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A.2.4 Qualification test requirements

A.2.4.1 General

A procedure test bend shall be produced on the nominated bending machine and shall be subject to the relevant PBHT.

The following data shall be determined and shall be reported.

A.2.4.2 Ripples on intrados of the bend

The intrados of the bend shall be examined visually; if any ripples are detected they shall conform to the requirements of 7.3.10.

A.2.4.3 Surface defects

The outer surface of the bend shall be examined and shall be shown to conform to the requirements of 7.3.11.

Visual examination shall be applicable to all material groups. In addition, steel groups 2 and 6 shall be exam­ined for transverse imperfections on the outside diameter of the bend by means of magnetic particle inspection to EN ISO 17638:2009. For steel conforming to steel group 8, dye penetrant inspection to EN 571­1:1997 shall be used in place of magnetic particle inspection.

The results are to be valued after acceptance level 2X according to (PT) of EN ISO 23277:2009 or (MT) of EN ISO 23278:2009.

A.2.4.4 Bend geometry

The tube bend geometry shall conform to the requirements given in 7.3.4, 7.3.5 and 7.3.7.

A.2.4.5 Hardness test

For hot formed bends, or bends requiring post-bending heat treatment, the hardness at the extrados of the bend shall be measured after completion of the heating process. The hardness measured shall be not more than 80 HV 10 higher than the hardness of the un-deformed material.

A.2.4.6 Mechanical tests

For hot formed bends, or bends requiring post-bending heat treatment, the hardness at the extrados of the bend shall be measured after completion of the heating process. The hardness measured shall be not more than 80 HV 10 higher than the hardness of the un-deformed material.

A.2.4.7 Gang bending of tube panels

The tube bends produced by the gang bending method shall comply, in all respects, with the requirements of tubes bent singularly.

The gang bending method shall be qualified by a tube bending procedure test which is valid for the specific gang bending machine being utilised. The tube panel used in the test shall consist of at least three tubes which have been welded together prior to gang bending.

A.3 Cold formed bends in tubes with outside diameter >142 mm

A.3.1 Types of bending processes

The bending process is normally characterised by specific machines using different forms of tooling. A change to a similar machine, of different load capacity, using the same tooling shall not require re-qualification.

A.3.2 Post bending heat treatment

Bends shall be subject to PBHT in accordance with 7.3.8 and 7.3.9 prior to testing.

Separate qualification shall be required for:

1. cold bend (without PBHT);

2. cold bend (with PBHT).

A.3.3 The validity range of the test

The test carried out shall also cover a range of tube bending parameters above and below those tested.

The range for diameter and thickness shall be as follows:

• tested outside diameter d_o covers diameters within the range 0,5 x d₀ to 1,8 x d_o,

• tested thickness e covers thicknesses within the range 0,7 x e to 1,5 x e.

The tube bending ratio rjd_o used during the test shall cover all higher bending ratios as follows:

Test ratio rJd₀ of 1,8 covers rjd_o of 2,0; r_bld_o of 2,5 etc.

where r_b is the radius of the bend which has been tested.

A.3.4 Qualification test requirements

A.3.4.1 General

A procedure test bend shall be produced on the nominated bending machine and shall be subject to any relevant PBHT.

The following data shall be determined and shall be reported.

A.3.4.2 Ripples on intrados of the bend

The intrados of the bend shall be examined visually. If any ripples are detected, they shall conform to the requirements of 7.3.10.

A.3.4.3 Surface imperfections

The outer surface of the bend shall be examined and shall be shown to conform to the requirements of 7.3.11.

Visual examination shall be applicable to all material groups. In addition, steel groups 2 and 6 shall be examined for transverse imperfections on the outside diameter of the bend by means of magnetic particle inspection according to EN ISO 17638:2009. For steel conforming to steel group 8, dye penetrant inspection according to EN 571-1:1997 shall be used in place of magnetic particle inspection.

The results are to be valued after acceptance level 2X according to (PT) of EN ISO 23277:2009 or (MT) of EN ISO 23278:2009.

A.3.4.4 Bend geometry

The tube bend geometry shall conform to the requirements of 7.3.6 and 7.3.7.

