Why standards are replaced – and what stays valid

Four interests that slow every replacement

A standard is never just a document. Behind it stand tooling, drawings and inspection plans at the manufacturer, spare-parts lists and plant documentation at the operator, specification libraries and calculation templates at the designer – and at the stockholder a warehouse sorted by the old number. Every change costs all four something, and none of them ordered the new standard.

That is why unifying standards is so hard even where it would be technically simple. Change a dimension and stock becomes unsaleable; change a designation and drawings become ambiguous; change a test level and old certificates become incomparable. Standards work knows these interests and has developed mechanisms that make the transition bearable.

The mechanisms: coexistence, withdrawal, dimensional continuity, grandfathering

Coexistence period. A European standard is published, the conflicting national standard remains valid alongside it for a while; the date of withdrawal is the deadline by which the CEN members must withdraw the national standard. During this period catalogues and contracts carry both numbers.

National forewords and A-deviations. The German edition of an EN carries a national foreword saying which DIN standard is replaced and what has changed; A-deviations record where national law requires something different. For purchasing, the foreword is often more useful than the standard itself.

Grandfathering. A plant stays under the standard it was built to. The withdrawal of DIN 2633 does not invalidate a single flange in an existing line – it only changes what the spare part is ordered to today. The replacement tables say which number that is: DIN 2633 becomes EN 1092-1 type 11, PN 16.

Dimensional continuity. The most important mechanism for the warehouse: the new standard carries over the dimensions of the old. EN 1092-1 took over the PN series and bolt circles of the DIN flanges, EN 10220 the outside diameters of DIN 2448 – the weld neck flange type 11 is dimensionally identical to the old DIN 2633 flange, only the name changes. Where dimensional continuity is missing, the replacement becomes a construction site; the standards comparison shows per component from which edition the comparison holds.

Two lessons: ISO 7005-1 and EN 1759-1

ISO 7005-1 – the failure. Since 1992 the ISO flange standard tried to unite PN series and Class series in one document, a world standard for flanges. Neither world adopted it: the PN plants in Europe and the Class plants in America would still have needed their own spare parts, and a document containing both spares nobody the changeover. The 2011 edition still exists – orders are placed to EN 1092-1 or ASME B16.5.

EN 1759-1 – the success. Europe did not displace the Class flanges but brought them into its own workshop: EN 1759-1 describes flanges with Class designation and the dimensions of ASME B16.5, with European materials and European certification. Whoever operates a Class-system plant in Europe gets a spare part from an EN – without rebuilding the plant. That is the kind of unification that works: it leaves the existing valid.

The lineage of our range shows the same experience on a small scale: DIN 2448 merged with its outside diameters into EN 10220, the flange standards DIN 2627 to DIN 2638 into EN 1092-1 with bolt circles carried over, DIN 2605-1 into EN 10253-2 with a long coexistence period, and the Whitworth pipe thread of DIN 2999 lives on in EN 10226-1. Wherever the dimensions stayed, the changeover was a matter of designation – not of stock.

Further reading

The standards-worlds topic: How binding standards are · Standards worlds by region · EN and ASME compared · Mixing standards worlds · Standards translator · Materials between the worlds.

From our knowledge base: Standards guide · ASME and ASTM profiles · EN 1092-1 versus ASME B16.5 · ASME flange dimensions · Standards comparison · Inspection documents to EN 10204 · Reading markings · Identifying a component.