ORBITALWELDING AN EXPERIENCE AT KKNPP
PLANT CAPACITY – 2 X 1000 MWe STEAM TURBINE 1 HPC + 3 LPC 3 Nos. per unit CONDENSER TITANIUM TUBES Size 25 X 0.6mm 15 meters long 90000 Nos.
ORBITALWELDING Purpose – To provide leak proof joint between Tube to tube sheet in Condenser in addition to Forced expansion Process – GTAW without filler wire addition SIGNIFICANT ASPECTS Material-Titanium Large Qty of welding Welding in position & at site Materialsupply by Russians
TITANIUM TUBES Grade:ASTM B 338 Gr2 Tube Sheet : 35 + 5 mm thick Material : ASTM A516Gr 70 + ASTM B 265 Gr 1 CLAD Why 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
Physical Testing Tensile, flare, flattening & reverse flattening Visual Inspection Cleanliness, 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 tightness Forced Rolling (8 to 10 % wall thinning for a length of 25mm)
PROCESS FLOW CHART Sh 1 of 3 Front / 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
PROCESS FLOW CHART CONTD… Sh 2 of 3 End facing of tube & tube sheet up to 0.05 mm Welding Excess length trimming in the rear side Visual inspection Rectification of repair work Final expansion 8 to 10 % by lubricating SAE 40 oil
PROCESS FLOW CHART CONTD… Sh 3 of 3 Final cleaning by acetone Dye Penetrant testing Tube tightness test by MAUS Gun G-150
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)
PROGRAMABLE ORBITAL WELDING MACHINES FRONIUS MODEL - FPA 2000 (AUSTRIAN MAKE)
Welding parameters for FRONIUS MODEL - FPA 2000 Process : GTAW (Automatic )No of weld passes 1Argon Gas flow rate 4 to 6 ltr /minPre Gas time T10 30 SecPost Gas time T11 30 SecPre Fusion current I21 90APre fusion current time T21 0.1SecPulse current I22 90ATime 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
PROGRAMABLE ORBITAL WELDING MACHINES VJ MARCONS - HYDERABAD (Indian Make)
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 WPS: BHEL/KKNPP/WPS/004 & 005PQR: BHEL/KKNPP/PQR/004 & 005 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. 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 QUALIFICATION WELDING MACHINES: • FRONIUS MODEL - FPA 2000 - 4 Nos • VJ MARCONS - HYDERABAD - 2 Nos CONTACT & FORCED ROLLING MACHINES CONTACT ROLLING SUGINO 502 L - 2 Nos FORCED ROLLING SUGINO 506 L - 3 Nos OPERATORS WELDERS - 15 CONTACT ROLLING - 5 FORCED ROLLING - 4
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
Transverse Cracks Color Change Pores Blow Holes TYPE OF WELD DEFECTS
Surface pores Defective Shape Burn Through-Minor Burn Through-Major TYPE OF WELD DEFECTS
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
CRITICAL WELD DEFECTS RECTIFICATION USING Ti DISC
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