Pressure retaining parts

ASTM A 990-05 Standard Specification for Castings, Iron-Nickel-Chromium and Nickel Alloys, Specially Controlled for Pressure Retaining Parts for Corrosive Service [currently contains CW-2M (C-4C) and two others]. 

To avoid brittle fracture during operation, maintenance, transportation, erection, and testing, good design practice shall be followed in the selection of fabrication methods, welding procedures, and materials for vendor furnished steel pressure retaining parts that may be subjected to temperature below the ductile-brittle transition point. 

Carbon and low alloy steel pressure retaining parts applied at a specified minimum design metal temperature (2.11.4.5) between -30°C (-20°F) and 40°C (100°F) shall require impact testing in accordance with 2.11.4.3.1 and 2.11.4.3.2. 

To be able to EC mark a product, the manufacturer must undergo, for each product and type of valve, a conformity assessment comprising the EC type or design examination and the assurance of the production quality system. The manufacturer must also demonstrate the quality compliances of all sub-suppliers and ensure that all critical parts (or at least pressure-retaining parts) are fully traceable and accompanied by a material certificate. Procedures to certify conformity to PED are carried out by a notified body approved by the member states of the European Community. With completion of the assessment, the manufacturer may stamp the EC mark on the product. 

About the materials, PED defines the pressure-retaining parts for the valves in the technical file of each valve type. Typically, for an SRV, this would be body, bonnet, disc and nozzle but could be different depending on the type of SRV. These parts must satisfy material requirements and have an EN10204 3.IB (now 3.1) material certificate, and are therefore traceable. 

While most manufacturers provide a 3.1 (EN 10204) material certificate for traceability per PED on the body, bonnet, nozzle and disc only as being the pressure retaining parts, one could argue that this should be extended to all parts which truly contain the pressure, including bolts, studs and nuts. The code is not explicit on the matter and it is up to the user to evaluate the issue. 

Pressure retaining parts of components in the reactor coolant system Components of or connected to the primary reactor coolant system that are essential for ensuring the shutdown of the reactor and cooling of the nuclear fuel in relevant operational states and in postulated accident conditions ... 

Cast iron pressure-retaining parts should not be used in process fluid serviees, but may be used in fresh cooling water services for heat exchanger ehannels and cover sections. 

A damping value of 5 percent shall be used for new analyses for non-pressure retaining parts of equipment, such as motor control centers, cabinets, panels, racks, fans and transformers, etc. See IEEE-344-75 and "Restart Criteria for Seismic Qualification", a memorandum from Patterson to Peckinpaugh, dated November 1988). Higher damping values may be used for special designs when justified. 

For the non pressure retaining parts including valve yokes, connecting bolts for valves and pumps, and equipment supports, use the allowable stress limits (including buckling requirements) In AiSC Code 7th edition (1973) with an Increase of 1/3 (Section 1.5.6 of NUREG-0800, Rev. 1) for the DBE. Alternatively, the 8th Edition of the AISC Code,... 

Providing the pressure retaining parts of the RCS whose failure could cause a loss of coolant accident in excess of the normal make-up capability for the reactor coolant ... 

Rupture Disks A rupture disk is a device designed to function by the bursting of a pressure-retaining disk (Fig. 26-15). This assembly consists of a thin, circular membrane usually made of metal, plastic, or graphite that is firmly clamped in a disk holder. When the process reaches the bursting pressure of the disk, the disk ruptures and releases the pressure. Rupture disks can be installed alone or in combination with other types of devices. Once blown, rupture disks do not reseat thus, the entire contents of the upstream process equipment will be vented. Rupture disks are commonly used in series (upstream) with a relief valve to prevent corrosive fluids from contacting the metal parts of the valve. In addition, this combination is a reclosing system. 

Body A pressure-retaining or -containing member of an SRV that supports the parts of the valve assembly and has provision(s) for connecting to the primary and/or secondary pressure source... 

Pressure-containing parts - Those valve parts whose failure to function as intended would result in a release of retained fluid to the atmosphere. 

