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Any material damaged metallurgically in the process of cutting to size or forming the edge or end preparation shall be removed by machining, grinding, chipping or thermal-cutting back to sound metal.

Surfaces that have been thermally cut shall be cut back by machining or grinding so as to remove all burnt metal, harmful notches, slag and scale, but slight discoloration of machine thermally cut edges on mild steel shall not be regarded as detrimental. If alloy steels are prepared by thermal cutting, the surface shall be dressed back by grinding or machining for a distance of at least 1,5 mm, unless it can be shown that the material has not been damaged by the cutting process.

NOTE These requirements for dressing do not apply to surfaces that are prepared for electro-slag welding, where a thermally cut surface is generally acceptable without further treatment.

After the edges of the material have been prepared for welding, they shall be visually examined for flaws, cracks, laminations, slag inclusions or other defects before further work is carried out. Any weld repairs that are required to materials damaged as a result of thermal cutting shall be to an approved welding procedure specification.

Drums, headers and ends shall be rolled or pressed from plate, solid forged, drawn or extruded, or made by a combination of these processes. Components made by a forging, drawing or extrusion process shall be produced in accordance with the forgemaster's specification, as agreed with the boiler manufacturer.

Components formed from ferritic steel plate shall be heat treated in accordance with 10.2.2 to 10.2.4 inclusive. The heating associated with forming operations and the heat treatment requirements after forming are given in 10.2.

The forming requirements applicable to austenitic steel plate are the subject of development. In the meantime, the methods used shall be in accordance with the manufacturer's own proven procedure which shall ensure that, by their use, the safety of the boiler is not impaired.

Shell plates shall be formed, either hot or cold, to ensure compliance with the tolerances specified in 7.4. Each shell plate shall be formed to the correct contour up to the extreme edges of the plate. The bending or pressing shall be done entirely by machine. The definitions of hot and cold forming are given in 3.1 and 3.2.

Local heating and hammering shall not be employed.

Dishing and peripheral flanging, either hot or cold, shall be carried out to ensure compliance with the tolerances specified in 7.4. The operations shall be performed by machine. Sectional flanging shall not be employed.

Where practicable, shells and ends shall be rolled or pressed from one piece of plate. Where this is impracticable, butt welding of plate, prior to forming shall be permitted, provided that the welded joints are non-destructively examined after forming in accordance with the requirements of EN 12952-6:2011, and a welding procedure qualification test has been performed to EN ISO 15614-1:2004 taking into account any heat treatment cycles involved. A production test plate as specified in 10.2.5 shall be provided.

Extruded openings in headers shall have a fillet with a radius not less than the thickness of the neck of the extrusion.

Tubes which are bent hot or cold shall conform to 7.3.2 to 7.3.12.

This subclause does not apply to fittings in accordance with EN 10253-2:2007 and EN 10253-4:2008.

NOTE Annex A requires procedure tests to be carried out on tube bends. Attention is drawn to the fact that not all the combinations of materials and bending processes permitted, and the associated thermal treatments nominated in Table 7.3-2, will satisfy the requirements for the procedure test given in 7.3.2 to 7.3.13 and Annex A. The manufacturer should ensure that any combination of material, bending process and the chosen bend geometry will produce bends that satisfy the requirements of 7.3. If a chosen bend geometry is found not to comply with the requirements of 7.3, the manufacturer should adjust the design to enable the requirements to be met.

It shall be demonstrated by means of a tube bending procedure test (see Annex A) that tubes can be satisfactorily bent to the requirements of 7.3.1. The tests shall be performed to represent combinations of tube sizes, materials and bend radii which demonstrate the adequacy of the bending method chosen. The range and scope of the qualification of tube bends resulting from these procedure tests are also given in Annex A. The results from the bending procedure tests shall be documented and used as a basis for all future tube bends falling within the scope of the combinations tested.

When specific pre-production test bends are manufactured in accordance with Table 7.3-1 and which conform to the requirements of 7.3.1 the resulting documented data shall serve as qualification for subsequent production runs and may be considered to satisfy the requirements of Annex A.

NOTE Documented evidence of previous satisfactory tube bending procedure tests may be accepted as fulfilling these requirements.

Thinning at the bend extrados, thickening at the bend intrados (where required) and departure from circularity limits shall be demonstrated by the methods given in Table 7.3-1.

NOTE This test relates to the forming of tubes for conventional water-tube boilers. For the special case of coiled boilers and coiled superheaters, see Annex D.

