NOTE 2 Eyebolts with suitable lugs on the door plate, or headed bolts engaging with slotted sections on the door plate, may be used instead of studs.
External doors
Circular external doors of the blank flange type shall be designed in accordance with the requirements of EN 12952-3:2011, 10.4. The design shall incorporate a spigot and recess of sufficient dimensions to completely trap the gasket.
NOTE For the selection of gasket materials see EN 12952-7:2002, 4.6.6.
Branches and nozzles mechanically connected to the main pressure parts
Scope and restrictions
The following methods of mechanically connecting branches or nozzles to the main pressure part shall be permitted:
expanding and belling; restricted to branch and nozzle outside diameters not exceeding 48,3 mm (for tube connections see 9.4);
expanding and seal welding; restricted to steels having a carbon content not exceeding 0,25 % (product analysis) and branch and nozzle outside diameters not exceeding 48,3 mm (for tube connections see 9.4);
screwing or screwing and seal welding directly into the pressure part; subject to the requirements of EN 12952-3:2011, 8.5.1;
screwing or screwing and seal welding into a socket; subject to the requirements of EN 12952-3:2011, 8.5.2 and 8.5.3, or;
by studs; subject to the requirements of EN 12952-3:2011, 8.4.
Screwed connections
The requirements of EN 12952-3:2011,8.5 shall apply.
Studded connections
Studs shall be designed in accordance with the requirements of EN 12952-3:2011, 8.4.5. The design shall ensure that high fatigue strength is achieved and shall have a full thread engagement in the main pressure part equal to at least one diameter of the stud. Studs shall not completely pierce the pressure part and, after allowing suitable clearance at the blind end of the stud, the unpierced material of the pressure part shall amount to not less than one quarter of the stud nominal diameter.
After the machining of the jointing faces, the final thickness of the pressure part shall not be less than the minimum thickness required by EN 12952-3:2011, Clauses 7, 8, 9 or 10, as appropriate.
Tube connections
Expanded connections
It shall be permissible to attach tubes to drums and headers other than by welding. Attachment shall be made by expanding, expanding and belling, or provided the requirements of b) are satisfied, by expanding and seal welding. The method of expanding is normally by use of mandrels.
It is also permissible to use other methods of expanding but in such cases it shall be demonstrated that the method provides adequate leak tightness and will prevent tube withdrawal in service. The provision of documented evidence of satisfactory performance in service shall be considered as satisfying these requirements.
The nominal outside diameter of the tube connected by expanding shall not exceed 114,3 mm.
Attachment by expanding may be achieved with or without the use of expansion grooves (see Figure 9.4-1).
When expanded joints are to be seal welded the following restrictions shall be observed:
the drum or header material shall be limited to steel groups 1.1, 1.2 or 5.1 (see CEN ISO/TR 15608);
the welding pre-heat temperature shall be in accordance with 10.3;
the fillet weld shall be made with a minimum of two runs with the stops/starts staggered between runs;
the fillet weld size shall not exceed 8 mm;
either hydrogen controlled welding electrodes shall be used or, alternatively TIG welding shall be used;
the welding procedure shall be supported by a welding procedure qualification in accordance with EN ISO 15614-1;
when the room temperature yield strength of the drum or header material is in excess of 300 MPa further expansion of the joint shall be applied after seal welding to reduce the local shrinkage stresses in the joint;
surface crack detection of the seal weld shall be carried out in accordance with the requirements of EN 12952-6:2011, Clause 9;
tube holes for expanded tubes shall provide a region of parallel seating of not less than 13 mm and shall be formed in such a way that the tubes can be effectively tightened in them. The surface finish shall be no coarser than 6,3 pm (Ra). The surface shall exhibit no spiral or longitudinal score marks which could form a leak path.
Where the tubes are not radial to the drum or header shell, there shall be a region of parallel seating in the tube hole at right angles to the axis of the tube. The region shall be at least 13 mm long measured in a plane containing the axis of the tube at the hole;
where tubes are fitted by propulsive expanding, they shall be belled out from the edge of the tube hole at an angle to the tube axis to resist withdrawal. In no such case shall the projection of the tube through the parallel tube seat be less than 6 mm and the belling shall be not less than given in Table 9.4-1.
