Pipe dreams

After 59 years, the British Standard for screwed and socketed steel pipes, BS 1387, is due to be withdrawn in June next year. It will be replaced by a new European standard. For designers the change will make little difference – the new standard maintains the same technical performance requirements as the old BS. Specifiers, however, need to be aware of the changes called for under the new standard if they are to avoid making costly mistakes.

In the move to common European standards, the single British Standard has in effect become two.

BS 1387 was not just about the supply of screwed or plain end tubes, it also contained requirements for sockets, tubulars (a pipe fitting made of tube), and fittings. The tube content is now the scope of EN 10255 and the fittings content of EN 10241. Common to both of these standards is the pipe thread requirements, which is the scope of EN 10226. This standard consists of three parts that jointly supersede BS 21 specification of pipe threads for tubes and fittings.

So what’s changed?

Finish While the emphasis on presentation is different, the same combinations of end finish and coatings are available in both standards. BS 1387 is written around the supply of screwed and socketed or plain end tubes in the varnished condition, with options for other end finishes or coatings. The new standard, EN 10255, is written around the supply of plain end tubes in a bare and uncoated condition with options to specify other end finishes and coatings. The capability to use the product with threaded, grooved or compression type fittings is also maintained.

Strength grade The strength grades are virtually identical. EN 10255 is written for the supply of a single strength grade defined as S195T. The grade has yield strength of 195 N/mm^2, tensile of 320-520 N/mm² and an elongation of 20%. These are directly equivalent to the requirements in BS 1387 of yield 195 N/mm^2, tensile of 320-460 N/mm² and elongation 20%.

Testing Although there are very small changes to some of the detail, the new standard maintains the same technical performance requirements as BS 1387. On the key issue of leak testing, both BS 1387 and EN 10255 require a hydraulic test at pressure of 50 bar or an electro-magnetic (eddy current) test. The test requirements are equal and which test method is selected is up to the manufacturer. Finished tubes to EN 10255 are, for all practical purposes, unchanged when supplied to the requirements of BS 1387.

Size range and description EN 10255 introduces two new types of tubes, Type L and Type L1, which are light tubes. The European standard’s Type L2, medium and heavy tubes correspond to BS 1387’s light, medium and heavy gauge tubes. This revised range also represents the combination of types used in ISO 65 (L1,L2, M and H) and requirements from the French tube standards.

The principal difference between the two standards is not in the tube size but in their description. The European standard describes pipes using outside diameter and thickness or thread size (R), and series (L, L1, L2, M, H) . The table over the page shows the comparison and relative descriptors for the range and thicknesses. In addition, a new 10.2 mm diameter (6DN) tube has been added to EN 10255.

Weld bead EN 10255 requires the external weld bead to be trimmed flush, whereas BS 1387 has no requirements for weld bead trim. In the European standard, the internal weld bead is limited to not more than 60% of the specified wall thickness, except when supplied as suitable for galvanising or galvanised when the bead height is limited to 0.3 mm+ 0.05T (where T refers to the nominal thickness of the tube).

Tube markings EN 10255 requires the tube to be marked with: the manufacturer’s mark; W or S (welded or seamless); and series/type (H, M, L2, L1 or L). The series/type marking can be replaced by colour banding: H – red, M – blue, L2 – brown, L1 – white and L – green, the same as used by BS 1387.

Certification Unless otherwise stated, EN 10255 requires tubes to be supplied with an inspection document type 2.1 (a simple certificate of compliance with no test data) in accordance with EN 10204. Alternatively tubes can be supplied with an inspection document type 2.2 in accordance with EN 10204, which includes a typical tensile test result representative of the material and the ladle (cast) analysis of the material. Conformity to the requirements of order is to be checked by non-specific inspection and testing in accordance with EN 10021. CE marking, which shows the products conform to the mandate, will be mandatory after June 2006. BS 1387 does not require a certificate unless requested, when an inspection document type 2.1 is to be supplied.

Transition to the new standards

Because of the Construction Products Directive, the usual method of issuing a EN standard, approved by standardisation body CEN, no longer applies. Normally, when a new CEN approved standard is issued the conflicting national standard must be withdrawn within six months. The EN standard is then adopted in the member state as a national document, so in Britain EN 10255 would become BS EN 10255.

However, because this standard is affected by the Construction Products Directive the process is more laborious. For a product to be accepted for use in construction it must be shown to satisfy the requirements of the directive, relating to issues such as strength, weldabilty, resistance to fire and durability.

Once compliance has been established, there then follows a three-month period for national standards bodies to formally adopt the harmonised EN standard into regulations (ie to become a BS EN). This is followed by three months for it to be published. There then follows a three-month period for the harmonised standards to be announced in the EU’s Official Journal. From this point a transition period of 12 months is set when the harmonised standard will coexist with current national standards. During this time CE marking may be applied to the products. At the end of the 12 months, the national standard is withdrawn and only the harmonised standard may be used.

EN 10255 was approved by CEN on 27 May 2004 and made available as BS EN 10255 on 24 August 2004. The standards are now in their coexistence period and BS 1387 will be withdrawn in June 2006.

CE marking

The table above shows the information required for compliance with CE marking, which must be included in the commercial documents by the manufacturer. The CE marking of products, while mandatory in most of Europe, will not be mandatory in the UK as the Building Regulations recognise there is more than one way of proving that a product meets the requirements. However, where products are used throughout Europe and the UK and the product has a harmonised European standard, CE marking will be the norm.

Design and specification implications

The new standard maintains the same technical performance requirements as BS 1387 so there are no design implications. However changes will be required in specifications and other contract documents where BS 1387 should be replaced by EN 10255. Tubes should be specified by outside diameter and thickness or thread size (R) and series (L, L1, L2, M, H).

Eddie Hole is the manager of technical marketing at Corus Tubes’ Structural & Conveyance Business