HOSPITALS IN A MARINE ENVIRONMENT
Seagulls have proven ‘quite an issue’ for the Trust; they are a protected species. They also seem equally happy to nest on both shallow and pitched roofs.
engineer. He said: “When the engineer – quite a sizeable and strong-looking man in fact – arrived and realised he might be confronting herring gulls, he refused to go up on the roof, so we had to send up three of our Estates team up with sticks to scare off the gulls before he would go up and undertake the necessary repairs. Herring gulls will fly very close to people, and seem equally happy to nest on both shallow and pitched roofs.”
Deterrents tried
Among the methods that the Trust’s Estates team has tried to deter the gulls from nesting has been to scare them. James Tinsdeall elaborated: “We have used birds of prey to do this, and with a licensed contractor we can also swap the gulls’ eggs for dummy eggs. However, both the scaring of these large birds and the swapping of their eggs will take 2-3 years to bring the population down. We have also used distress call sounders, but these just gave everybody on site a headache. We also experimented with plastic owls and hawks, but these simply gave the gulls somewhere else to sit.” The speaker said he would now move on to talk about a marine environment- related problem that he believed the audience would have certainly anticipated him discussing – metal corrosion. He said: “There are several main types of metal corrosion, starting with atmospheric,
which is where, for example, you have some exposed steel and it corrodes at a certain rate, relatively slowly, and fairly predictably. You then get into what I would refer to as ‘crevice’ corrosion – where you have two bits of metal close together and moisture gets trapped. Next, you have galvanic corrosion, where you have dissimilar metals, which can cause quite significant problems. Finally, you have pitting, where there local degradation to the surface finish sees the pitting works its way all the way through the metal.”
Galvanic corrosion
Focusing on galvanic corrosion in particular, with a slide of a galvanic table, James Tinsdeall explained that among the more resistant metals to this form of corrosion was Monel, a group of nickel alloys, primarily composed of nickel and copper, with small amounts of iron, manganese, carbon, and silicon, copper, zinc, stainless steel, and standard steel. He elaborated: “In essence, the metals at the top of the galvanic table like gold are the most resilient to corrosion, and those such as magnesium the most easily corroded. These are the most anodic and will dissolve via galvanic corrosion. The further apart in the table they are, the quicker galvanic corrosion involving two dissimilar metals will occur.”
The effects of galvanic corrosion on an electroplated bolt in 316 stainless steel after four years.
He went on to explain that in selecting materials for buildings and plant, it was vital to look at ‘how long we are designing for’. He said: “The magic answer would be to make everything out of very expensive material and then buildings would theoretically last forever. The reality, though, is that we are designing for a specific time period, and we need to think about its duration so we can make the most sensible decision.
Slowing down the process “If we have dissimilar metals in an item of equipment or plant,” he continued, “and they are electrically separated with a plastic insulator, that will slow down corrosion, because the galvanic element will be missing. We can also electroplate things, and here we tend to use the more ‘noble’ metals. Standard steel is the usual one. Because we are putting nickel plating on an item, for example, while the nickel is intact and untarnished it will resist corrosion extremely well. Damage it, though, and expose the steel, and the two elements will start to react; the steel will rot at a very rapid rate.
A ‘sacrificial’ layer
An example of poor drainage, combined with use of dissimilar metals – including galvanised steel with a plain steel bolt going through it, and failing of the powder coating.
“Galvanising works the other way – the zinc on the exterior will corrode quite quickly; it is there as a sacrificial layer. Scratch the item and you will get some rust, but it won’t increase the rate of corrosion.” Other protective options against rust, Jim Tinsdeall explained, included cathodic protection using a DC current, and paint and powder coatings.
January 2019 Health Estate Journal 45
James Tinsdeall
James Tinsdeall
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