Table 9.4-1 — Belling dimensions for tubes propulsively expanded
|
Outside diameter of tube mm |
Minimum increase a in diameter of belling over diameter (see Figure 9.4-1) of tube holes rfB mm |
|
d0< 51 |
3 |
|
51 < d0 < 82,5 |
4 |
|
82,5 <d0< 115 |
5 |
Dimensions in millimetres
Key
non-radial hole
seal weld
bell
radial hole with grooves
expansion grooves
radial hole
radial hole without grooves
de tube hole diameter de+a belling over diameter
Figure 9.4-1 —Various typical features relating to tube expansions
Tube to tube mechanical connections
It shall be permissible to join unheated tubes together by mechanical connections or mechanical connections plus seal welding, see EN 12952-3:2011, 11.7 for requirements and limitations.
It shall be not permissible to use mechanical connections to join those portions of tubes together that are to be exposed to furnace radiation or the passage of hot flue gasses.
Connection of non-pressure parts to pressure parts
It shall be permissible to connect non-pressure parts to pressure parts by mechanical means.
NOTE Typical instances are for the support and location of the pressure parts, drum internals, insulation, casing and cladding.
10 Thermal treatment
General
Heating cycles and heat treatment(s) associated with forming operations, other than for the bending of tubes, shall be in accordance with 10.2. The heat treatment requirements associated with the bending of tubes shall be in accordance with 7.3.8 and 7.3.9. Pre-heating shall be in accordance with 10.3. Post weld heat treatment shall be in accordance with 10.4. The heat treatment of production test plates shall be in accordance with 10.5.
Heating cycles and heat treatment(s) associated with plate forming operations
Heating cycles associated with hot forming
The heating cycles applied during hot forming shall be based on the values given in the base material specification or data sheet.
NOTE 1 Other heating cycles may be applied, if in accordance with a qualified procedure approved, and the product is to be tested after forming to demonstrate the adequacy of the material property values in the finished component.
All forming shall be carried out to documented procedures which shall specify, as a minimum, the plate heating rate, the holding temperature, the temperature range and the details of any subsequent heat treatment to be given to the formed part.
NOTE 2 Ferritic steels. Hot forming is a process which is performed in the austenite region. In view of the danger of excessive grain growth, the component should be austenitized at a specified maximum temperature above Ac3, but not higher than 1 020 °С, and after reaching the specified temperature, the component should remain at this temperature for as short a time as possible to avoid grain growth. The heating rate should be as fast as possible e.g. 150 °C/h, through the transition range and, after forming, the component should be allowed to cool freely in still air.
For components made from normalized steels (steel groups 1.1, 1.2 and 2.1), which are formed in a single operation, the maximum temperature of the component shall not be above 980 °С.
For components formed by several operations, the maximum specified temperature of the component shall not exceed 1 020 °С. Before the last operation, the component shall be cooled to below 500 °С, with final heating restricted to a maximum specified of 980 °С for steels with specified minimum yield strengths 7?po,2<355 MPa and 940 °С for steels with specified minimum yield strengths 7?p0,2>355 MPa. If no subsequent heat treatment is to be applied, the last operation of the forming process shall be completed above 750 °С, or above 700 °С where the degree of deformation does not exceed 5 %.
After hot forming under the conditions detailed above, the component shall be allowed to cool in still air.
For components made from quenched and tempered steels, it shall be essential, that a totally new quenching and tempering operation is performed on the whole component after hot forming. For the hot forming itself, the procedures described in 7.3.9.1a) shall apply.
NOTE 3 Austenitic steels. The forming requirements applicable to austenitic steel plates are the subject of development. In the meantime, the methods used in accordance with the manufacturer's own proven procedures ensure that, by their use, the safety of the boiler is not impaired.
Heat treatment associated with forming
The heat treatment required by this European Standard, after hot or cold forming, depends on the requirements of the base material specification or data sheet, and normally be one of the following processes:
normalizing;
normalizing plus tempering;
NOTE Tempering may be part of the stress relieving process of welds, if applicable.
quenching plus tempering;
solution annealing.
Other heat treatment(s) may be applied, if they are in accordance with a qualified procedure, and the product shall be tested after forming to demonstrate the adequacy of the material property values in the finished component.