To the extent practicable, the pressure retaining components shonld be visually examined while the system is operating under the test pressnre and temperature conditions. The test pressure and temperature should be maintained for a sufficient period before the examination to ensure that all possible leakages can be identified. The accessibility of components to be visually examined should be considered (for example, with regard to the possible need for removal of insulation). Acoustic emission methods may be used as part of such inspections. 

Microscopic vapor nuclei in the form of bubbles entrapped on the heat-transfer surface must exist in order for nucleate boiling to occur. Surface tension at the vapor-liquid interface of the bubbles exerts a pressure above that of the liquid. This excess pressure requires that the liquid be superheated in order for the bubble to exist and grow. The porous surface substantially reduces the superheat required to generate vapor. The entrances to the many nucleation sites are restricted in order to retain part of the vapor in the form of a bubble and to prevent flooding of the site when liquid replaces the escaping bubble. 

The prestressed concrete vessel has a cavity with a diameter of about 12 and a depth of about 38 m, containing some 3,300 m of water. The concrete vessel is a monolith with a cross-section of about 27 and a height of about 43 m. It is anchored to the foundation mat structure by means of prestressing tendons. The pressure retaining capability of the vessel is ensured by a large number of prestressing tendons - partly horizontal tendons run around the cavity, partly vertical tendons run from the top to the bottom, - and by reinforcement bars. 

The containment vessel provides a low leakage, pressure retaining boundary which completely surrounds the primary system boundary. The containment includes a containment vessel (lower part) (to contain leaks from the reactor vessel) and a containment dome (upper part), which is to mitigate the releases due to postulated severe accidents. The upper and lower parts of the containment are connected to each other by a containment ring located at the same elevation as the top of the reactor head. 

The RCS forms a pressure retaining boundary for the reactor coolant and is therefore a barrier to radioactive releases in all modes of plant operation. The RCS transports the coolant and thereby heat from the reactor core either to the steam generating systems or directly to the turbine generator. The RCS also forms part of the route for the transport of heat from the reactor core to the ultimate heat sink during shutdown and in all transient conditions that are considered in the design of the RCS. 

Characteristic of fluidized bed reactors is the large wind box to equalize pressure. This is a primary requirement to get even flow through the bed. The expanding shell at the upper part is there to retain as much solid as possible in the reactor. 

To conclude this section let us note that already, with this very simple model, we find a variety of behaviors. There is a clear effect of the asymmetry of the ions. We have obtained a simple description of the role of the major constituents of the phenomena—coulombic interaction, ideal entropy, and specific interaction. In the Lie group invariant (78) Coulombic attraction leads to the term -cr /2. Ideal entropy yields a contribution proportional to the kinetic pressure 2 g +g ) and the specific part yields a contribution which retains the bilinear form a g +a g g + a g. At high charge densities the asymptotic behavior is determined by the opposition of the coulombic and specific non-coulombic contributions. At low charge densities the entropic contribution is important and, in the case of a totally symmetric electrolyte, the effect of the specific non-coulombic interaction is cancelled so that the behavior of the system is determined by coulombic and entropic contributions. 

Pave = average total pressure in tower, atmospheres Hl = height of liquid film transfer unit, ft Hg = height of gas film transfer unit, ft a = effective interfacial area for contacting gas and liquid phases, ft /ft. Because this is very difficult to evaluate, it is usually retained as a part of the coefficient such as Kca, Ki a, kca, and k.La. 

A bifurcation cascade with micro channels feeds a wide fixed bed (channel void space for particle insertion), followed by a multitude of catalyst retainers, which act like frits, i.e. support the catalyst particles and prevent their loss [7, 77, 78]. Besides supporting the particles, these parts have a size-exclusion function to the lower size limit of about 35-40 pm. The retainers are followed by an array of elongated channels that serve to build up a uniform pressure drop along the wide retainer bed. Finally, the streams are collected in a bifurcation cascade of identical shape as the feeding cascade, but mirror-imaged in position. 

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