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