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This standard is modified in relation to DL/T 905-2004 Technical guide for repair welding of turbine blades in accordance with the Notice on issuing the development and revision plan of the second batch of professional standards of energy sector in 2013 (GUONENGKEJI [2013] No.526) issued by the National Energy Administration of the People's Republic of China.
This standard is prepared in accordance with the rules given in GB/T 1.1-2009 Directives for standardization—Part 1: Structure and drafting of standards.
This standard replaces DL/T 905-2004 Technical guide for repair welding of turbine blades. In addition to a number of editorial changes, the following technical changes have been made with respect to DL/T 905-2004:
——The application scope of the standard has been expanded, and the content of repair welding for hydroturbine runner has been added;
——The requirements for baking welding rod have been added;
——The requirements for wind speed and humidity in welding environment have been added;
——The requirements for monitoring preheating temperature before repair welding for blade of steam turbine have been added;
——The requirements for background current and peak current of pulsed argon tungsten-arc welding have been added;
——The requirements for repair process for hydroturbine runner have been added;
——The requirements for ultrasonic testing after repairing hydroturbine runner have been added;
——The requirements for the purity of argon gas have been modified;
——The requirements for grinding base metal before fitting up blades for welding have been modified，and the range of base metal to be ground has been specified;
——The requirements for welding materials, preheating and interlayer temperature and post-welding heat treatment recommended for repairing blade of steam turbine have been modified;
——The requirements for welding process during repair welding for blade of steam turbine have been modified.
This standard was proposed by the China Electricity Council (CEC).
This standard is under the jurisdiction of the Technical Committee on Power Station Welding of Standardization Administration of Power Industry.
This standard was firstly issued in 2004, and this edition is the first revision.
This standard replaces DL/T 905-2004 Technical guide for repair welding of turbine blades from the implementation date hereof.
Any comments or suggestions during the implementation of this standard may be fed back to the Standardization Center of the China Electricity Council (No.1, 2nd Lane, Baiguang Road, Beijing, 100761, China).
Code of repair welding for blade of steam turbine and runner of hydroturbine
1 Scope
This standard specifies the technical conditions and inspection requirements for repair welding for blades of steam turbine and runners of hydroturbine.
This standard is applicable to the repair welding of steam turbine blades, blade shrouds and lacing wires in fossil-fuel power plants, and the repair welding of hydroturbine runners in hydropower plants.
2 Normative references
The following referenced documents are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 3323 Radiographic examination of fusion welded joints in metallic materials
GB/T 11345 Non-destructive testing of welds—Ultrasonic testing—Techniques, testing levels, and assessment
GB/T 29712 Non-destructive testing of welds—Ultrasonic testing—Acceptance levels
DL/T 438 The technical supervision codes for metal in fossil-fuel power plant
DL/T 675 Examination codes for qualification of non-destructive testing personal of electric power industry
DL/T 679 Code for welder technical qualification
DL/T 819 The code of the welding heat treatment for power plant
DL/T 868 Qualification standard for welding procedures
DL/T 869 The code of welding for power plant
DL/T 1318 Technical supervision code for hydroelectric power plant metals
JB/T 3223 Welding consumables quality management procedures
NB/T 47013.4 Nondestructive testing of pressure equipment—Part 4: Magnetic particle testing
NB/T 47013.5 Nondestructive testing of pressure equipment—Part 5: Penetrant testing
SJ/T 10743 Ceriated tungsten electrodes for inert gas arc welding and plasma welding and cutting
3 General rules
3.1 Welding personnel
3.1.1 General requirements
Welding personnel include welding technicians, welders, welding heat treatment personnel and inspectors. All types of personnel shall meet the provisions of this standard in addition to the relevant requirements of DL/T 869.
3.1.2 Welding technicians
3.1.2.1 Welding technicians shall be technicians from the welding major or similar majors with the title of engineer or above, and shall be in charge of the welding process test and the repair welding for blade of steam turbine and runner of hydroturbine.
3.1.2.2 Welding technicians shall know the operating conditions of the parts to be repaired and the causes of defects, master the welding performance of the materials of the parts to be repaired, and be acquainted with and conscientiously implement this standard.
3.1.2.3 Welding technicians are responsible for determining the inspection position, recording, checking and sorting out the welding data and compiling the technical summary.
3.1.3 Welders
3.1.3.1 Welders shall be qualified as Class I welders as specified in DL/T 679 or as approved by the owner.
3.1.3.2 Before welding, welders shall practice welding according to the operation instruction by simulating the actual onsite situation using the parts of the same materials and types as those to be repaired. During welding, welders shall strictly abide by the welding process plan or operation instruction, and report problems, if any, to the welding technicians in time (handling without permission is prohibited).
3.1.4 Welding heat treatment personnel
3.1.4.1 Welding heat treatment personnel shall perform duties in accordance with the requirements of DL/T 819.
3.1.4.2 Welding heat treatment personnel shall strictly implement the requirements for welding heat treatment in the welding process plan or operation instruction, and timely sort out and summarize welding heat treatment data.