Measurements for DFC shall be taken at 30° intervals around the bend. Wall thickness measurement may be performed by using an ultrasonic technique.

A.3.4.5 Hardness test

For cold formed bends which require post-bending heat treatment, the hardness at the extrados of the bend shall be measured after completion of the heating process. The hardness measured shall not be more than 80 HV 10 higher than the hardness of the un-deformed material.

A.3.4.6 Mechanical testing

Cold formed bends which require post-bend heat treatment other than stress relieving, shall be sectioned to provide mechanical tests, as follows:

• tensile test at room temperature in accordance with EN ISO 6892-1:2009;

• Charpy V-notch tests (if so required by the base material standard) in accordance with EN ISO 148-1:2010.

The number and position of the specimens shall be as specified for the base material. The resulting values shall be in accordance with the relevant base material standard or data sheet.

A.4 Hot formed bends in tubes with outside diameter >142 mm

A.4.1 Types of bending processes

The bending process is normally characterised by specific machines using different forms of tooling. A change to a similar machine, of different load capacity, using the same tooling shall not require requalification.

A.4.2 Post bending heat treatment

Bends shall be subject to PBHT in accordance with 7.3.8 and 7.3.9 prior to testing.

Separate qualification shall be required for:

1. heating by an induction processes;

2. heating by gas or other forms of furnace/muffle.

A.4.3 The validity range of the test

The test carried out shall also cover a range of tube parameters above and below those tested.

The range for diameter and thickness shall be as follows:

• tested outside diameter d₀ covers diameters within the range 0,5 x d₀ to 1,8 x d₀,

• tested thickness e covers thicknesses within the range 0,7 x e to 1,5 x e.

The tube bending ratio rjd_o used during the test shall cover all higher bending ratios as follows:

• test ratio rdd₀ of 1,8 covers r_bld_o of 2,0; rjd_o of 2,5 etc.

where r_b is the radius of the bend tested.

A.4.4 Qualification test requirements

A.4.4.1 General

A procedure test bend shall be produced by the nominated process and shall be subject to the specified PBHT.

The following data shall be determined and shall be reported.

A.4.4.2 Ripples on intrados of the bend

The intrados of the bend shall be examined visually. If any ripples are detected they shall conform to the requirements of 7.3.10.

A.4.4.3 Surface imperfections

The outer surface of the bend shall be examined and shall be shown to conform to the requirements of 7.3.11.

Visual examination shall be applicable to all material groups. In addition, steel groups 2 and 6 shall be examined for transverse imperfections on the outside diameter of the bend by means of magnetic particle inspection according to EN ISO 17638:2009. For steel conforming to steel group 8, dye penetrant inspection according to EN 571-1:1997 shall be used in place of magnetic particle inspection.

The results are to be valued after acceptance level 2X according to (PT) of EN ISO 23277:2009 or (MT) of EN ISO 23278:2009.

A.4.4.4 Bend geometry

The tube bend geometry shall conform to the requirements of 7.3.6 and 7.3.7.

Measurements for deviation from circularity shall be taken at 30° intervals around the bend. Wall thickness measurement may be performed by using an ultrasonic technique.

A.4.4.5 Mechanical testing

A.4.4.5.1 General

The test bend shall be sectioned to provide the following test specimens. The results of the tests shall be recorded.

A.4.4.5.2 Metallographic examination

Longitudinal microsections shall be taken from the un-deformed section of the tube and from the bend centre for evaluation by optical microscopy up to x 1 000. A single sample shall be prepared from the straight material (see Figure A.1 (a)) and samples taken from the intrados (see Figure A.2 c)) and extrados (see Figure A.2 b)) of the bend.

No cavities or structural abnormalities shall be permitted.

A.4.4.5.3 Definitive and comparative tests

A.4.4.5.3.1 General

Charpy V-notch impact tests shall be performed in accordance with EN ISO 148-1:2010 if required by the base material standard.

