Fernando Lidonnici Convenor of WG’C’/CEN TC54 Sant’Ambrogio Servizi Industriali SRL - Milano The advantages of the new calculation methods provided in the harmonized Pressure Vessel Standard EN Part 3. Comparison with the national standards used up to now.

Determination of the Nominal Design Stress for Steels in Service Conditions

From the point of view of the nominal design stresses : EN permits higher stresses for: Carbon and Low Alloy Steels Austenitic Stainless Steels

Nominal Design Stress for CS Plates with Rm=410 MPa

Nominal Design Stress for CS Plates with Rm=510 MPa

Nominal Design Stress for SS Plates type 304

Fine Grained Steels For Fine Grained Steels the present issue of EN still provides a safety factor of 2,4 on the room temperature tensile strength: the problem will be solved shortly with an amendment already approved.

Nominal Design Stress for Fine Grained Steels with Rp0,2 = 460 MPa

2,5 Cr- 1 Mo Steels For Cr-Mo steels of large thickness subject to heat treatment the values of the ASME code are higher than the values in the corresponding EN standards: these values however are not guaranteed and therefore they are not reliable.

Nominal Design Stress for 2,5Cr-1Mo Steels

Domed Ends There is an advantage in using EN for domed ends, particularly at higher pressures. At low pressure the formulae of the ASME Code may be less conservative.

Minimum Thickness of Korbbogen End with PS=5 bar

Minimum Thickness of Korbbogen End with PS=10 bar

Minimum Thickness of Korbbogen End with PS=50 bar

Minimum Thickness of Korbbogen End with PS=100 bar

Cylinders under External Pressure Either under vacuum or at higher external pressures EN permits lower thicknesses than ASME for a given unsupported shell length.

Minimum Thickness of Stainless Steel Shell under Vacuum at 150°C

Minimum Thickness of Stainless Steel Shell under 10 bar Ext. Pressure at 150°C

Conical Reducers of constant thickness EN permits lower thicknesses particularly at higher pressures. It also permits greater angles without transition knuckle.

Conical Reducers PS=5 bar

Conical Reducers PS=10 bar

Conical Reducers PS=50 bar

Flanges: The alternative method of Annex G is a definite progress in respect of the old Taylor Forge and DIN methods. Although further gasket parameters are needed, the savings in thickness and weight may be substantial.

9 Examples of Welding Neck Flanges designed with different methods – Input Data for the Design

Minimum required Bolting Size / Flange Weight according to different Methods for the 9 Examples

Heat Exchanger Tubesheets: The alternative method of Annex J is a definite progress in respect of the old Gardner’s theory. The savings in thickness and weight may be substantial, particularly for fixed tubesheet heat exchangers.

8 Examples of H.E. Tubesheets designed with different methods – Input Data for the Design

8 Examples of H.E. Tubesheets designed with different methods Resulting Tubesheet Thicknesses

DESIGN BY ANALYSIS: The “Direct Route” of Annex B permits to ignore secondary stresses in all cases where there is no need to consider them (constant loading conditions).This is a substantial advantage in the design of structures where the classic DBA (based on elastic analysis) caused an unnecessary increase in thickness.

SECONDARY STRESSES AT THE CONNECTION BETWEEN A CYLINDRICAL SHELL AND A CIRCULAR FLAT END (Note: In DBA based on elastic analysis and stress categorization the Flat end thickness must be increased in order to limit secondary stresses on the shell)

CONCLUSIONS -EN is the most advanced Pressure Vessel standard in the world. -It permits substantial economies in Pressure Vessel Construction. -Using a single European Pressure Vessel standard means a greater competitiveness for the European industry: the most important Users and Notified Bodies must be convinced that it is now time to replace the old Pressure Vessel standards with EN All the resources of the interested industry must be put on the further development of EN 13445: the further development of the old national Pressure Vessel codes is a waste of resources that goes against the interests of Europe.