This Standard is applicable to uncoated cylindrical steel sheaths with a corrugated profile and with a nominal internal diameter of up to 130 mm 1) and their connectors (couplers) which are assemblied to form ducts for presstressing tendons in post-tensioned prestressed concrete elements. It is only applicable to sheaths and connectors made of interlocked or welded steel strip 2)3). The seals required between sheaths and couplers are not covered by this standard4). 1) For diameters greater than 130 mm requirements should be drawn up on the basis of this standard and agreed upon by the parties involved. 2) In case of coated or galvanised steel additional provisions have to be considered, which are not covered by this standard. 3) For plastic sheaths, see Annex A. 4) The appropriate rules will be specified in a seperate European Standard for concrete structures which is under preparation.