Phosphate Rocks Chapter 18: Inflatable Boat

The ammonia storage spheres were made of metal, multiple plates of special steel welded together. Keeping the ammonia inside its metal shell required constant vigilance. And maintenance. 

Tall Willy, the engineer who moved to Leith from Aberdeen, was more used to wood than steel. So ICI sent him on courses, and he did his own reading. His chief concern became stress corrosion cracking. A combination of chlorides from the sea and the ever-cycling internal pressure, rising during the day and falling at night, made the steel of the spheres the perfect target for this slow and insidious form of rot. Unlike rust, another form of corrosion, it was impossible to detect without close inspection of the inside surface. 

It’s easy to test for stress corrosion cracking in a laboratory. You take a sample, slice though the metal and look for cracks under the microscope. That is called destructive testing. Non-destructive testing (where you leave the structure intact) is harder. Tall Willy had settled on dye penetration testing, starting with the places where the residual fabrication stress was highest: on welds, around manholes and nozzles – the points where pipes enter and leave. 

First you paint the surface with a pink dye. Bright girly pink. Then you spray a white powder over it. If the metal below is smooth, it looks like fresh snow. Where there are cracks or imperfections, the pink dye bleeds through. 

The problem was the access. Or rather the cost of access. Or more accurately, the lack of provision in the maintenance budget by Willy’s predecessor for the cost of access. Tall Willy had to find savings every year even as the demands of the ageing plant increased. The cost of scaffolding inside one of the spheres to allow him to reach every square centimetre of the interior was tens of thousands of pounds. The recommended regime for internal inspection every three years meant budgeting to inspect one of the three spheres every year. 

Tall Willy knew that if he went to the company technical safety committee, they would support him. The problem was that Billingham had excess capacity and this would be the perfect excuse to shut down the ammonia storage at Leith. And everything it fed. Nitric acid. Ammonium nitrate. Granulation. Jobs. The second of a thousand cuts. 

Tall Willy was out fishing when the idea came to him. It was a perfect day. Cold and wet meant quiet. Only the gentle wind in the trees and the soft rain falling into the tumbling river disturbed the silence. He was casting from the riverbank, idly watching a tangle of red-gold leaves and twigs caught up in a fallen tree. It was raining on the hills and the river was in spate. As he watched the level of the water rise, the branch wedged between the riverbed and the bank barely moved, but the floating autumn raft of debris rose higher and higher until it cleared the obstruction and sailed off down the river.  

Willy bought an inflatable boat for £20. He filled the empty, clean sphere with water. An Olympic swimming pool-worth of water. He threw the boat in and inflated it through the manhole. Then he climbed down a rope ladder and paddled round the inside of the sphere.  

When he was ready to descend, he sounded a foghorn and his assistant opened the drain valve to let some water out: fifty bathtubs-worth for every metre of descent by the time he was halfway down.  

Whenever he found a pink imperfection, he sounded the foghorn twice and marked it with a permanent, waterproof marker. By the time he was at the bottom, he had marked out seven repairs and his assistant outside had noted the exact height of each one, based on the volume of water discharged from the sphere through a totalising flowmeter. Willy didn’t attempt any hot work from his boat. Simple platforms were erected to reach the seven repairs, the defects were ground out, welded, stress-relieved and tested again. 

Water played an important part in other ways. Willy was able to confirm the theory that adding a tiny amount of water to the ammonia significantly reduced the appearance of stress corrosion cracking. Inspections were gradually extended to every six years, and Willy’s boat was not required as often. 

His initiative was copied throughout the company, saving millions, and Tall Willy was promoted to chief engineer. He saved enough on his maintenance budget to buy a proper, clean lockable shed for lubricants, just like the one he had insisted on at Stinky Miller’s, and attached the new keys to the old Aberdeen key fob. The number of breakdowns on the site fell dramatically.