A.4.4.5.3.2 Definitive tests

Test conditions:

1. straight tube, transverse Charpy V-notch specimens; notch vertical to the surface, test temperature: RT or 0 °С (as for base material specification) close to the surface, Figure A. 1, position 6, one set of three specimens;

2. bend centre, transverse Charpy V-notch specimens; notch vertical to the surface, test temperature: RT or 0 °С (as for base material specification) close to the surface, Figure A.2 position 4 and position 5, one set of three in each position.

The minimum value shall be in accordance with the requirements of the base material specification or data sheet.

A.4.4.5.3.3 Comparative tests

If the results of the test obtained under A.4.4.5.3.2 are inconsistent, comparative tests, below, shall be carried out.

These tests shall be carried out at 100 °С in order to reduce the scatter of the impact energy values. The values are for comparing the test results taken from the bend with those of the straight portion of the tube and are not for determining absolute values for the material.

Test conditions:

1. straight tube, longitudinal Charpy V-notch specimens; notch in parallel with the surface, close to the surface, test temperature: 100 °С, Figure A. 1, position 1, one set of three specimens;

2. bend centre, longitudinal Charpy V-notch specimens; notch in parallel with the surface, close to the surface, test temperature: 100 °С, Figure A.2, positions 2 and 3, one set of three specimens from each position.

The difference between the mean values of positions 2 and 3 shall not be greater than 30 % of the value at position 1.

A.4.4.5.4 Tensile test in accordance with EN ISO 6892-1:2009

Transverse tensile test specimens shall be taken in straight tube, Figure A.1, position 7 and in the centre of the bend, position 8 and position 9, as shown in Figure A.2 (test temperature RT).

The results of the test shall conform to the material specification or data sheet.

Key

1 see A.4.4.5.3.3 a)

6 see A.4.4.5.3.2 a)

7 see A.4.4.5.4

a) see A.4.4.5.2

Figure A.1 — Specimens from straight portion of the tube

Key

2, 3 see A.4.4.5.3.3 b)

4, 5 see A.4.4.5.3.2 b)

8, 9 see A.4.4.5.4

2. see A.4.4.5.2

3. see A.4.4.5.2

Figure A.2 — Specimens from bent portion of tube

Annex В
(informative)

Welded pressure connections and non-pressure containing attachments

The welded connections and joint preparations included in EN 1708-1 (for pressure-containing parts), EN 1708-2 (for non-pressure containing parts), EN ISO 9692-1 (for welded joints by means of arc processes) and EN ISO 9692-2 (for welded joints by submerged arc welding) provide a range of appropriate information regarding joints for water-tube boilers.

For examples of connections for the welding of unstayed flat ends see EN 12952-3:2011, 10.3.

The manufacturer is responsible for the interpretation of the details for application to his own designs based on his past experience and good engineering practice. In selecting the appropriate detail to use for each type of connection, consideration should be given to the service conditions under which it will be required to function. It will be necessary in each case for the manufacturer to ascertain the connections selected are of adequate strength and are suitable for the welding process used.Annex C
(normative)

Manufacture of welded tubewalls

C.1 General

These requirements apply to the manufacture of various types of gas-tight welded tubewalls commonly used in boiler construction.

C.2 Methods of manufacture

C.2.1 General

The manufacturing processes commonly used are given below. These cover the fabrication of tubewall panels by use of welding, and involve the joining of fins to tubes, or fins to fins.

C.2.2 Tubes finned by welding

Two basic methods shall be adopted as follows:

• the welding of tubes together by the insertion of a fin (bar steel) between them. The closure welds are between the edges of the fin and the adjacent tubes, see Figures C.1 a), C.1 b) and C.1 c);

• individual fins (bar steel), of half the fin space width welded to each tube to form a series of finned tubes. The closure welds are between the edges of the abutting fins, see Figure C.1 d).

C.2.3 Integrally finned tubes

The closure welds shall be between the edges of the abutting fins, see Figure C.1 e).

Such tubing shall be supplied directly by the tube manufacturer. It is available with the fins having been pro­duced by a rolling or an extrusion process. The finned tube shall be subjected to an acceptance test generally in accordance with EN 10216-2. Additionally, further testing shall be required to ensure that fin twisting, centreline deviation and off-set are contained within the limits set by the manufacturer, to ensure that dimensional requirements and weld quality can be achieved.

