HOSPITALS IN A MARINE ENVIRONMENT
He said: “These are the main forms of protection, but as to some of the more basic things to consider, we need to prioritise effective drainage – so we are not trapping moisture in a pool that is going to grow, avoid capillary action, and, wherever possible install plant or equipment inside the building.” He added: “I know that might sound pretty obvious, but if you look at air-handling units, we regularly end up installing ventilation plant outside, much to nearly every engineer’s dismay. The answer is to put some form of roofing and protection around it.”
Examples of ‘common mistakes’ Before closing his presentation, James Tinsdeall said he would highlight a few examples of ‘common mistakes’ in terms of maintaining buildings in a marine environment, which he did using slides. His first slide showed 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. He said: “There is also no protection on the inside from any moisture, whether from condensation, or from salt within the marine environment.” His next showed a small access door on a piece of ventilation trunking running over a roof serving an X-ray department. He explained: “The door is galvanised steel, the cladding above it is aluminium, and the little latch is galvanised steel as well. The rivet in the middle, however, is made of Monel. Monel is probably as far up the galvanic table as you can get, and thus at the very opposite end of the table.” The corrosion evident in the picture had, he explained, taken hold in just two months. He said: “Having recognised the problem, we are going to replace the rivets and not use Monel rivets in such applications in the future.” Moving to his next slide, James Tinsdeall said: “The last slide I showed you
‘How did we end up here?’ Answering his own question, he said: “I don’t know whether – when we go to the design of products, anybody actually stops and says to the manufacturer before they produce components: ‘This is where we are located, two miles away from breaking surf in a marine environment’.” He acknowledged that many building material manufacturers were ‘operating in a highly competitive market’. He said: “Everything they do is tendered one way or another, and of course the main contractors are trying to beat down the sub-contractors on cost.”
A ventilation heater battery, where the finning at the top is copper, and the base galvanised steel. There is ‘a moisture trap’ at the bottom.
was of dissimilar metal components at the West Cornwall Hospital in Penzance, probably the site where we have the most issues with marine and salt-related corrosion. In this next one you can see a ventilation heater battery, where the finning at the top is copper, while the base is galvanised steel. There is a moisture trap at the bottom, so any moisture that runs down is effectively a frost factory.
Moisture containing salt “Moisture containing salt – a very good electrolyte – is trapped between the copper and the galvanised steel, and corrosion slowly eats away, dissolving the galvanised steel, and then moving its way to the steel. The copper is higher up the galvanic table, whereas the zinc is down the bottom and is sacrificed very quickly.” The next slide showed the effects of galvanic corrosion on an electroplated bolt in 316 stainless steel after four years. James Tinsdeall said: “Although the bolt is coated in 316 stainless steel, there is also a nickel-plated screw. The ‘dip’ allows moisture to fall in there, at which point there is a reaction between the stainless steel, the nickel, and the steel as well.” Another slide showed the same heater frost battery shown a few slides earlier, with its copper finning. James Tinsdeall said: “We pulled away the finning to assess its condition, and where the copper finning goes around the copper tube, it will allow in moisture. Due to the temperatures in Cornwall we very rarely actually use the frost batteries, so they will sit there cool and damp, and of course that aids corrosion too.”
The heater frost battery shown a few slides earlier, with the effects of internal corrosion clearly evident.
46 Health Estate Journal January 2019
How did we end up here? The speaker then asked rhetorically – alluding to the various problems and potential issues with galvanic corrosion –
Neither were long-term corrosion warranties ‘commonplace’. He said: “We’re trying to push this, and test the boundaries of it. For instance, we have a new-build coming up which is an immunosuppressed ward, with about 10 air-handlers on it, and we are trying to push the manufacturer to see what we can achieve warranty-wise. When you stop and look at it, the devil is in the detail, and, for instance, you are never going to get an M&E design consultant writing in the detail to ensure, for instance, that crevices are electrically isolated. They are more interested in how many cubic metres of air an air-handling unit is going to handle, and at what temperatures.”
Lessons from the car industry James Tinsdeall said there were some potential lessons in the field to learn from the automotive industry. He said: “I showed you a picture earlier of one of my previous cars, a 1980s Alfa Romeo, which had suffered serious corrosion. However, the car manufacturers overcame such issues without resorting to gold plating or stainless steel. The only manufacturer I remember using stainless steel was De Lorean. The automotive engineers changed the design of the crevices, modifying the wheel arches and doors so that there was nowhere for the water to sit and get trapped. They also improved the cavity drainage, so that there are now drainage points on the sills and the other elements of the car so that any water that gets in doesn’t get trapped, and instead simply drains out. “The car industry also improved the quality of the steel, and enhanced cars’ protective coating using some galvanising and electroplating. Car manufacturers also tend now to dip the whole frame of a new vehicle into the paint, rather than trying to just spray it on from the outside. The key thing with this for our profession is that if we look at a typical hospital ventilation unit, it is normally made from galvanised steel and then drilled, machined, and assembled, and not dealt with afterwards. It is the final detail that really needs looking at here.” This closed James Tinsdeall’s very interesting and insightful presentation.
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James Tinsdeall
James Tinsdeall
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