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The root faces of the weld preparations shall be aligned within the tolerances permitted by the welding procedure specification and the components shall be aligned as indicated on the drawings within the following tolerances.

1. For longitudinal joints in cylindrical components, the middle lines of adjacent plates shall be aligned within the tolerances given in Table 7.4-1.

Table 7.4-1 — Offset of middle lines for longitudinal joints in cylindrical components

2. For circumferential joints, the middle lines of adjacent plates shall be aligned within the tolerances given in Table 7.4-2.

Table 7.4-2 — Offset of middle lines for circumferential joints in cylindrical components

1. not exceed the maximum tolerances:

1. For longitudinal joints given in Table 7.4-3

Table 7.4-3 — Offset of surfaces of longitudinal joints in cylindrical components

2. For circumferential joints given in Table 7.4-4

Table 7.4-4 — Offset of surfaces of circumferential joints in cylindrical components

or

2. if the maximum alignment tolerances in a) are exceeded, they may be reduced by tapering the surface(s) at a slope no steeper than that permitted by 8.1.1.1b) or 10.2.2.4 of EN 12952-3:2011, as appropriate, over a width that includes the width of the weld.

Either of the following methods of tapering shall be permitted:

1. building up the surface of the thinner plate with added weld metal in accordance with an approved welding procedure specification to provide the required taper; or

2. tapering one or both of the thicker plate surfaces.

The tapering method of 2) shall not be permitted if it would reduce the plate thickness below the specified minimum or the component at the location in question.

The diameter of a drum shall not deviate from the nominal diameter by more than ± 1 %.

The difference between the maximum and minimum internal diameters at any one cross section shall not exceed 1 % of the nominal internal diameter. If the drum is made of plates of unequal thicknesses, the measurements shall be corrected for plate thicknesses, as they may apply, to determine the diameters at the middle line of the plates.

Irregularities in profile, checked using a template embracing an arc of 20°, shall not exceed 3 mm plus 5 % of the minimum plate thickness. A 25 % increase in the maximum value shall be permitted if the length of the irregularity does not exceed one quarter of the length of the shell ring with a maximum of 1 000 mm.

There shall be no flats at welded seams and any local departure from circularity shall be gradual. Small departures from circularity may be rectified by cold rolling. However, any non-destructive examination as required by EN 12952-6 shall be carried out after the cold rolling operation.

The maximum deviation of the complete shell from a straight line shall not exceed 0,3 % of the total cylindrical length. Measurements shall be made to the surface of the parent plate and not to a weld, fitting or other raised part.

The requirements of 7.4.2.1 shall apply.

The requirements of 7.4.2.2 shall apply.

Variations in thickness (thinning) arising during manufacture shall be gradual. In no case shall the thickness of the end be less than the design thickness given in EN 12952-3:2011, 10.2.

The depth of dishing, measured from the plane passing through the point where the straight flange joins the knuckle radius, shall in no case be less than the theoretical depth, nor shall this depth be exceeded by more than 1,25 % of the diameter, for diameters of ends up to and including 3 000 mm. Variations of the profile shall not be abrupt, but shall merge gradually into the specified shape. The knuckle radius shall not be less than specified, and shall have common tangents with both the straight flange and the dished profile, at each junction.

8 Welding

The following special requirements specific to welding shall be considered before any manufacturing is commenced.

NOTE 1 General guidance on welding of ferritic steels is given in EN 1011-1 and EN 1011-2 as well as for austenitic steels in EN 1011-3 which may be used to supplement the welding requirements of this European Standard.

NOTE 2 CEN ISO/TR 15608 describes the principle of group classification regarding weldable materials which have comparably typical characteristics. CEN ISO/TR 20172 includes the detailed assignment of the EN-materials to groups being based on this European Standard.

The selection of materials for the pressure parts, and for any attachments to be made to them, shall be such that any welding operations which are to be carried out will not render the component unfit for its intended duty.

The selection of welding consumables shall be such as to ensure the cross-weld strength required by the design is achieved. The affects of post-weld heat treatment on the completed joint as given in 8.7, shall also be taken into consideration.

The dimensioned drawings of main pressure parts shall include the location of all main joints and attachments to be made to the components, clearly showing details of the main joint weld preparations, all attachment welds, and their location relative to the longitudinal and circumferential joints and openings.

Welding of the joints of the component parts of a water-tube boiler shall only be undertaken when the following conditions are satisfied:

1. welding procedure specifications shall be compiled by the manufacturer in accordance with EN ISO 15609 for each joint or family of joints;

2. the welding procedure specifications selected by the manufacturer shall be approved for the field of application;

3. the welders and welding operators shall be qualified for the work allocated to them and their approvals shall be valid.