C.2.4 Other methods

Other types of construction may be employed provided they shall be shown to meet the requirements of C.5 and C.6.

C.3 Allowable materials

C.3.1 Tubes

Tubes used for tubewall construction shall be supplied in accordance with the requirements of EN 12952-2.

C.3.2 Fins

Fins shall be made from plate, flat rolled wire or bar steel. Suitable non-alloy steels shall be in accordance with EN 10025-2 e.g. S235JR and S275JR. Low-alloy steels shall be in accordance with EN 10028-2. Other steels may be used in accordance with the manufacturer's own proven procedures which shall ensure that, by their use, the safety of the boiler is not impaired.

C.3.3 Filler materials

The filler metal used shall be compatible with the tube and fin materials and shall satisfy the requirements of EN 12952-2. For tubewalls to be used at elevated temperatures, the filler metal shall be of the same type as the tubing, or shall conform to the nearest lower alloy consistent with the type of material to be welded.

C.4 Manufacturing processes and controls

C.4.1 Welding process

The selection of the welding processes used shall be at the discretion of the manufacturer and shall depend on the material, tube dimensions, manufacturing process and the welding conditions involved.

Acceptable welding processes include, for example:

• manual metal arc using covered electrodes;

• gas shielded metal arc;

• submerged arc;

• tungsten inert gas.

C.4.2 Specific requirements for manufacturers

C.4.2.1 Surface cleanliness

In order to obtain a satisfactory connection between the tube and the fin it is necessary for the surface of the tube and fin, within the welding zone, to be cleaned to a level suitable for the welding process to be used.

C.4.2.2 Fin to tube attachment welds

1. Un-penetrated tube wall thickness <?_r

The weld penetration shall be such as to leave either

1. a minimum of 2 mm of un-penetrated tube wall thickness e_r which may be achieved by the pre­selection of an appropriate tube wall thickness or

2. an un-penetrated wall thickness of less than 2 mm, but not less than the minimum calculated thickness given in EN 12952-3.2011, 11.3. In this case, post-weld heat treatment shall be applied in accordance with the requirements of Tables 10.4-1 and 10.4-2.

2. Weld attachment of the fin to tube

Partial penetration welds shall be permitted. The tube to fin welded joints, of the types shown in Figures C.1 a) to C.1 d) inclusive, shall be such as to ensure adequate heat transfer from the fin into the tube wall. For the welding processes listed in C.4.1, this condition shall be considered to be satisfied, if the values indicated in Figure C.2 at the partial penetration weld are achieved.

C.4.2.3 Welding imperfections in fin to tube welds

The limits for welding imperfections shall be in accordance with Table C.1.

C.4.2.4 Site welding

Any site welding between the tube wall panels directly to the tube surface shall be limited to the small areas of make-up fin local to the tube butt welds between panel ends. This restriction is not valid for the welding-on of non-pressure containing weld attachments to the membrane walls like, e.g., sheet metal boxes or bearing­type fixtures.

C.4.3 Heat treatment

C.4.3.1 Pre-heating

Where pre-heating is required, it shall be carried out in accordance with 10.3.

C.4.3.2 Post-weld heat treatment

Where post-weld heat treatment is required, it shall be carried out in accordance with Tables 10.4-2 and 10.4-3.

C.5 Welding procedure approvals

A welding procedure approval test shall be performed, by the production of a test panel consisting of not less than three tubes, to demonstrate that the welding is in accordance with the requirements of EN ISO 15613 and the geometry and weld quality are in accordance with the requirements of this annex.

C.6 Production tests

Prior to the commencement of a production run²), a production test shall be performed to demonstrate compliance with the requirements given in Figures С.2, C.3 and C.4.

Any significant changes in welding parameters or equipment occurring during a production run shall be sufficient cause to require an additional production test.

C.7 Non-destructive examination (NDE)

NDE shall be limited to 100 % visual examination of all fin to tube welding.

Table C.1 — Limits for weld imperfections in fin to tube welds