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ORBITAL WELDING
AN EXPERIENCE AT KKNPP
AN EXPERIENCE AT KKNPP
PLANT CAPACITY – 2 X 1000 MWe
STEAM TURBINE 1 HPC + 3 LPC
CONDENSER 3 Nos. per unit
TITANIUM TUBES Size 25 X 0.6mm 15 meters long 90000 Nos.
ORBITAL WELDINGPurpose – To provide leak proof joint between Tube to tube sheet in
Condenser in addition to Forced expansion
Process – GTAW without filler wire addition
Material-Titanium
Large Qty of welding
Welding in position & at site
Material supply by Russians
SIGNIFICANT ASPECTS
TITANIUM TUBES
Grade : ASTM B 338 Gr2
Tube Sheet : 35 + 5 mm thick
Material : ASTM A516Gr 70 + ASTM B 265 Gr 1
CLADWhy Titanium is used?
Provides excellent resistance to general and localized attack under most oxidizing, neutral and inhibited reducing conditions in aqueous environments.
Titanium Cont….
Corrosion Resistance due to stable, protective strongly adherent oxide film which forms instantly when a fresh surface is exposed to air moisture.
This film is transparent and not deducted by visual means.
Titanium resist corrosion by sea water to temperature as high as 260 0 C.
Even exposed to sea water for many years at a depth of over a mile shows no measurable corrosion.
Titanium Cont….
Provides over 25 years of trouble free sea water service for chemical refinery de-salination and nuclear industries
Has the ability to resist erosion by high velocity sea water
The presence of abrasive particles such as sand has only a small effect on the corrosion resistance of Titanium
Production began in the late 1950s
Most widely used titanium is commercial pure (99.5 % Ti)
Manufacturing Process
Ingot →slab → Hot strip → cold strip → Slitting → Forming → TIG Welding → Stress relieving → Eddy Current & Ultrasonic testing
Tensile, flare, flattening & reverse flattening
Visual InspectionCleanliness, ID, OD, Surface condition, end condition and marking.
Tube to tube sheet joining
Contact Rolling (0 to 5 % wall thinning for a length of 10 mm)
Orbital Welding – For highly reliable leak tightnessForced Rolling (8 to 10 % wall thinning for a length of 25mm)
Physical Testing
PROCESS FLOW CHARTFront / Rear end tube sheet cleaning – wire brush mounted in portable drilling machine
followed by acetone
Visual inspection
Titanium tube insertion
Initial cleaning before contact rolling
Initial contact rolling up to 10mm
Sh 1 of 3
End facing of tube & tube sheet up to 0.05 mm
Welding
Visual inspection
Rectification of repair work
Final expansion 8 to 10 % by lubricating SAE 40 oil
Excess length trimming in the rear side
PROCESS FLOW CHART CONTD…Sh 2 of 3
Tube tightness test by MAUS Gun G-150
Dye Penetrant testing
Final cleaning by acetone
PROCESS FLOW CHART CONTD… Sh 3 of 3
RUSSIAN REFERENCE DOCUMENTS
GOST 3242 – 79 Welding joints Quality Control Methods
RD 24.020.00-93 (Guide lines welding joints of mixed steam, gas and Hydraulic Turbines)
PNAEG 7-003-87 Welder qualification
PNAEG 7-010-089 Acceptance standard
WORK PROCEDURES
Condenser Tubing and expansion(Doc.No: BHEL / KKNPP / WP / 023)
Condenser Tube Welding (Doc.No: BHEL / KKNPP / WP / 024)
Condenser Tube to Tube sheet welding repair procedure (Doc.No: BHEL / KKNPP / WP / 031)
TUBE SPECIFICATION
UNIT-2 TUBE INSERTION
AFTER TUBE INSERTION
TUBE SHEET PROTECTION
FRONIUS MODEL - FPA 2000 (AUSTRIAN MAKE)
PROGRAMABLE ORBITAL WELDING MACHINES
Welding parameters for FRONIUS MODEL - FPA 2000
Process : GTAW (Automatic )
No of weld passes 1Argon Gas flow rate 4 to 6 ltr /min
Pre Gas time T10 30 Sec Post Gas time T11 30 Sec Pre Fusion current I21 90A Pre fusion current time T21 0.1Sec Pulse current I22 90A Time of pulse current T22 100msec
Welding parameters for FRONIUS MODEL - FPA 2000 (Cont…)
Back ground current I23 40A
Time of back ground current T23 100 m sec Down slope state N20 365D
Down slope time T25 5 Sec
Welding Speed V 32 = 125%
Tungsten electrode:
Grade- WL10
Diameter- 1.6 mm
Inclined Angle – 2 0
Grinding Angle – 15 0
VJ MARCONS - HYDERABAD (Indian Make)
PROGRAMABLE ORBITAL WELDING MACHINES
WELDING PARAMETERS FOR VJ MARCONS HYDERABAD
Name of the weld programme :KK1No of weld passes : 1Aux Gas shield required : YesTorch shield gas delay, Sec :10Pre gas time, sec : 3.0Overlap required, mm :8.0Up slope time, sec : 2.0Pre heating time, sec : 1.0Down slope time, sec : 5.0Post weld gas flow time, sec :3.0Aux Gas turn off delay, sec :5.0Pulse welding : YesPeak Current, amps : 90.0
WELDING PARAMETERS FOR VJ MARCONS HYDERABAD (Cont…)
Base Current, amps : 20.0
Peak time, sec : 0.1
Base time, sec : 0.1
Welding speed, RPM : 2.0
Diameter of the tube, mm : 25
WPS AND PQR
Welding Process: Automatic TIG Welding with out filler material addition7 Welds Per Machine Per Operator
NDT – Visual (Uniform contour free from spatter, burn-through, cracks, surface pores etc.
