Methods of manufacturing flanges and rings

PN‑EN 1092‑1:2018

The PN‑EN 1092‑1:2018 “Flanges and their joints. Circular flanges for pipes, valves, fittings, accessories and equipment, PN‑designated. Part 1: Steel flanges” defines the basic engineering requirements for steel flanges used in industrial piping systems and steel equipment.

Methods of manufacturing flanges and rings depending on the base material according to PN‑EN 1092‑1:2018

In Clause 5, Table 1 of the PN‑EN 1092‑1 standard specifies the base materials permitted for the manufacture of a given type of flange or ring. The first base material described in the table as “Forged”, and further specified as seamless rolled, pressed, and forged, is the only material, in terms of manufacturing methods, from which any flange and ring compliant with the requirements of PN‑EN 1092‑1 may be manufactured. By contrast, the second base material listed in the table, “Cast”, may be used to manufacture only two types of flanges compliant with PN‑EN 1092‑1, namely Type 21 – integral flange and Type 34 – welding neck loose ring.

Table 1 is of fundamental importance for determining the conformity of flanges and rings with the PN‑EN 1092‑1 standard, as it links a given flange with the base material and its corresponding material standard, for example for forged materials this is the appropriate part of PN‑EN 10222, and for plates PN‑EN 10028. The manufactured flange must meet the requirements for mechanical properties specified in the relevant material standard, and all limitations defined in those standards must be observed.

The determination of the base material is also of key importance when flanges and rings are intended for use in pressure equipment. In such cases, they must be manufactured from materials that meet the safety requirements of the applicable European Pressure Directives. A list of all material standards that comply with pressure equipment regulations (Directive 2014/68/EU) can be found at the following website: Implementing Decision – EU – 2025/165 – EN – EUR‑Lex. The PN‑EN 1092‑1 standard also includes, in Table 9, a list of steel grades divided into material groups and base material types suitable for the manufacture of flanges compliant with European Standards and meeting the requirements of the Pressure Equipment Directive (PED). In addition, Annex D of the standard contains a list of materials commonly used in industry that are not compliant with European Standards and, consequently, with the requirements of the Pressure Equipment Directive; however, these materials may be used in pressure equipment provided that the formal requirement of individual approval is met, either in the form of a European Approval of Materials (EAM) or a Particular Material Appraisal (PMA).

The provisions of Clause 5, which are significant for determining the base material that may be used for the proper manufacture of a specific type of flange or ring in accordance with PN‑EN 1092‑1.

• Rings of Types 35 to 37 should be manufactured exclusively from austenitic or austenitic‑ferritic steels (material groups 10–16 according to Table 9).

• Mechanical properties depend on the dimensions of the unfinished components, defined as “vR” for forgings and “t” for flat products. As a result of machining, these dimensions are reduced. For machined flanges and rings, the thickness dimensions C1 to C4 or F should not be less than 80% of dimension “vR” for forgings and 80% of dimension “t” for flat products. Any deviations from the above requirements should be subject to agreement between the manufacturer and the purchaser.

• Except for weld repairs carried out in accordance with Clause 5.11, repair by welding is permitted only on the basis of the purchaser’s written consent. The material or component certificate should include records confirming that approved welding procedures and welder qualifications were applied.

MANUFACTURING METHODS

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_a Seamless rolled, pressed, forged.

_b Only one radial weld is allowed under DN 1800. If using cut strips for manufacturing, the through thickness direction of the strip for type 11 and 34 shall be perspendicular to the flange centerline, for Type 01, 02, 04 and 32 in the direction of the flange centreline.

_c For welding: see 5.11.

_d In case flanges are made by cold forming of a base material e.g. flat product, some mechanical properties, like elongation after fracture (A) and impact energy (KV), will be impaired due to cold forming without subsequently heat treatment.