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A naphtha hydrotreater (NHT) feed/effluent exchanger train comprised 2 parallel banks of 3 stacked shells in series. One of the two banks was being placed back in service after off-line cleaning and inspection. The procedure for this ‘restreaming’ operation includes gradual and concurrent operation of several large isolation valves, requiring the help of several operations personnel. While the restreaming operation was taking place, the carbon steel (CS) shell of the middle exchangers of the adjacent ‘in-service’ bank of 3 exchangers ruptured catastrophically along the seam welds of the shell. The rupture caused a massive release of hot hydrogen and naphtha which auto-ignited and exploded. Seven employees working in the immediate vicinity of the exchangers were fatally injured.
Ask yourself and your crew:
- How can something like this happen here (e.g. on our site)?
- What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
- How do we know the risk controls/barriers are working?
- What improvements or changes should we make to the procedures, controls/barriers or the way we work?
Original content courtesy of IChemE Safety Centre
