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The manufacturer shall maintain records showing the position, length, width and depth of all repairs carried out on:

1. drum longitudinal and circumferential butt welds and nozzle welds;

2. header longitudinal and circumferential butt welds;

3. butt welds in integral tubes over 25 mm thickness or over 170 mm outside diameter.

Repairs made to other welds shall be recorded in the relevant NDE report.

Pre-heating shall be in accordance with 10.3.

Post-weld heat treatment shall be in accordance with 10.4.

Welded components which are subjected to normal methods of manufacture and comply with the requirements of 10.4.1.4, 10.4.1.5 and 10.5 would not be expected to suffer unacceptable degradation of material property values during heat treatment. Attention is, however, drawn to the fact that welds in components which are subjected to normalizing heat treatment may suffer property degradation.

When testing material after heat treatment for components designed to operate in the proof strength range at elevated temperatures, base material values up to 5 % lower than the specified minimum yield strength and the specified minimum tensile strength shall be permitted in individual cases. Values lower than the specified minimum yield strength and the specified minimum tensile strength by between 5% and 10 % shall be permitted if it can be demonstrated that:

1. the heat treatment has been performed correctly;

2. the requirements regarding base material elongation after fracture have been met;

3. the requirements regarding base material impact energy have been met;

4. the component wall thickness is adequate for the design with the proof strength value obtained.

For components designed to operate in the creep range values lower than the specified minimum yield strength and the minimum specified tensile strength shall be permitted up to a maximum of 10 %.

Special cases may arise when it is necessary to weld to a pressure part after the final post-weld heat treatment has been completed, e.g. the welding of isolated minor attachments and effecting isolated minor repairs¹). This practice shall be permitted on steel groups 1.1, 1.2, 5.1 and 5.2 in accordance with CEN ISO/TR 15608 provided that the welding complies with an approved welding procedure specification in accordance with the requirements of EN ISO 15614-1, taking into account the following requirements:

1. minimum pre-heating shall be in accordance with 10.3. For steels 5.1 and 5.2 the preheating temperature shall be > 200 °С;

2. either hydrogen controlled welding electrodes, shall be used or, alternatively, TIG welding shall be used;

3. where practicable, at least two runs of welding should be performed. For Cr-Mo steel at least two runs shall be applied;

4. the throat thickness of attachment welds shall not exceed 13 mm;

5. for Cr-Mo steels the nozzle dimensions shall not exceed 57 mm outside diameter by 10 mm thick;

6. the weld metal shall blend smoothly with the component material and shall be dressed if required;

7. after completion of all welding and, if necessary, dressing as required, the welds shall be examined by magnetic particle test.

8. the special requirements for the seal welding of expanded tubes are given in 9.4.

permanently marked (see 6.4.2).

Where a butt welded joint is required between plates of different thicknesses, the thicker plate shall be reduced in thickness by one of the methods shown in Figures 8.9-1 and 8.9-2. The thicker plate shall be trimmed to a smooth taper as indicated in Figures 8.9-1 and 8.9-2 including, where necessary, the width of the weld. If necessary the required taper shall be obtained by adding additional weld metal beyond the width of what would otherwise be the edge of the weld. Where UT testing is required, adequate measures shall be taken to ensure the weld can be suitable scanned.

a) Shell to shell joint

I

2. Shell to end joint-end thicker than the shell

2. Shell to end-joint thinner than the shell

Key

a < 15° see also EN 12952-3:2011, Figure 10.2-4.

a is Ri or r

I is the parallel length

1. is the position of weld

NOTE 1 In cases a) and b), the position of the weld (1) and the parallel length I is in accordance with the manufacturer's normal practice.

NOTE 2 Tapers may include the weld if desired, but no taper is required if the difference in thickness is less than 3 mm

NOTE 3 Internal and external tapers need not be symmetrically disposed.

NOTE 4 For typical details of welded connections see Annex B.