Table 7.3-1 — Requirements for dimensional testing of a production run of tube bends

The thickness at any point after bending shall not be less than that given by equation:

2

(7.1)

r_bI do + 0,5

=

ext

<?_acl X—

^act2r_b!do +

where

e_ext is the required minimum thickness at the extrados, in mm;

e_act is the nominal thickness of the supplied tube minus the supplier's maximum negative thickness tolerance, in mm;

r_b is the radius of the bend measured to the centre-line of the tube in mm;

d₀ is the nominal outside diameter of the tube, in mm.

When the measured value on the tube bend is less than e_ext reference shall be made to the minimum calculated thickness given in EN 12952-3:2011, 11.3.

The thinning on the extrados of bends formed in two stages i.e. hot formed after initial hot or cold bending, shall not exceed 30 % of the thickness of the straight tube local to the bend as measured during a procedure test.

The thickness at any point after bending shall not be less than that given by equation: where

^{— e}

act

2r_bI do- 0,5

^X 2r_b/Jo-l

(7.2)

e_jnt is the required minimum thickness at the intrados, in mm;

e_act is the nominal thickness of the supplied tube minus the supplier's maximum negative thickness tolerance, in mm;

r_b is the radius of the bend measured to the centre-line of the tube, in mm;

d₀ is the nominal outside diameter of the tube, in mm.

When the measured value on the tube bend is less than e_int reference shall be made to the minimum calculated thickness given in EN 12952-3:2011, 11.3.

For tubes above 142 mm diameter comparison shall be made directly with the calculated thickness given in EN 12952-3:2011, 11.3. The calculated thickness shall be stated on the drawing.

The departure from circularity of tube bends shall be calculated from the equation:

do — do _

и

(7.3)

= 2x— —ХІ00

do + do

where w is the departure from circularity, in %;

do is the maximum outside diameter measured at the tube bend apex, in mm;

do is the minimum outside diameter measured at the same cross-section as do, in mm.

The permitted departure from circularity shall be within the limits given in Figures 7.3-1 and 7.3-2.

1. the departure from circularity of tube bends, which are bent in a single continuous operation, shall not exceed the limits shown in Figure 7.3-1;

2. the departure from circularity of tube bends on tubes not exceeding 80 mm nominal outside diameter, which are bent by a double operation i.e. hot pressed after the primary bending operation then post-bend heat treated in accordance with Table 7.3-2, shall not exceed the limits shown in Figure 7.3-2.

Key

^a departure from circularity и

^b ratio rjd_o

Figure 7.3-1 — Limits of departure from circularity for single operation bending

Key

^a departure from circularity и

^b ratio rtJd₀

Figure 7.3-2 — Limits of departure from circularity for double operation bending

The post-bend heat treatment (PBHT) of hot or cold formed bends shall be in accordance with the following rules:

1. all hot formed tube bends and cold formed bends requiring heat treatment after bending, including bends hot formed after cold bending, shall be heat treated in accordance with the requirements of 7.3.9 except as defined in b) or e) below;

2. hot formed tube bends in steel group 1, with outside diameters of 80 mm or less, need not receive a post­bend heat treatment if it can be demonstrated that the bending operation was completed within the normalizing range as defined in the relevant base material standard, or data sheet, as appropriate;

3. all cold bent tube bends with thinning greater than 25 % as measured in the procedure test, shall be heat treated in accordance with the requirements of 7.3.9;

4. PBHT of cold formed tube bends in accordance with Table 7.3-2 shall be carried out in accordance with the requirements of 7.3.9;

Table 7.3-2 — Post-bend heat treatment applicable to cold formed tube bends

5. post-bend heat treatment may be waived if it can be demonstrated by a suitable procedure test, that heat treatment shall not be required;

6. for hot formed bends local post bend heat treatment of the tube bend shall not be acceptable. Any post­bend heat treatment involving normalising shall encompass the bend and adjacent straight lengths of the tube.

With the exception of those cases in accordance with 7.3.8, all tube bends shall receive a post-bending heat treatment as follows:

1. Hot formed bends

All hot formed bends, including bends which have been hot pressed after cold forming, shall be heat treated in order to restore the material properties to their optimum condition. The post bending heat treatment applied shall be in accordance with the requirements given in the relevant base material standard, or data sheet, as appropriate.

For hot formed bends local post bend heat treatment of the tube bend is not acceptable. Any post bend heat treatment involving normalising operation shall encompass the bend and adjacent straight lengths of tube.

2. Cold formed bends

When a stress relief heat treatment is specified in the case of normalized and tempered or quenched and tempered materials, the requirements for tempering given in the relevant base material standard, or data sheet, shall be followed as appropriate.