3.1.5 Welding inspectors
3.1.5.1 Welding inspectors include non-destructive inspectors and physical and chemical inspectors.
3.1.5.2 Non-destructive inspectors shall have an inspection qualification of Class II or above specified in DL/T 675 or issued by other institutions, record the original defects of the parts to be repaired before welding, inspect the repaired parts, and issue the inspection report in time.
3.1.5.3 Physical and chemical inspectors shall carry out inspection according to the requirements of this standard and the welding process plan, and issue the inspection report in time.
3.2 Welding process test
3.2.1 Before welding, welding process tests shall be carried out applying corresponding performance requirements and welding process to be adopted for the parts to be repaired, and the test results shall be qualified.
3.2.2 Simulated welding test, destructive test or other tests specified in DL/T 868 may be carried out when necessary.
3.2.3 The welding process plan or operation instruction shall be prepared on the basis of the process test result and the actual situation.
3.3 Welding materials and management
3.3.1 Welding materials to be used shall be provided with quality certificate issued by the manufacturing plant. The storage and usage management of welding materials shall comply with the rules of JB/T 3223, and when necessary, welding materials shall be re-inspected and only those qualified can be used.
3.3.2 The welding materials used shall meet the requirements of corresponding standards. Ceriated tungsten electrode or lanthanated tungsten electrode shall be used in argon tungsten-arc welding. Ceriated tungsten electrode used shall meet the requirements of SJ/T 10743, and the purity of argon gas used shall be 99.99% or above.
3.3.3 Welding rods shall be baked in accordance with the requirements of the instructions before use. Do not re-bake the welding rod more than twice. For the convenience of usage, put the welding rod in a dedicated insulation barrel of 80°C~110°C.
3.4 Equipment for repair welding
3.4.1 Welding equipment, carbon arc gouging equipment, welding heat treatment equipment, welding rod drying equipment, physical and chemical inspection equipment and non-destructive testing instruments shall be safe and reliable with stable parameters and flexible adjustability, meeting the corresponding technical requirements.
3.4.2 Use DC welding power supply with functions of automatic arc-ignition and automatic arc-extinguishing by attenuation. DC power supply with pulse function should be selected for manual argon tungsten-arc welding and gas-shielded welding.
3.4.3 Where there are metrological verification requirements, the equipment shall be in the validity period of the verification.
3.5 Safety requirements and environment conditions
3.5.1 Welding operation shall comply with the relevant rules of safety.
3.5.2 The ambient temperature for welding operation shall not be lower than 5°C. The ambient wind speed for gas-shielded welding shall not be more than 2 m/s, and that for other welding methods shall not be more than 8 m/s. The relative ambient humidity shall not be more than 80%.
4 Preparation before repair welding
4.1 Confirmation of material and determination of defect location
4.1.1 Before repair, the chemical composition and properties of the base metal of the parts to be repaired shall be confirmed on the basis of manufacturing drawings or other technical documents provided by the manufacturing plant. Sample the metal base for chemical composition analysis when necessary.
4.1.2 Before repair, check the distribution and size of defects, determine the types of defects and make records. Ultrasonic testing, magnetic particle testing or penetrant testing should be adopted during checking.
4.1.3 If the welding process test result shows that the performance after repair fails to meet the requirements, the repair welding for blade of steam turbine and runner of hydroturbine shall not be carried out. When the crack defect is within 2/3 of the length from the blade root to the blade tip, the repair welding for blade of steam turbine should not be carried out.
4.2 Removal of defects
4.2.1 Superficial defects shall be removed by mechanical means.
4.2.2 To remove crack defects on hydroturbine runner, mechanical means or carbon arc gouging may be adopted. When using carbon arc gouging method to remove the crack, it is necessary to preheat the defect area to the temperature suitable for the material of the parts to be repaired. It is suggested to mark at a position 1 mm away from the crack tip and open a crack arrest hole there before remove the crack from the crack tip. After gouging, the carburized layer shall be polished until metallic luster is revealed.
4.2.3 For repairable steam turbine blades, defects shall be removed by mechanical means. If there is Stellite alloy sheet or other corrosion-proof alloy layer on the back of the blade, the alloy sheet or layer at the crack shall be cleaned before removal of defect.
4.2.4 After the defect is removed, an inspection shall be carried out to confirm that the defect has been eliminated.
4.3 Groove and fitting
4.3.1 When fitting broken blades, special clamp shall be used, and there shall not be misalignment and bending.
4.3.2 When there are penetrating cracks, double-sided grooves should be adopted. The groove angle and fitting clearance shall be determined according to the thickness of the blades on the principles of easy operation, full welding and minimized filling.
4.3.3 The materials selected for repair should match the original materials, and pass the physical and chemical inspection. Before fitting, the line shape of the blade shall be processed in advance until it is basically consistent with the original blade, and a certain machining allowance shall be left.
4.3.4 Before fitting, the groove and the base metal within 20 mm to the groove shall be polished until metallic luster is revealed.
