http://www.documentbays.org/89980-bs-en-12952-3-2011.html

11.5.4 Limit of intensity in the case of radial loadingThe intensity of radial loading shall not exceed that given by Figure 11.5-2 for tensile or Figure 11.5-3 for compressiveattachment loadingwhereq is the greatest intensity of radial load, in Newtons per millimetre;f is the design stress of the tube material as used in 11.1, in megapascal;et – c1 is the minimum tube thickness i.e. nominal thickness less allowance, in millimetres;do is the outside diameter of the tube in millimetres;α is the angle subtended by the attachment at the tube centre in degrees (see Figure 11.5-1).11.6 Fitting and joining of heated tubes11.6.1 Fitting of tubesFitting of tubes to drums or headers shall be in accordance with EN 12952-5:2011, 8.11 or 9.4.11.6.2 Joining of heated tubesJoining of heated tubes shall be done by butt welds in accordance with EN 12952-5:2011, 8.11. Socket welds,sleeve welds, flanges and screwed joints shall not be used.11.7 Joining of unheated tubes11.7.1 GeneralUnheated tubes shall be joined by welded or integral flanges, butt welds, socket welds, or screwed and sealwelded joints. Screwed flanges and sleeve welds shall not be used. Flanges shall not be used where the boltswould be exposed to products of combustion. See also EN 12952-5:2011, 8.11 and 9.4.