Figure 8.9-1 — Butt welds in plates of unequal thickness with middle lines coincident

1. Shell to shell joint

2. Shell to end joint

NOTE 1 In cases a) and b), the position of the weld (1) and the parallel length I is in accordance with the manufacturer's normal practice.

NOTE 2 Tapers may include the weld if desired, but no taper is required if the difference in thickness is less than 3 mm.

NOTE 3 Internal and external tapers need not be symmetrically disposed.

NOTE 4 Tapers may be inside or outside the vessel.

NOTE 5 For typical details of welded connections see Annex B.

Figure 8.9-2 — Butt welds in plates of unequal thickness with middle lines offset

8.9.1.7 Production control test plates for boiler drums shall be in accordance with of EN 12952-6:2011,

Clause 8.

The extent of non-destructive examination of flat end plate welds as specified in EN 12952-3:2011, 10.3 shall be in accordance with EN 12952-6:2011, Clause 9.

Not less than two runs of metal shall be deposited at each weld. Each run of weld metal shall be clean and free from slag before the next run is deposited.

Permanent backing rings shall not be used.

Fusible inserts shall not be regarded as backing rings. Fusible inserts shall be used only if the material from which they are made is compatible with the parent metal and if they are completely fused into the joint.

Where the use of partial penetration welds is specified, the depth of penetration shall be given on the drawing.

The surface of the completed weld shall be free from irregularities between weld runs and the final finish of all welds shall be such that the change of section between the parts is gradual and free from sharp notches and significant undercutting, see EN 12952-6:2011, 9.3.5.

Attachment welds of branches, nozzles and stubs on drums and headers shall not involve any combination of austenitic and ferritic steels although minor instruments connections made from austenitic steels are permissible. Composite tubes shall have the composite layer removed at the weld end preparation before they are welded towards any drum or header. It is not allowed to melt any austenitic steel into the weld pool, when the carbon steel component is welded.

NOTE Guidance concerning typical welded connections is given in Annex B.

All pads, reinforcing plates, manhole frames, and other attachments which contribute to the strength of the pressure part, shall fit closely and the gap at all exposed edges to be welded shall not exceed 2 mm or 5 % of the thickness of the attachment at the point of attachment, whichever is the greater.

Where reinforcing plates or manhole frames are fitted, they shall be provided with tell-tale holes through the outer plate.

Manhole frames of the pressed type shall bed closely to the surfaces to which they are to be connected and shall be fillet-welded to the inner surface of the drums.

Manhole frames which are set through the drum plates shall be either formed in one piece without welding, or formed from a suitable rolled section fabricated by fusion welding provided they are stress relieved after welding and before attachment to the drum, unless the whole drum is to be stress relieved on completion. The welds shall also be subjected to non-destructive examination in accordance with EN 12952-6:2011, Clause 9. Butt welded manhole frames positioned on the shell shall be such so that the welds are in a plane at right angles to the longitudinal axis to the drum.

Except where specific dimensions are shown on the drawing, the maximum gap between the outside of any branch or shell and the inside edge of the hole in the shell, flange, reinforcing ring or backing ring shall not exceed 1,5 mm for openings up to 300 mm, and 3 mm for openings over 300 mm.

NOTE To achieve this gap, the outside diameter of the shell or nozzle may be machined over a sufficient length to accommodate the attachment to which it is to be welded.

The attachment of non-pressure parts (e.g. brackets, lugs stiffeners, supports, flats, including drum internal fittings) to drums and headers by welding shall be permitted.

The welds of attachments designated as load carrying, see EN 12952-3:2011, 5.9, shall be continuous. These welds shall be around the perimeter of the attachment, and may be double sided partial penetration welds, a single-sided full penetration weld or double-sided full penetration welds. The type of joint selected shall be subjected to the relevant NDE as specified in EN 12952-6:2011, Clause 6.

It is permissible for the welds of non-load carrying attachments to be made by intermittent fillet welds.