Where the use of oxy-acetylene welding is proposed, the manufacturer shall demonstrate that the location of such welds in the boiler will not result in subsequent problems in the operation. The method of procedure approval shall be in accordance with the requirements of EN ISO 15614-1 or EN ISO 15613. Welder approval shall be in accordance with the requirements of EN 287-1.

Butt welds shall not be permitted on the bends of tubes, except in the special case of coil boilers - see Annex D.

The toes of welds of attachments to main pressure parts should, wherever practicable, not be located closer than 40 mm to main joint welds.

If, for reasons of design, this spacing cannot be achieved the welds shall be capable of being non- destructively examined within the area of influence of the attachments and the welds shall be ground to a smooth profile to remove all notches in this area.

Where local grinding of the welds is required, as indicated above, the ground surface shall be 100 % non- destructively examined in accordance with the requirements of EN 12952-6:2011, Clause 9.

If this latter condition is not practicable, the attachment weld shall cross the main joint weld completely. In such cases, the surface of the main joint weld and the attachment welds shall be ground locally after the welding-on of the attachment has been completed.

The portion of attachment welds which crosses main joint welds shall be treated as "load-carrying" with respect to the non-destructive examination to be applied. Such NDE shall be carried out in accordance with the requirements of EN 12952-6:2011, 9.1.4.

Openings for branches should, if practicable, be positioned away from main joint welds of drums and headers. The spacing shall be considered adequate if the distance between the edge of the main joint weld and the edge of the branch or set on reinforcement fulfils the requirements given in Table 8.1-1.

Table 8.1-1 — Spacing between branches and main joint welds

If, for reasons of design, these spacings cannot be achieved the welds shall be capable of being non- destructively examined within the area of influence of the opening and the welds shall be ground to a smooth profile to remove all notches in this area.

Where local grinding of the welds is required, as indicated above, the ground surface shall be 100 % non- destructively examined in accordance with the requirements of EN 12952-6:2011, Clause 9.

The machining of holes in longitudinal butt welds shall not be permitted. Holes machined through the centre of circumferential butt welds shall be permitted, provided that the welds have been subjected to non-destructive examination in accordance with the requirements of EN 12952-6:2011, Clause 9, over the length of the seam to be machined.

When boiler drum strakes cannot be manufactured from single plates they shall be completed with the minimum number of longitudinal joint welds. Non-destructive testing of main joints, see EN 12952-6:2011, Clause 9, shall be performed after any forming/re-rolling and if applicable heat treatment operations have been completed.

Where any parts of the boiler drum are to be made in two or more strakes, the welding of the longitudinal joints shall be completed before the welding of the connecting circumferential joints is commenced. The longitudinal joints of adjacent strakes shall be staggered unless the construction of the drum makes this impracticable e.g. thick and thin profile.

The welding on site of widely differing materials, e.g. austenitic to ferritic materials, should be avoided whenever possible.

Where necessary, staging and protection from the weather shall be provided to enable the welding operations to be performed under satisfactory conditions.

During production, a copy of the welding procedure specification shall be placed at welders/operators working place.

Electrodes, filler wires, filler rods, fluxes, fusible inserts, shielding and purge gases shall either:

1. comply with the relevant European Standards; or

2. where relevant European Standards do not exist, comply with the relevant national standards.

The manufacturer shall ensure that the correct consumables, as stated in the welding procedure specification, shall be used during manufacturing operations.

All consumables including gases shall be stored and handled with care, and used in accordance with the conditions specified by the consumable manufacturer.

NOTE This is particularly important in the case of the requirements for baking and drying when hydrogen controlled consumables are to be used.

Electrodes, filler wires, filler rods and fusible inserts that show signs of damage or deterioration, such as cracked or flaked coatings or rusting or dirty electrode wire, shall not be used. Fluxes shall be clean and dry.

Approval of fusion welding procedure specifications shall be carried out in accordance with EN ISO 15614-1 or EN ISO 15613 (see EN 12952-6:2011, Clause 6).

For all procedure qualification welds electrical welding data shall be recorded.

Limits related to the scope of heat-input according to WPS defined in EN ISO 15614-1.

EN ISO 15614-1:2004, 8.4.8, shall be required for materials used at boiler pressure parts according to material group 4 and group 2 according to CEN ISO/TR 15608 with joint thickness more than 30 mm.

For definition of heat input limits related to the WPS for multi-layer welds the minimum respectively maximum values of all single layers shall be evaluated.

