Cockenzie steam drum

The Cockenzie steam drum failure of May 6 1966 [5] happened during the final, seventh cycle of hydraulic pressure testing before the steam drum would have been declared ready for service. It failed adjacent to one of the economizer nozzles, the transition pieces to the high-pressure pipes in operational service, would have led water from the underside of the drum to the boiler tubes (See Fig. 7.6.)... 

The Cockenzie steam drum after failure, with the failure site (inset). The dark tarnished area shows that the crack already existed during final heat-treatment, because the crack surface had discolored (public domain). 

The three steam drums were similar to the Cockenzie steam drum, although somewhat shorter. 

We all knew about the Cockenzie event - the whole electricity generating industry had learned a lot from it. Right now, we were raising the temperature and pressure in the steam drum to the highest it had ever experienced since commissioning and, furthermore, it was pressurized with steam. If it were ever going to fail, now was the time and if it failed, it was not hydraulic pressure, it was steam pressure, so it would blow us all away. 

The advantages of hydraulic proof pressure testing are best demonstrated by reference to the failure of a large steam separator drum at Cockenzie Power Station in East Lothian, Scotland, on May 6, 1966. (Separator drums are large, horizontal, cylindrical, thick-walled steel pressure vessels used to separate steam and water in coal-fired or nuclear power stations.)... 

If the Cockenzie drum had survived this hydraulic pressure test (the seventh and last) it would have entered service. Sometime later, when pressurized with steam, it would have failed, and the explosion would have caused massive damage, and probably injuries and deaths. The question is this How can we be really sure that there are no significant cracks in thick-walled pressure vessels ... 

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