When multi-run welding is employed, each run of weld metal shall be cleaned to ensure a sound weld before the next run is deposited.

Preheating and post-weld heat treatment shall be applied in accordance with 10.3 and 10.4 respectively.

In addition to conforming to the appropriate parts of 8.1 to 8.8, the following requirements shall be applied to the welding of tubes.

Irrespective of the type of steel, root runs shall be made without interruption other than for the changing of electrodes or filler metal, or to allow the welder to re-position himself. Welds requiring preheat, which are made at site, shall not be allowed to cool until the thickness of the weld metal deposited exceeds one third of the final thickness.

When welding other than carbon or carbon manganese steels, if an unavoidable interruption becomes necessary, preheating temperatures shall be maintained during the interruption. If this is not possible, the joint shall be wrapped in a dry insulating blanket to ensure slow cooling. Preheat shall be re-applied before further welding is commenced.

NOTE 1 It is strongly recommended that any interruptions to the welding should be avoided whenever possible.

NOTE 2 Completed root runs made in the workshop, may be allowed to cool provided that precautions are taken to

ensure slow cooling e.g. by wrapping in a dry insulating blanket.

In order to minimize the risk of hydrogen cracking, on completion of the welding, especially with higher alloy Cr-Mo steels and in thick materials, the joint shall be wrapped in dry thermal insulating blankets to ensure slow cooling, unless any specified post-weld heat treatment is to be applied immediately, or if preheating is to be maintained.

If the proximity between two butt welds for tubes with diameters up to and including 250 mm is less than twice the outside diameter and for tubes with an outside diameter over 250 mm less than 500 mm, both butt welds then have to be heat treated together after welding.

The welding of tube joints conforming to this European Standard shall include matching, if necessary, by the manufacturer of the tube ends at each joint.

Matching of the bores shall be effected by selection, drifting (hot or cold), machining, swaging or by use of a suitable expander. Any machine counter boring required shall not reduce the thickness of the tube wall to below the design thickness. All hot drifted ends shall be heat treated in accordance with requirements of the relevant material standard, or data sheet, as appropriate.

The bores of the ends of adjacent tubes should preferably match exactly. Permissible limits for bore difference and bore misalignment are given in Table 8.11-1.

Table 8.11-1 —Alignment tolerances of tube bores

Any centre line angular misalignment should not normally exceed 3°, i.e. 5 mm in 100 mm, (see Figure 8.11-1), but shall in any case be consistent with any specific design requirements.

Key

^a centre line of weld

Figure 8.11-1 — Angular alignment of butt welded tubes

Segmental and cut-and-shut type bends shall not be permitted.

Permanent backing rings shall not be used in the tubes of the evaporative circuit.

Temporary steel or non-metallic backing rings, which are compatible with, or inert to, the parent tube material, may be used. These shall be removed completely after the completion of welding.

When back purging is specified in the welding procedure specification, the air shall be removed from the vicinity of the weld by the admission of a sufficient volume of purging gas such that oxidation of the root zone is prevented. Purging shall be carried out by passing the purging gas though the full length of the tube, or by local purging, using temporary dams. Such dams shall removed by the manufacturer after the completion of welding.

Not less than two runs of metal shall be deposited at each weld. Each run of weld metal shall be clean and free from slag before the next run is deposited.

Permanent backing rings shall not be used.

Fusible inserts shall be permitted and shall be used only if the material from which they are made is compatible with the parent metal and if they are completely fused into the joint.

The surface of the completed weld shall be free from non acceptable imperfections and the final finish of all welds shall be such that the change of section between the parts is gradual and free from sharp notches and undercutting in excess of that permitted by EN 12952-6:2011, 9.3.5.

Preheating, where required, shall be carried out in accordance with 10.3.

Welds attaching branches, nozzles and stubs to tubes shall not involve any combination of austenitic and ferritic steels.

NOTE Guidance concerning typical methods of attachment of nozzles branches and connections are given in Annex B.

