evaporates. The clever part is to have high velocity gas burners blasting down into the water, keeping it warm.  

I met John in 1969 when we fixed up a set of anticorrosion procedures for his evaporators at Canvey LNG Terminal. That was that until 1982, when he rang up asking if I would drop everything and go to Montoire in France, where the tubes on his biggestever installation were pitting.  

I very reluctantly acceded to the opportunity of a olly – private aircraft to Brittany, good food, wine, seaside location and Duty Free on the way back. But it wasn’t how things turned out.  

When I was not at some sort of meeting, I was scrabbling around inside an evaporator, locating the places where the tubes had perforated. Wherever a crevice had formed between the stainless tubes and the supporting framework, corrosion was eating away at the metal. In that distant epoch, the French had yet to realise the restoring capabilities of tea and coffee breaks, so the formal meetings were one step from purgatory. All discussions had to be translated from one language to the other, mainly one way of course, where the operator and manufacturer sought, as well as a solution, to shift blame from themselves to the other party.  

How was it that pitting had never happened on any other of the Thurley installations? There had to be a change in design or operating procedures. It emerged that, at Montoire, the tube nests had been installed in concrete tanks, as there had been problems with the mild steel ones built earlier. The paint on these never stayed on and the tanks rusted away, giving a big maintenance headache, hence the switch to concrete.  

It was clear that nature, in allowing the paint to flake off, was telling us that she needed to get on with letting the mild steel tank do its job of protecting the tubing. But that mild steel could cathodically protect stainless steel was not then, forgive the pun, an idea that was current. My French opposite number opined that this was ‘bizarre’. My response – ‘Mais oui!Avez-vous une autre suggestion?’  

A Gallic sigh of exasperation indicated he could not come up with anything better. I recommended that mild steel strips be welded to the supporting framework. This cured the problem, but it was no victory over nature. It was, indeed, homage to her powers. Mild steel, in the spot-on terminology of corrosion engineers, was to act as a sacrificial anode.