Piping accident contribution

Isolation - It has been shown that the addition of isolation valves at periodic intervals is not as cost effective as prevention measures such as thickness inspections or tests. However all pipelines should be provided with a means for emergency isolation at it entry or exit from a facility. Offshore facilities may be particularly vulnerable to pipeline incidents as the Piper Alpha disaster has shown. In that accident a contributing factor to the destruction was the backfeed of the contents of the gas pipeline to platform once the topside isolation valve or piping lost its integrity. Further isolation means (i.e., a subsea isolation valve SSIV) were not available. 

Other causes that contributed to the accident include (i) lack of slip-blind plates that would have prevented water from pipes entering into the MIC tanks via faulty valves, and (ii) use of carbon-steel valves, despite the fact that they corrode when exposed to acid (the leaking carbon-steel valve that allowed water to enter the MIC tanks was not earlier repaired as this was too expensive). 

RHR suction line is used as SIS hot leg injection. This approach is made possible because SIS hot injection is manually actuated after 90 minutes in case of a loss of coolant accident to avoid boron crystallization. With such a design, a big pipe and its associated valves together with the injection nozzle could be deleted. This contributes to a certain gain in safety (reduction of the number of nozzles on the primary coolant lines) and in investment costs. 

Plastic pipe extruded by Century Utility Products, Inc., and made from Union Carbide s DHDA 2077 Tan resin has poor resistance to brittle-hke cracking under stress intensification, and this characteristic contributed to the Waterloo, Iowa, accident. 

Example We will illustrate this approach with an accident during construction of a pressure tunnel to a hydroelectric power plant. While transporting a 12-ton pressure pipe in the tunnel, the operators lost control of the pipe. It skidded several hundred metres down the tunnel and caused substantial equipment damage. Figure 6.5 illustrates the different deviations and contributing factors. 

Figure 6.5 Deviations and contributing factors of an accident during transportation of a 12-ton pressure pipe in a tunnel.

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