The welds of attachments designated as load carrying (see EN 12952-3:2011, 5.9) shall be continuous. This weld shall be a fillet weld around the perimeter of the attachment, a partial penetration weld, a single-sided full penetration weld or a double-sided full penetration weld. The type of joint selected shall be subjected to NDE as specified in EN 12952-6:2011, Clause 9.

It is permissible for the welds of non-load-carrying attachments to be made by intermittent fillet welds.

When multi-un welding is employed, each run of weld metal shall be cleaned to ensure a sound weld before the next run is deposited. Preheating and post-weld heat treatment shall be applied when required by 10.3 and 10.4 respectively.

The flash butt welding of tubes shall be in accordance with the requirements of the appropriate European Standard.

In the absence of such a European Standard the use of nationally or internationally recognized standards for the flash butt welding of tubes shall be permitted.

The methods of construction of water wall panels and the required controls are given in Annex C.

Welding procedure qualifications, welder qualifications and pre-production tests for arc stud welding shall be generally in accordance with the requirements of EN ISO 14555. In each case qualifications shall include macro tests. Studs made of high alloy material may have hardness values in the weld which exceed the limitations given in EN ISO 15614-1:2004, Table 2.

Process control shall be monitored, as a minimum, by the "Simplified Production Test" described in EN ISO 14555:2006.

For stud welds on tubes with outside diameters less than 80 mm, an incomplete weld rag shall be acceptable, provided there is no gap between the tube surface and the stud.

9 Mechanical connections

Mechanical connections are those which do not involve strength welding between the connected parts (see also EN 12952-3:2011, 8.4 or 8.5).

All drums, headers and other large parts of boilers shall be provided with manholes, headholes, handholes, or other inspection openings as appropriate, to permit internal examination and effective cleaning. It is permissible to provide openings to facilitate manufacture and maintenance.

NOTE Access may be gained for these purposes by cutting and re-welding tubes or blind nozzles. Inspection openings may, where necessary, be closed by nozzles with welded caps.

For calculation pressures exceeding 1,8 MPa, openings in pressure parts with mechanical closures shall be of the internal door type. For calculation pressures of 1,8 MPa and below, circular external or elliptical doors of the blanked flange type is permitted.

The minimum sizes of access openings, together with the associated restrictions on nozzle or ring height, are given in EN 12952-7:2002, 4.6.4.

Internal doors shall be made from steel in accordance with EN 12952-2 and constructed in accordance with the following:

1. doors shall be formed to fit closely to the internal joint surface and shall be fitted with studs, nuts and crossbars;

2. doors for circular openings larger than 250 mm diameter or elliptical or rectangular openings larger than 250 mm x 175 mm shall be provided with two studs. Doors for openings of these sizes and below may be provided with one stud. Doors for openings not larger than 123 mm diameter or 123 mm x 90 mm may have the stud forged integrally with the door;

3. door studs shall be made from steel of a quality that may be welded and have a minimum tensile strength of not less than 355 MPa. Studs used for manhole doors shall not be less than 30 mm diameter. The studs shall be fixed to the door by one of the following methods:

1. screwed through the door and fillet welded on the inside;

2. let through the door and fillet welded each side of the door with a weld of leg length not less than 10 mm;

3. attached to the door by an intermediate plate or lugs with the strength of the attachment not being less than that of the stud and designed to prevent the studs from turning;

4. provided with an integral collar, screwed into blind holes in the door and shall be prevented from turning;

4. when the door is in a central position the spigots should have an all-round clearance of approximately 1,5 mm, but at no point shall the clearance exceed 3 mm. The spigot depth shall be sufficient to trap the gasket;

NOTE 1 For the selection of gasket materials see EN 12952-7:2002, 4.6.6.

5. nuts shall comply with the appropriate European Standard and be faced on the seating surface;

6. crossbars shall be made from steel in accordance with EN 12952-2 having a minimum specified tensile strength of not less than 355 MPa. The seating surface shall be faced: