Pressure maximum stress values

The formulas for thin-walled pressure vessels are first-order equations and are easier to rearrange and solve for minimum thickness and maximum stress values. The thick-walled vessel formulas provide the most accurate value for the stresses in the pressure vessel wall, but solving the thin-walled equations provides comparatively accurate results and is, therefore, quite useful for preliminary design estimates. 

In the case of the slip coefficient variation given in Figure 7, the pressure follows a sinusoidal curve with an average value equal to 5 MPa and average amplitude of around 0.55 MPa. The stress distribution around the caliper can be calculated with the Solidworks software, using the average value of pressure applied to the cahper. The maximum stress value obtained is equal to 196.2 MPa. 

The maximum allowable stress values at normal temperature range for the steel plates most commonly used in the fabrication of pressure vessels are given in Table 12-3. For stress values at higher temperatures and for other materials, the latest edition of the ASME Code should be referenced. 

The stress values in Table IX-1 and Table IX-4 are grouped by materials and product forms, and are for stated temperatures up to the limit provided in para. GR-2.1.2(a). Straight-line interpolation between temperatures is permissible. The temperature intended is the design temperature (see para. IP-2.1.4). Material performance factors located in Tables IX-5 are grouped by material type, material tensile or yield strength, and maximum system design pressure. Straight-line interpolation is permissible. 

It is crucial to define a reference configuration, or state, to which all tests can be reckoned. Such a reference state, referred to as hypertonic state, is defined as the state of maximum salinity of the extrafibrillar compartment then as the salt content overweights the presence of proteoglycans, the latter have a very small mechanical effect the hypertonic configuration is such that the stress is equal to the bath pressure. Therefore, stresses and pressures can be reckoned to their values at the hypertonic state from which all tests start and at which by convention the strain vanishes as well. 

Proof stress is the stress to cause a specified permanent extension, usually 0.1%. The maximum allowable stress specified by the ASME Boiler and Pressure Vessel (BPV) Code is calculated from these and other material properties at the design temperature, and allows for suitable safety factors. The basis for establishing maximum allowable stress values is discussed in Chapter 13 and is described in detail in the ASME BPV Code Section 11 Part D, Mandatory Appendix 1. 

UG-23 Maximum Allowable Stress Values UG-27 Thickness of Shells Under Internal Pressure UG-32 Formed Heads, Pressure on Concave Side UG-34 Unstayed Flat Heads and Covers... 

C = allowance for threading and grooving D = outside diameter of pipe P = internal pressure in psi S = maximum allowable stress value in psi T = wall thickness... 

For instance, for a 304 stainless steel welded seam pipe with an outside diameter of 3V2", to find the maximum internal pressure allowed for this pipe, use the pressure formula. Find what is called the stress value for a particular material (in this case 304 stainless steel) which is based on that material and the way it was fabricated - whether it is seamless, continuous welded, electric resistance welded, or electric fusion-arc welded. Most of the materials that you will run into will be ERW (electric resistance welded ) and thus have a seam, or will be seamless with no weld. The same material of a given diameter and thickness will be able to withstand higher internal pressure if it is seamless. 

There are other designations that should be considered for other types of service such as high pressure/high heat etc. These designations are encountered in tables used for calculating pressure allowable based on maximum allowable stress values (S-values). 

Note that the difference in pressure through the thickness of the body, giving rise to the stress, is usually much smaller than the value of the capillary pressure Pc at the critical point but there is a relation between them. The greater the capillary pressure, and the lower the permeability, the greater is the stress at the critical point. The maximum stress at the critical point approaches Pr when the evaporation rate is very high and cracking is most likely at the end of the CRP and the beginning of the FRPl. 

The ASME code (UG 99) requires a hydrostatic test of each pressure vessel to validate the design, materials, and construction before that vessel is put into service. The minimum value for the test pressure is 1.3 times the MAWP, corrected for the temperature at which the test is conducted. This temperature correction is the ratio of the stress value at the hydrostatic test temperature (usually room temperature) to the stress value of the material used in the design formulas, usually at the maximum allowable working temperature of the pressure vessel. To conduct the test, water is pumped into the vessel to increase the internal pressure to the level of the test value and then released. 

The results are shown in Table 24.6 where the maximum stress on the tube between the regenerative and the recuperative burner is almost the same for both tube inside pressures of 0-0.6 MPa. These values are thought to be low enough than the creep rupture strength at 900°C with a long working time—about... 

For the lower portion of tall towers, where the combined axial stress controls the design of the shell, there is the problem of selecting the maximum allowable axial compressive stress. The combined axial tensile stress presents no problem. The tensile stresses produced by internal pressure, bending stress of wind loads or bending stress firom seismic loads may be combined by simple addition of the stresses. The thickness of the shell may be calculated so that the combination of axial tensile stresses is equal or less than the maximum permissible value specified by the ASME Code. 

Because C, 0 are the functions of the water content ratio, is also related to the strata incidence and water content ratio. Before developing an oil reservoir, in-situ stresses should be obtained firstly. Using the in-situ stress values and strata incidence, the maximum pore pressure can be calculated through numerical simulation. In this way, reasonable water injection pressure values can be decided. 

The design requirements in ASME Section III limit the primary (pressure only) membrane stress to a value of about 13.8 MPa. As a result, the thickness of a PWR RPV is typically about 20-25 cm, while the wall of a BWR RPV is about 15 cm thick. Section VIII requirements limit the maximum stress to a lower allowable level which means that the RPV wall thickness must be greater to reduce the primary stresses. 

For class III surrounding rock, under the tail-race tunnel maximum pressure, the maximum tensile stress value is 0.55 MPa. The plain concrete lining is safe and reliable. 

---