4.3.5 The power supply ground wire used for welding shall be directly connected with the welded parts, firmly clamped and in good contact. Do not connect the ground wire to the bracket of the rotor.
5 Repair welding process
5.1 Repair welding process for steam turbine blade
5.1.1 Welding method
Argon tungsten-arc welding is preferred, and shielded metal arc welding may also be used.
5.1.2 Welding materials
5.1.2.1 Welding materials shall match blade materials. Under special circumstances, iron-based or nickel-based austenitic heterogeneous welding materials may be used.
5.1.2.2 See Table 1 for welding materials and welding heat treatment process recommended for repairing blade of steam turbine. To use special welding materials, welding process test of these materials shall be carried out, and the test result shall meet the design requirements.
Table 1 Welding materials and welding heat treatment process recommended for repairing blade of steam turbine
Blade material Welding wire model Welding rod model Preheating and interlayer temperature
(°C) Post-weld heat treatment
Temperature
(°C) Heat preservation time
(h)
12Cr13, 20Cr13 H12Cr13 E410 -15 200~250 680~720 0.5
H08Cr19Ni10Ti
H08Cr20Ni10Nb E347 -15 100~150
12Cr02Mo H08Cr19Ni10Ti
H08Cr20Ni10Nb E410 -15 100~150 680~720 0.5
05Cr17Ni4Cu4Nb H00Cr17Ni4Cu4Nb — 100~150 600~650 0.5
5.1.3 Preheating and interlayer temperature
5.1.3.1 The resistance-heating method should be adopted during preheating. The heating width, heat preservation and temperature measurement shall comply with the relevant rules of DL/T 819.
5.1.3.2 When preheating with oxygen-acetylene neutral flame, the preheating range is 50 mm on both sides of the groove. When preheating, the flame core shall be 10 mm or further away from the workpiece. The heating shall be even. It is recommended to monitor the preheating temperature at the position 50 mm away from the edge of the groove by a far infrared thermometer or other non-contact temperature measurement methods.
5.1.3.3 When measuring temperature by thermocouple, it is forbidden to fix the thermocouple by welding (including welding with an energy storage welder).
5.1.3.4 Recommended preheating and interlayer temperatures are shown in Table 1.
5.1.4 Welding position and welding sequence
5.1 4.1 The welding position shall be as horizontal as possible.
5.1.4.2 For blades broken completely, weld from the thick side to the thin side. For unbroken blades, weld from the inner side to the edge of the blade. For the thin edge of the blade, welder may adopt the welding process by welding on one side of the groove, by which welds will be formed on both sides of the groove.
5.1.5 Welding process
5.1.5.1 The recommended argon tungsten-arc welding process is as follows:
a) The welding wire with diameter less than or equal to 2.0 mm should be selected, and the recommended welding current is 50 A ~ 70 A. The background current of pulsed argon tungsten-arc welding is 30 A ~ 50 A, and the peak current is 90 A ~ 110 A.
b) During welding, the weld shall be provided with delayed protection, and the back of the weld shall be treated with argon-filled protection.
c) Multi-layer and multi-pass welding should be used.
d) The weld reinforcement after welding shall be controlled within 1 mm.
5.1.5.2 The recommended shielded metal arc welding process is as follows:
a) The welding rod with diameter less than or equal to 2.5 mm should be selected, and the recommended welding current is 60 A ~ 90 A.
b) Multi-layer and multi-pass welding should be adopted. The width of the weld bead shall not exceed 3 times of the diameter of the welding rod, and the thickness shall not exceed 3 mm.
c) During double-sided welding, gouge the root.
d) The weld reinforcement after welding shall be controlled around 1 mm.
5.1.6 Post-weld heat treatment
5.1.6.1 After welding, the blades shall be coated and cooled slowly in time, and post-weld heat treatment shall be carried out immediately when the temperature of the weld core drops to about 100 °C.
5.1.6.2 Resistance-heating should be used for post-weld heat treatment, and the blade should be in the vertical position as much as possible during heat treatment.
5.1.6.3 The hot end of the thermocouple shall be close to the center of the weld, but the thermocouple shall not be fixed by welding (including welding with an energy storage welder).
5.1.6.4 The heating width is 30 mm ~ 60 mm on each side of the weld.
5.1.6.5 During heat treatment, remove the heater and thermal insulation device after the time for heat treatment is over, and let the blade be air-cooled.
Foreword i
1 Scope
2 Normative references
3 General rules
3.1 Welding personnel
3.2 Welding process test
3.3 Welding materials and management
3.4 Equipment for repair welding
3.5 Safety requirements and environment conditions
4 Preparation before repair welding
4.1 Confirmation of material and determination of defect location
4.2 Removal of defects
4.3 Groove and fitting
5 Repair welding process
5.1 Repair welding process for steam turbine blade
5.2 Repair process for hydroturbine runner
6 Quality inspection
6.1 Inspection contents
6.2 Appearance inspection
6.3 Non-destructive testing
6.4 Hardness and metallographic inspection
6.5 Others
7 Weld repair
8 Technical documents
