DIN EN 12516-2
Industrial valves - Shell design strength - Part 2: Calculation method for steel valve shells; German version EN 12516-2:2014
Industriearmaturen - Gehäusefestigkeit - Teil 2: Berechnungsverfahren für drucktragende Gehäuse von Armaturen aus Stahl; Deutsche Fassung EN 12516-2:2014
This European Standard specifies the method for the strength calculation of the shell with respect to internal pressure of the valve. EN 12516 "Industrial valves - Shell design strength", is composed of four parts. EN 12516-1 and EN 12416-2 specify methods for determining the thickness of steel valve shells by tabulation and calculation methods respectively. EN 12416-3 establishes an experimental method for assessing the strength of valve shells in steel, cast iron and copper alloy by applying an elevated hydrostatic pressure at ambient temperature. EN 12416-4 specifies methods for calculating the thickness for valve shells in metallic materials other than steel. The calculation method in accordance with EN 12416-2 is similar in approach to DIN 3840 where the designer is required to calculate the wall thickness for each point on the pressure temperature curve using the allowable stress at that temperature for the material he has chosen. The allowable stress is calculated from the material properties using safety factors that are defined in EN 12416-2. The formulae in EN 12416-2 consider the valve as a pressure vessel and ensure that there will be no excessive deformation or plastic instability. The tabulation method in accordance with EN 12416-1 is similar in approach to ASME B 16.34 in that the designer can look up the required minimum wall thickness dimension of the valve body from a table. The internal diameter of the inlet bore of the valve gives the reference dimension from which the tabulated wall thickness of the body is calculated. The tabulated thicknesses in accordance with EN 12416-1 are calculated using the thin cylinder formula that is also used in EN 12416-2. The allowable stress used in the formula is equal to 120,7 N/mm2 and the operating pressure, pc, in N/mm2, varies for each PN and Class designation. EN 12416-1 gives these pc values for all the tabulated PN and Class designations. EN 12416-1 specifies PN, Standard Class and Special Class pressure temperature ratings for valve shells with bodies having the tabulated thickness. These tabulated pressure temperature ratings are applicable to a group of materials and are calculated using a selected stress which is determined from the material properties representative of the group, using safety factors defined in EN 12416-1. Each tabulated pressure temperature rating is given a reference pressure designation to identify it. The tabulation method gives one thickness for the body for each PN or Class designation depending only on the inside diameter, Di, of the body at the point where the thickness is to be determined. The calculated pressure is limited by the ceiling pressure which sets up an upper boundary for high strength materials and limits the deflection. A merit of the tabulation method, which has a fixed set of shell dimensions irrespective of the material of the shell, is that it is possible to have common patterns and forging dies. The allowable pressure temperature rating for each material group varies proportionally to the selected stresses of the material group, to which the material belongs, using the aforementioned simple rules. A merit of the calculation method is that it allows the most efficient design for a specific application using the allowable stresses for the actual material selected for the application. The two methods are based on different assumptions, and as a consequence the detail of the analysis is different. Both methods offer a safe and proven method of designing pressure-bearing components for valve shells. This document has been prepared by Technical Committee CEN/TC 69 "Industrial valves". The responsible German standardizing body is Working Committee NA 003-01-01 AA "Grundnormen" ("Basic standards") at DIN Standards Committee Valves (NAA).