Phosphate Rocks Chapter 34: Vessel Entry

The new ammonia pipeline bucked and squirmed so violently that the whole pipe bridge jumped and twisted as the series of shocks shuddered away from the point where the liquid ammonia was introduced, towards the spheres. 

Visibly shaken, the trio of engineers abandoned the task, closed the ammonia valves and replaced the padlocks before scuttling off to the office to discuss what had gone wrong. 

They soon reached the conclusion that the new pipeline had not been properly drained after the hydrotest. As the liquid ammonia flashed down to atmospheric pressure and minus thirty-three degrees centigrade in the almost-empty pipeline, the residual water must have been simultaneously frozen into ice bullets and propelled by the flashing gas at supersonic speed. 

Bullets don’t take corners too well. 

In conclusion, it was entirely John’s fault; he should have drained the line properly. 

They did not consider the impossibility of the task. 

Tall Willy insisted on a thorough examination of all equipment potentially impacted by flying ice bullets. The pipe bridge was inspected: a few loose bolts had to be tightened, and the warped or cracked struts replaced. 

The new pipe was checked with an ultrasonic probe, with particular attention to the bends. The wall thickness appeared unchanged. A lot of noise but no harm done. But the sphere was too thickly insulated for an external inspection; a vessel entry was required. 

As punishment for his earlier misdemeanours, John was charged with getting the sphere ready and organising the physical disconnection from all live pipework. 

The original storage installation was well constructed. An ICI design guide had been put together by an engineer who had operated and maintained plants at Billingham and Severnside. If a complex vessel must be inspected regularly, your design has to make it easy to do it right. 

Each pipeline had a short spool – a removable section of pipe – between the last valve on the pipeline and the point where it entered the sphere. After those nearest valves were closed and locked, the sphere was pumped empty. 

Production continued, using ammonia from the other two spheres, and the common pipelines remained full of ammonia under pressure. Bob, the fitter, was tasked with removing the spools between each live pipeline and the empty sphere. Fitting a blank, a thick metal disc bolted to the downstream side of the valve, would ensure no ammonia accidentally entered the sphere through a leaking valve. 

The high pressure pipelines were fitted with a double block and bleed: two valves with a small test valve in-between. 

Bob was working on the new pipe when a strange thing happened. The two valves at the end of a pipe full of ammonia were closed. When he opened the bleed valve in-between them, it proved that the upstream valve was holding, and it was safe to remove the spool. But when he started to disconnect the spool, ammonia began to pour out of the closed valve. Bob donned his breathing set, tightened the spool back up and moved away. 

He needed a water hose to clean up the area. John was a tidy man and made sure hoses were not left lying around the site. This was annoying for the fitters and operators as they regularly needed to wash away small spills or add water to a phosphoric acid reactor when filtration was poor, so most crews had a secret stash of such things. 

Alternatively, Becksy could be relied upon to find whatever was needed, bypassing the stores and the rigorous inspection process implemented by Tall Willy. 

The hose stash was empty and Becksy could not be found, so Bob had to call John. Together they carried a long water hose from the store and connected it to the nearest tap. 

In mistake number seven, Keith, the design engineer, had removed a water line and hose points when he redesigned the ammonia piping, so they had to run the hose up and over the pipe bridge to avoid laying it across the roadway. John inhaled deeply as Bob washed away the ammonia spill. 

John asked Bob what had happened, and when Bob explained, John didn’t believe him. Show me, he said. 

John stood back while Bob put on his breathing apparatus. Dressed like a scuba diver in a green PVC suit with a face mask and oxygen cylinder, Bob opened the bleed valve again to show John there was no leak. 

But the moment Bob loosened a bolt between the open spool and closed valve, liquid ammonia poured out. Exactly as before. 

John scratched his head as he washed the spill away. Removing an empty, open piece of pipe couldn’t possibly create a leak. 

John called Roderick, the maintenance manager. He didn’t believe it either. They showed him and then washed away the evidence. 

Roderick called Tall Willy, the chief engineer. The pantomime was repeated but this time the valve handle also fell off. 

The operation was halted.