Shells and strakes
Where a plate is bent to a mean radius less than ten times the plate thickness, it shall be heat treated after bending to the requirements of 10.2.2. However, in the case of materials for which normalizing or normalizing and tempering are the final heat treatments specified in the material specification, or data sheet, the following shall apply:
when the final heat treatment specified is normalizing, provided the component has been heated uniformly to the normalizing temperature during forming, no further heat treatment is required;
when the final heat treatment specified is normalizing and tempering, provided the component has been heat treated uniformly to the normalizing temperature during forming, only additional tempering is required.
Ends
All ends made from plate shall be heat treated after forming to the requirements of 10.2.2. However, in the case of materials for which normalizing or normalizing and tempering are the final heat treatments specified in the material specification, or data sheet, the following shall apply:
when the final heat treatment specified is normalizing, provided the component has been heated uniformly to the normalizing temperature during forming, no further heat treatment is required;
when the final heat treatment specified is normalizing and tempering, provided the component has been heat treated uniformly to the normalizing temperature during forming, only additional tempering is required.
Production test requirements for formed components
Production test coupons shall be provided for hot formed shells, strakes and ends. The number of test coupons required shall be as follows:
shells and strakes - one test coupon per drum. This may, at the manufacturer's risk, be produced as an extension of the weld production test plate, provided that the test plate has been made from the same material as that supplied for the shells or strakes and which has been heat treated with one of the shells or strakes;
ends - one test coupon per heat treatment batch.
The coupons shall be tested to replicate the mechanical tests carried out on the base material by the material supplier.
In the event of a failure of any of the production tests, further testing shall be permitted. This shall be in accordance with the re-testing procedures given in the material specification or data sheet.
Pre-heating for welding and thermal cutting
General
To avoid hard zone cracking in the heat-affected zones of welds and thermally-cut surfaces, consideration shall be given, where appropriate, to the application of pre-heating prior to the commencement of welding, including tack welding, and thermal cutting.
No welding or thermal cutting operations shall be carried out on boiler components when the temperature of the component in the welding or cutting zone is below 5 °С.
NOTE When necessary, staging and protection from the weather is important in order to ensure the welding or thermal cutting operations can be performed under satisfactory working conditions.
Pre-heating for welding
The manufacturer shall include in the welding procedure specification the pre-heating temperatures and, where relevant, the inter-pass temperatures required for the welding. The pre-heat temperature shall be determined by taking into consideration the welding process, the composition and thickness of the metal being welded, the type of joint, the consumable being used and the heat input involved. General recommendations for pre-heating are contained in EN 1011-1:2009.
Where the welding process employed for the root runs differs from that used for subsequent runs, the pre-heating, if any, applicable to each process, shall be determined separately. Any change in pre-heating temperature required, shall be made after the completion of welding by the first process, but before the next process is commenced.
Where the risk of hydrogen cracking exist, e.g. under conditions of severe restraint, consideration shall be given to the benefits of either maintaining or boosting the pre-heat temperature for a minimum of two hours after the welding has been completed, or applying an intermediate post-weld heat treatment to facilitate hydrogen removal.
Where pre-heating is specified, welding, where practicable, shall be continued without interruption. If the continuity of the pre-heating is interrupted, the welding shall be discontinued and the joint shall be allowed to cool slowly by wrapping in a dry insulating blanket. The preheat shall be re-applied before further welding is commenced.
Austenitic steels do not require pre-heat for welding.
No welding or tack welding shall be carried out when the temperature of the parent metal within 150 mm of the joint is less than 5 °С.
Pre-heating for thermal cutting
Pre-heating temperatures for thermal cutting shall be determined by the manufacturer. Recommendations are given in Table 10.3-1.
