Piping design failure

Fatigue Failure - The combined discharge header system should be designed in accordance with the same considerations of potential piping fatigue failure as described below for closed discharge systems. 

But, all of these obvious technical pipeline considerations are sometimes overh>oked, and many of the most infamous incidents have involved poor practices in piping design, in operations, or in piping maintenance systems. The American Insurance Association states Piping hazards are often underrated as compared to pressure vessels although the history of failures does not warrant this... . Piping systems should be located in. serviceable areas. They should be constructed in accordance with appropriate code requirements and inspected by appropriate means.. .. [20]... 

Although worldwide production of heat pipes designed for applications involving the thermal control of electronic components or devices was in excess of 1,000,000 per year in 1992, it is difficult to calculate a mean time to failure (MTTF) for heat pipes, thermosyphons, and other similar devices due to the relatively small amount of data that exists on actual products in operation. Experience with a wide variety of applications ranging from consumer electronics to industrial equipment has demonstrated that mechanical cleaning of the case and wick-... 

Grades of PE have been specially developed for the gas pressure pipe market. Eirst-generation HDPEs were not used in the UK. The second generation of MDPE copolymers has superior creep rupture resistance at the pipe design lifetime of 50 years (Fig. 14.5). The data falls on one or more lines lines of shallow slope are associated with ductile failure and lines of steeper slope with brittle plane strain crack growth (Fig. 14.3). The... 

Ultrasonic monitoring shows thin walls for pipes, internals or vessels faulty ultrasonic instrument/[corrosion] /faulty design. Failure of supports, internals, vessels" [corrosion] /faulty design/unexpected stress or load. 

In the design and evaluation of nuclear power plants, internally generated missiles arising from PIEs (such as the failure of pressure vessels and pipes, the failure of valves, the ejection of a control rod and the failure of high speed rotating equipment) should be considered. The potential for secondary missiles should also be evaluated. Measures to prevent the initiation of internally generated missiles should be undertaken if such measures are practicable. 

A more subtle effect of fluids coming into contact with polymers for long periods is ESC [1]. This occurs when a contacting fluid causes the rapid acceleration of slow crack growth in stressed areas. This effect is very important for pressure pipe designers since their pipes are continuously stressed. ESC can lead to brittle failure ahead of anticipated long term ductile bursting. 

RTR pipe designers also use a stress-strain curve similar to that used by steel pipe designers. However, instead of a yield point, they use what is called an empirical weep point, or the point of first crack (see Fig. 5-30). It is determined by either coupon or hydrostatic tests. The weep point is the point at which the matrix becomes excessively strained so that minute fractures begin to appear in the structural wall. At this point it is probable that in time even a more elastic liner will be damaged and allow water or whatever else the pipe is carrying to ooze or weep through the wall. As is the case with the yield point of steep pipe, reaching the weep point is not necessarily cataclysmic. The pipe can still continue to withstand quite a bit of additional load before it reaches the point of ultimate strain and failure. 

High design-pressure steam generator system No SG safety valves Primary system cannot over-pressure secondary system Feed/steam system piping designed for full RCS pressure reduces piping failure probability -Steam generator tube rupture -Steam line break -Feed line break... 

We conclude therefore that unless cryogenic pipelines are properly designed for the condition of bowing as well as uniform thermal cool-down, intolerable pipe displacements, severe pipe stresses, and pipe support failures will undoubtedly occur. 

Deflagration Arresters The two types of deflagration arrester normally considered are the end-of-line arrester (Figs. 26-23 and 26-24) and the tank vent deflagration arrester Neither type of arrester is designed to stop detonations. If mounted sufficiently far from the atmospheric outlet of a piping system, which constitutes the unpro-tec tea side of the arrester, the flame can accelerate sufficiently to cause these arresters to fail. Failure can occur at high flame speeds even without a run-up to detonation. 

Check valves are required in the piping system at any point where backflow of gas after a shutdown has the ability to restart the compressor, running it backwards or, for that matter, even in the normal direction. Reverse rotation is totally bad, as many components of the various compressor types are not designed for reverse rotation, and there is some possibility, generally remote, that the compressor could reach a destructive over speed. Forward rotation is bad primarily because the intent was to stop the compressor, and it is now operating out of control. This is a problem, particularly if the shutdown was caused by a compressor failure indication, and the need to stop was to prevent further damage. In this mode, it is unlikely that the compressor can attain an overspeed condition. An application with a high potential for backflow is the parallel operation of two or more compressors. 

LOCA, is presented in Table 3.4.5-1. In preparing the event tree, reference to the reactor s design determines the effect of the failure of the various systems. Following the pipe break, the system should scram (Figure 3.4.5-2, node 1). If scram is successful, the line following the node goes up. Successful initial steam condensation (node 2 up) protects the containment from initial overpressure. Continuing success in these events traverses the upper line of the event tree to state 1 core cooled. Any failures cause a traversal of other paths in the evL-nl tree. 

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