When a stress relief heat treatment is specified in the case of normalized only materials, the requirements for post-weld heat treatment given in Tables 10.4-2 and 10.4-3 shall be followed.

Other stress relief heat treatment methods may be used if it can be demonstrated to be adequate by means of the procedure test.

Post-bending heat treatment will normally not be required for cold bent austenitic tubing.

Hot formed tube bends of austenitic tubes inclusively bends which are formed by two operations require a new heat treatment by solution annealing and subsequently and adequately accelerated cooling using water and air according to the material specification.

NOTE The heat treatment process should take account of measures to ensure no component deformation.

Ripples are multiple waves like undulations on the intrados of tube bends, see Figure 7.3-3.

Deviations from the nominal bend profile are local isolated deviations from a smooth normal profile of the intrados of the bend, e.g. irregularities sometimes found at the commencement of mandrel assisted bends in small diameter tubes.

1. In tubes up to and including 80 mm nominal outside diameter, ripples shall not be acceptable. Deviations from nominal bend profile may be accepted provided the departure from circularity at the peak and trough of the deviation meets the requirements of 7.3.7;

2. for tubes above 80 mm nominal outside diameter up to and including 142 mm nominal outside diameter, ripples and deviations from the nominal bend profile shall not be permitted;

3. tubes with nominal outside diameters greater than 142 mm shall be permitted to contain ripples on the intrados of the bend within the limits shown in Figure 7.3-3, provided they have a smooth profile and blend into the surface of the bend. Deviations from the nominal bend profile shall not be permitted.

d₀, d_o2, d₀3, do4, etc is the actual outside diameter of the tube at the position being measured.

NOTE For clarity, the ripples have been exaggerated.

Figure 7.3-3 — Ripples on tube bends

For such ripples to be acceptable, both the following conditions shall be satisfied:

Amplitude of the ripples h_m- 0,5 (c/₀2 ⁺ <4й) - <7₀з ^< 0,03 d₀ (7.4)

Wave pitch a > 12 h_m (7.5)

The surface of tube bends shall be free of defects such as cracks, indentions, laps and scabs. Surface defects may be removed by grinding. In such cases the resulting thickness shall not be less than the minimum calculated thickness given in EN 12952-3:2011, 11.3.

The surface of the tube bend shall be such as to permit effective visual examination.

Areas of the tube bend which have been ground to remove defects shall be examined by surface flaw detection methods to ensure that complete removal of the defect has been effected.

Repairs to the tube surface by welding are generally not permitted. However, in special cases of tubes of 142 mm nominal outside diameter and above, such repairs may be acceptable, when supported by an approved welding procedure specification and taking into account the following:

1. the extent of the zone to be repaired;

2. the grade of the material involved;

3. the diameter and thickness of the bend;

4. the heat treatment conditions involved;

5. the operating temperature of the tube bend.

The tube bends produced by the gang bending method shall conform, in all respects, with the requirements of tubes bent singly, see A.2.4.7.

The departure from circularity shall be measured during production on the two outermost tubes of the panel.

The results shall be compared with the requirements of 7.3.7. For practical reasons, do in the Equation (7.3) should be replaced by the outside diameter of the tube measured straight.

The bending procedures adopted for metallurgically bonded composite materials tubing shall be in accordance with the requirements of 7.3. In addition, any special requirements recommended by the tube manufacturer shall be taken into consideration.

1. Cold formed reducers

Ferritic tubing with d₀< 100 mm may be cold formed by reducers. The procedure should be proved by a test.

When forming leads to an increase of material hardness of > 80 HV10, the formed parts should be annealed at a temperature being in accordance with those indicated in Table 10.4-2.

2. Hot formed reducers

Reducers of ferritic tubing with d₀ > 100 mm are to be manufactured by hot forming. This procedure should be proved by a test. Hot reduced tubes should be treated like hot formed bending (see 7.3.9.1 a)). Reduced tubes being normalized or heat-treated, should undergo heat treatment completely.

1. Cold formed reducers

Cold formed reducers of austenitic tubing are to be treated like cold formed tube bending in accordance with 7.3.9.2.

2. Hot formed reducers

Hot formed reducers of austenitic tubing should completely undergo a new heat treatment with the appendent undeformed tube according to the material specification.

7.4 Drum and header fabrication tolerances

Middle line and surface alignment tolerances shall be permitted as follows, where e_a is the actual thickness of the thinnest plate at the joint.