The welding procedures for the butt welding of metallurgically bonded composite materials tubing shall be in accordance with the requirements of EN ISO 15613. In addition, any special requirements recommended by the tube manufacturer shall be taken into consideration. The procedures shall be qualified using composite materials tubing complying with the same specification as the tubing to be used on the boiler.

Welders and welding operators approval shall be carried out in accordance with EN 287-1:2011 and EN 1418:1997, 4.2.1 and 4.2.2 respectively (see EN 12952-6:2011, Clause 7). The training, supervision and control of welders and welding operators shall be the responsibility of the manufacturer.

Welders involved in the buttwelding of metallurgically bonded composite materials tubing shall be approved in accordance with the requirements of EN 287-1.2011 and EN 1418:1997, 4.2.1, 4.2.2 respectively. In addition, any special requirements recommended by the tube manufacturer shall be taken into consideration. The approval shall have been carried out using composite materials tubing complying with the same specification as the tubing to be used on the boiler.

The fusion faces and the adjacent material on the inner and outer surfaces shall be dry and thoroughly cleaned of grease, oil, lubricants, marking paints, oxide scale or other foreign substances to a clean metal surface for a distance from the welding edges sufficient to prevent contamination of the weld. Appropriate compatible materials shall be used for cleaning purposes.

To maintain, during welding, the specified alignment (see 7.4.1) and, where required, the details for any root gap given in the drawings and welding procedure specifications (see 8.1.3), the parts to be welded shall be securely held in position by mechanical means, welded bridge pieces or tack welding.

NOTE The dimensions of the root gap are the dimensions after any tack welding.

It is recognized that there may be difficulty in complying strictly with the requirements for the root gap. Minor modifications imposed by practical considerations shall be permitted, provided the manufacturer can ensure that the safety of the boiler is not impaired.

Correction of irregularities in fit-up shall not be carried out by hammering.

Temporary attachments welded to the pressure parts shall be kept to a practical minimum.

Temporary attachments (except hydraulic testing blanks) shall be removed prior to the first pressurization unless they have been designed to the same requirements as permanent attachments. The removal technique shall be such so as to avoid, as far as practicable, impairing the integrity of the pressure part and shall be by chipping, grinding or thermal cutting followed by chipping or grinding. Any rectification necessary by welding of damaged regions after removal of attachments shall be undertaken by approved welders working to an approved welding procedure specification.

All temporary attachments shall be removed. The associated weld area shall be ground flush and examined by a surface flaw detection method appropriate to the material before any stress relief heat treatment is applied.

The preheating requirements of 10.3 shall be applied and maintained during tack welding and the welding of bridge pieces or other attachments.

Filler materials used for tack welding shall be of a designation appropriate to the particular weld and shall be deposited in accordance with an approved welding procedure specification.

Particular attention shall be paid to the quality of tack welds which shall be deposited by approved welders. Where necessary, the ends of these tack welds shall be dressed by grinding or chipping to facilitate proper fusion if they are to be incorporated into the root run. Any cracked tack welds shall be completely removed.

While arc strikes are to be avoided, any accidental arc strikes shall be ground smooth and the parent material examined by a surface flaw detection method appropriate to the materials.

A list of welders and welding operators, together with records of their approval tests, shall be retained by the manufacturer who may be required to provide evidence of approval of any welder engaged in the fabrication of water-tube boilers.

If it is found necessary to repair a weld, an approved welding procedure and an approved welder shall be used. The nature and extent of such repairs shall be reported as part of the manufacturer's data dossier. For the examination of films or other records of NDE all previous relevant records of the repaired areas shall also be available. Details of weld repairs shall be made available to non-destructive examination personnel responsible for re-examination.

Defects shall be cut out by an appropriate method. Where welds are partially removed, the portion cut out shall be sufficiently deep and long to remove the whole defect. At the ends of the cavity, there shall be a gradual taper from the base of the cut to the surface of the weld metal. The width and profile of the cut shall be such as to give adequate access for re-welding.

If the whole of the weld is removed and the butt weld re-welded, a new production test plate shall be provided if required by EN 12952-6:2011, 8.2.

When butt welds have been repaired, the component and the test plates (if any) shall be heat treated in accordance with the relevant clauses of this European Standard, and the test plates (if any) shall be tested in accordance with EN 12952-6:2011, Clause 8.

All repaired areas and re-welded joints shall be subjected to non-destructive examination in accordance with EN 12952-6:2011, Clause 9, and shall be subjected to the same testing and inspection requirements as the original joints.