Table 10.3-1 — Recommended preheat temperatures for thermal cutting
|
Steel type |
Steel group |
Thickness mm |
Minimum preheat temperature °С |
|
C C-Mn |
1.1 |
< 150 > 150 |
Not required 50 |
|
0,3Mo |
1.1 |
< 30 > 30 |
Not required 100 |
|
20MnMoNi |
2.2 |
< 15 > 15 |
Not required 150 |
|
15MnCrMoNiV 15NiMoCuNb |
4.1 4.2 |
< 15 > 15 |
Not required 150 |
|
1 Cr-!4Mo |
5.1 |
<50 > 50 |
Not required 150 |
|
21/дСг-1Мо |
5.2 |
<50 >50 |
100 150 |
|
Cr-Mo-V |
6.2 |
< 50 > 50 |
100 150 |
|
9Cr-1Mo 9Cr-2Mo |
6.4 |
All |
150 |
|
12Cr-1Mo-V |
6.4 |
All |
200 |
|
NOTE The above recommendations should be considered as a general guide to good practice. Other pre-heating temperatures are permitted. |
|||
Measurement of pre-heat
The manufacturer shall implement procedures for the measurement and maintenance of the preheattemperature. Guidance is given in EN ISO 13916:1996.
NOTE Acceptable methods of temperature measurement include temperature-indicating crayons and/or thermo-couples.
The pre-heat temperature shall be checked periodically during the period of application.
Post weld heat treatment
General
The methods of post-weld heat treatment are given in 10.4.2 and post-weld heat treatment procedures are given in 10.4.3. Where, for practical reasons, it is necessary to adopt different methods or procedures, they shall be permitted when:
— the proposed methods or procedures are based on simulation tests on specimens of the material; or
— the methods or procedures are proven by other means as representing safe practice.
The manufacturer shall fulfil the quality requirements for post weld heat treatment according to EN ISO 17663:2009 as appropriate.
The equipment for heat treatment shall be suitable for the heat treatment in question. It shall enable the temperature within the component to be controlled with adequate accuracy and uniformity, especially for those materials which have a small permissible heat treatment temperature range.
Heat treatment records shall be provided which indicate the temperature, the method and rate of heating and cooling, and the holding time. Records shall also be available showing the temperature of martensitic transformation for materials of steel group 6.
Except in the cases covered by 8.8 and 9.4.1, post-weld heat treatment shall be carried out after all welding has been completed.
NOTE In selecting the temperature to be used for heat treatment, the criteria given in Table 10.4-1 should be adopted.
Table 10.4-1 — Criteria for selecting the temperature
|
Method |
Control temperature |
|
Furnace heat treatment |
Use the middle of the specified range. |
|
Non-furnace heat treatment (resistance, induction, controlled flame, etc.) |
Use the upper end of the specified range. |
|
Additional heat treatment (intermediate or repair) |
Use the lower end of the specified range. |
The temperature ranges and holding times used for post-weld heat treatment shall be to the ranges given in Tables 10.4-2 and 10.4-3.
Table 10.4-2 — Temperature ranges for post-weld heat treatment for welded joints of similar and dissimilar materials
|
Steel type |
Steel group |
Temperature range °С |
||||||||||
|
1.1 - 1.4 |
1.1 |
2.2 + 4.1 + 4.2 |
5.1 |
6.1 |
5.2 |
6.2 |
6.4 а |
6.4 а |
||||
|
C-Mn |
1.1 - 1.4 |
550 to 600 |
550 to 600 |
550 to 600 |
|
|
|
|
|
|
||
|
0,3Mo |
1.1 |
|
550 to 630 |
550 to 600 |
600 to 630 |
|
|
|
|
|
||
|
20MnMoNi 15MnCrMoNiV 15NiMoCuNb |
2.2 4.1 4.2 |
|
|
570 to 620 |
600 to 620 |
|
|
|
|
|
||
|
1Cr1/2Mod |
5.1 |
|
|
|
620 to 680 |
650 to 690 |
650 to 700 |
|
|
|
||
|
14MoV |
6.1 |
|
|
|
|
680 to 730 |
690 to 730 |
|
|
|
||
|
27«Cr1 Mo' |
5.2 |
|
|
|
|
|
680 to 730 |
730 to 750 |
730 to 760 710 to 730 b |
|
||
|
Cr-Mo-Vc |
6.2 |
|
|
|
|
|
|
720 to 760 |
740 to 760 |
740 to 760 |
||
|
9Cr1Mo 9Cr2Mo |
6.4 a |
|
|
|
|
|
|
|
740 to 780 |
740 to 770 |
||
|
12Cr1Mo-V |
6.4 a |
|
|
|
|
|
|
|
|
730 to 770 |
||
