ORBITAL WELDING AN EXPERIENCE AT KKNPP

PLANT CAPACITY – 2 X 1000 MWe 3 Nos. per unit STEAM TURBINE 1 HPC + 3 LPC 3 Nos. per unit CONDENSER TITANIUM TUBES Size 25 X 0.6mm 15 meters long 90000 Nos.

Process – GTAW without filler wire addition ORBITAL WELDING 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 Material supply 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)

Titanium tube insertion 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

Final expansion 8 to 10 % by lubricating SAE 40 oil 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

Final cleaning by acetone 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)

TUBE SPECIFICATION

UNIT-2 TUBE INSERTION

AFTER TUBE INSERTION

TUBE SHEET PROTECTION

FRONIUS MODEL - FPA 2000 (AUSTRIAN MAKE) PROGRAMABLE ORBITAL WELDING MACHINES FRONIUS MODEL - FPA 2000 (AUSTRIAN MAKE)

Welding parameters for FRONIUS MODEL - FPA 2000 Process : GTAW (Automatic ) No of weld passes 1 Argon 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

PROGRAMABLE ORBITAL WELDING MACHINES VJ MARCONS - HYDERABAD (Indian Make)

WELDING PARAMETERS FOR VJ MARCONS HYDERABAD Name of the weld programme :KK1 No of weld passes : 1 Aux Gas shield required : Yes Torch shield gas delay, Sec :10 Pre gas time, sec : 3.0 Overlap required, mm :8.0 Up slope time, sec : 2.0 Pre heating time, sec : 1.0 Down slope time, sec : 5.0 Post weld gas flow time, sec :3.0 Aux Gas turn off delay, sec :5.0 Pulse welding : Yes Peak 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 & 005 PQR: BHEL/KKNPP/PQR/004 & 005 Welding Process: Automatic TIG Welding with out filler material addition 7 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

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

TYPE OF WELD DEFECTS Defective Shape Surface pores Burn Through-Minor 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

RECTIFICATION USING Ti DISC 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

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