Piping design safety

Any process heat plant design implies piping through the containment to connect the reactor vessel with the chemical plant. The fracture of a pipe could result in the accumulation of a flammable gas mixture in the containment. Precautions must be taken to minimize the risk of a fire or gas explosion such as avoidance of explosive gas ingress, proper detection devices, inerting, sufficient safety distances, appropriate layout of secondary coolant boundary, explosion-proofed wall, plant isolation valve. For the PNP-500, the use of two concentric pipes for the process gas carrying lines were recommended. Alternatives are concrete channels around the gas lines or inerting of the containment [10]. 

A design safety factor S allows for unexpected variations in the pipe properties or dimensions, or defects caused during installation. The design hoop stress o-qh is given by... 

Decision criteria relates to the safety critical deterioration level. It is necessary to determine this level to be able to make appropriate decisions regarding further action. Usually a first basic intervention level is defined according to relevant codes, standards or internal company requirements. A minimum required wall thickness is usually determined due to a stress criterion and depends on allowable stress, design pressure, pipe dimensions and material strength. When deterioration beyond this basic intervention level is revealed through inspection, further actions must he decided. When the basic intervention level is reached, there may... 

One would expect that an experienced supplier of pneumatic conveying equipment would have more experience-based knowledge on which to design the pipe supports, but that expectation has on occasion proved to be over-optimistic. A prudent engineer would do well to take the highest of any of the values calculated above or stated by the supplier, and allow a safety factor of at least 3.0 to allow for dynamic magnification of the load. 

HAZOP is the most widely used technique by ICI developed several decades ago and involves vessel-to-vessel and pipe-to-pipe review. The entire flow sheet is systematically reviewed by design, safety, and process engineers using a set of guidewords to identify... 

Thus, design values are based on the strain-to-first-crack or the empirical weep point. For normal design conditions a strain of 0.0018 in./in. is used, which provides a five-to-one safety factor. For transient design conditions a strain of 0.0030 in./in. is used, for a safety factor of approximately three to one. To those familiar with the design safety factors of other pipe manufacturers following NBS Voluntary Product Standard PS 15-69, these safety factors may seem modest. However, PS 15-69 is based on the ultimate tensile strength of the material. 

The final step in the plot plan arrangement is to space equipment and supporting facilities for operator and maintenance access, safety, piping flexibility and support, and platforming requirements. At this stage, the layout designer must rely on experience because the final information is not available for calculating... 

The OASIS code has been used for the thermal hydraulics analyses. A large number of events were analysed. The objective of these studies was to identify the worst-case scenario. Therefore, rupture position, rupture time, and break size spectra must be analysed. Currently, the detailed thermal hydraulics analysis for the primary coolant pipe break accident as a function of the break position is being performed. This study is based on conservative assumptions, as required for Category 4 DBE analyses. The main results of this analysis are the core inlet and outlet temperatures, the break flow rate, the IHX inlet and outlet temperatures, as well as the and clad temperature distribution. The results of the calculations show that the hotspot temperatures for the cladding and for the coolant are below the design safety limits (DSL). These temperatures are lower than the sodium boiling temperature. The regulator accepted the methods applied, as well as the results of the analysis. 

The scope of the directive covers the design, manufacture and conformity assessment of pressure equipment and assemblies with a maximum allowable pressure greater than 0,5 bar. A pressure equipment in the sense of the directive is any vessel, piping, safety accessory or pressure accessory. An assembly means several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and functional whole. It is important to be aware that the directive relates exclusively to the pressure risk and that therefore other directives, such as for machinery, low voltage may be applicable to the equipment concerned. 

The introdrrction to the code sets forth engineering reqrrirements deemed necessary for the safe design and constrrrction of piping systems. While safety is the basic consideration of the code, this factor alone will not necessarily govern final specifications for any pressrrre piping system. 

Safety Considerations Design and location of storage tanks, vents, piping, and connections are specified by state fire marshals, underwriters codes, and local ordinances. In NFPA 30, Flammable and Combustible Liquids Code, 1993 (published by the National Fire Protection Association, Quincy, Mass.), liquid petroleum fuels are classified as follows for safety in handhng ... 

The maximum pressure from an explosion of a hydrocarbon and air is 7 x initial pressure, unless it occurs in a long pipe where a standing wave can be set up. It may be cheaper to design some small vessels to withstand an explosion than to provide a safety relief system. It is typical to specify %" as minimum plate thickness (for carbon steel only). 

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