WPS: BHEL/KKNPP/WPS/004 & 005PQR: BHEL/KKNPP/PQR/004 & 005
Weld spillage, undercut, weld color, DPT etc.
Destructive Testing
Metallographic Examination – Minimum leak path, Weld width and height.
METALLOGRAPHIC TESTING• Sample ID: 2• Measurement of individual inclusions and clusters as per Table .19 of
PNAEG-07-010-89 of 11.11 metallographic analysis:• L = 0.622 mm• No. of inclusions present – Nil• • a =0.620 mm• h=1.02 mm• H=1.39 mm• W=3.48 mm
• • Mag: 10x Etchant:5%HF• Calculation of Minimum Leak Path (L) = a + Σdp > 0.7t• dp = d1 + d2 where d = dia of the pore• t = Thickness of the tube = 0.6mm• L = 0.622• a = 0.620
W=3.48 mm
H=1.39 mm
h=1.02 mm
MACHINE & OPERATOR QUALIFICATIONWELDING MACHINES:
• FRONIUS MODEL - FPA 2000 - 4 Nos• VJ MARCONS - HYDERABAD - 2 Nos
CONTACT & FORCED ROLLING MACHINES
CONTACT ROLLING SUGINO 502 L - 2 NosFORCED ROLLING SUGINO 506 L - 3 Nos
OPERATORS
WELDERS - 15CONTACT ROLLING - 5FORCED ROLLING - 4
TUBE TO TUBE SHEET WELDING
WELDING HISTORY
Start of welding in Unit-1 :29-03-06
Completion in Unit-2 : 30.11.07
Average out put
FRONIUS MODEL - FPA 2000 : 250 Joints/Shift/Machine
VJ MARCONS - HYDERABAD :200 Joints/Shift/Machine
TUBE TIGHTNESS CHECK BY MAUS GUN G-150
Compressed Air System Pressure 3 to 9 Bar
Air flow rate 30 l/min
Test pressure holding time 5 to10 sec
CLEAN ROOM
WATER BOX
TYPE OF WELD DEFECTS
Transverse Cracks Color Change
Blow Holes Pores
Surface pores
TYPE OF WELD DEFECTS
Defective Shape
Burn Through-Major Burn Through-Minor
WELD DEFECTS RECTIFICATION
Efforts to change the acceptance norm-2 Letters
Repair – by machine or manual
Manual-Filler wire (Russian), ASTM
-Color change (Gas lens), Trailing shield
-Trailing shield (Half circle, Rectangle)
-Qualification requirement
-Creation of defects
-welder availability
Welding Accessories
Heat Sink
Manual Welding
Trailing Shield
CRITICAL WELD DEFECTS
RECTIFICATION USING Ti DISC
MOCK UP BLOCK WITH CRATED CRACKS
PULSE TIG MACHINE
Ti DISC WITH HOLDER
Ti DISC FIXING
DRILLING
FINISHED HOLES
FINISHED HOLES
ESSENTIALS FOR GOOD WELD JOINT
Joint preparation-Paint removal, cleanliness, end facing
Clean room environment
Process parameters, Welding machine, Operators
Parent material & Cladding Quality
Heat in put & Post expansion control
Titanium is a Royal material and one does not learn unless burn his finger
THANK YOU