Welding Methods – Indian Railways Perspective

1. Why Welding Matters on Railways

• 94 % of Indian Railways’ 68,000 route-km is welded track (LWR/CWR) → eliminates fish-plated joints, reduces maintenance & ride noise.
• Welded turnouts, bridges, wagons & coaches → 30 % lighter, 40 % stronger than riveted structures.
• Welding defects → cause 17 % of rail fractures (Railway Board Safety Report 2022) → hence welding is a Category-A skill for JE/ALP/Technician.

2. Rail Steel Chemistry (to be welded)

High carbon & alloy → hardenability & crack sensitivity → governs welding procedure.

3. Classification of Welding Processes used on IR

A. Fusion Welding (melts base metal)

1. Gas Pressure Welding (GPW) – Thermit® process (Alumino-thermic)
2. Electric Arc Welding
   • SMAW (Manual Metal Arc) – electrodes: AWS E11018-M
   • GMAW (MIG/MAG) – ER90S-G wire, Ar+20 % CO₂
   • FCAW – AWS E91T1-K2
   • SAW – Submerged Arc (turnouts, bridges)
3. Flash-Butt Welding (FBW) – mobile & fixed plants
4. Electro-slag / Electro-gas – thick web crossings
5. Laser, Plasma, EBW – Metro & LHB coach body (stainless steel)

B. Solid-State Welding (no melt)

1. Friction Welding – Alstom LHB wheel-axle
2. Explosive Welding – transition joints for aluminium roof to steel body

4. Thermit (Gas Pressure) Welding – Most Asked in Exams

• Invented 1895 – Hans Goldschmidt – first rail weld 1899 in Germany; India 1928 on GIPR.
• Reaction:
  3 Fe₃O₄ + 8 Al → 9 Fe + 4 Al₂O₃ + 3.2 MJ kg⁻¹ (Temp ≈ 2,400 °C)
• Standard portion: 450 g Fe₃O₄ + 90 g Al + 15 g Ni & Cr = One crucible for 60 kg rail.
• Pre-heat temp: 900–1,000 °C (cherry red) – measured by optical pyrometer or Tempilstik° 980.
• Gap kept: 25 mm ± 1 mm (Indian Railways Permanent Way Manual 2021).
• Alignment tolerance: vertical ≤ 0.5 mm, lateral ≤ 0.3 mm.
• Upset metal (weld collar) projection: 3–5 mm each side.
• Cooling: 6 min natural + 10 min sand covering → only then traffic at 10 km/h; full speed after 1 h/30 °C temp fall.
• Acceptance test:
  • USFD 100 % (2 MHz probe)
  • Transverse tensile ≥ 720 MPa
  • Bend 120° on 1.5 m mandrel without crack
  • Hardness survey ≤ 350 HV in HAZ
• Defect rate target: ≤ 2 % (RB’s “Zero-Weld-Failure” drive 2023).

Recent IR initiative

• Auto-Thermit kit (RDSO 2017) – crucible pre-loaded, exothermic start by remote → reduces fume exposure to welders.
• Green-thermit – 30 % lower Al, Fe₃O₄ sourced from spent mill-scale → saves 1.2 t CO₂ per 1,000 welds.

5. Flash-Butt Welding (FBW) – Factory & SFW Pads

• Kaiser’s 1924 patent; Indian Railways first plant 1963 at Bhilai Steel Plant.
• Principle: Joule heating I²Rt + forging upset 6–8 mm.
• Parameters for 60 kg rail (UIC-60):
  • Flash voltage: 3–6 V
  • Current: 55–65 kA
  • Upset force: 450 kN
  • Total cycle: 120–150 s
• Heat-affected zone (HAZ) width: 25–30 mm (half of Thermit).
• Standards: IRS-T-18-2019 (provisional) & EN 14587-2.
• NRC (Greenfield) & RRTS “KAVACH” corridors: 100 % FBW rails.
• Mobile Flash-Butt Welding Plant (RDSO 2022) – 25 t self-propelled – can do 60 welds/day on running track → reduces possession time by 70 %.

6. SMAW & GMAW for Rolling Stock

• Electrode for freight wagon (IRSM-44 steel): AWS E7018 (4 mm Ø) – 160 A DC+.
• LHB coach shell (Stainless steel 301LN): GMAW-Short Circuit, 1.2 mm ER308LSi, 24 V, 180 A, 60 % Ar + 30 % He + 10 % CO₂.
• WPS qualified as per IS 7310 Part 1 & AWS D1.1/D1.6.
• Welder certification: BIS-5284 (earlier CITI) – valid 2 years, 6-month renewal test.

7. Defects, Symbols & NDT

8. Safety & Environmental Stats

• IR employs ~22,000 certified welders (2023).
• “Weld-Cloud” app (CRIS 2021) – geo-tagged every Thermit weld, uploads temp & USFD report → failure-analysis database.
• Hex-Chrome exposure limit (GMAW on SS): 0.05 mg m⁻³ (Factories Act 2020).
• Fire risk: Thermit crucible temp > 2,000 °C – mandatorily carried out in “Weld-Zone” 5 m clear of timber sleepers; water buckets & 2 DCP extinguishers kept.

9. Historical Timeline (Memory tip)

• 1895 – Goldschmidt invents Thermit
• 1928 – First Indian rail weld (GIPR)
• 1963 – Bhilai FBW plant
• 1998 – LWR made mandatory on BG
• 2010 – RDSO approves SKV-E (improved) mould
• 2017 – Auto-Thermit kit
• 2020 – Mobile FBW plant trials
• 2022 – RDSO permits “Wide-gap Thermit” (up to 60 mm gap) for repair

10. Future / Recent Updates (2023-24)

• “Friction-Stir Welding” of 6061-T6 aluminium roof panels – successful trial at Rail Coach Factory, Kapurthala – 40 % joint strength ↑, no fumes.
• “RailBot-W” – under development by DMRL & IR – AI-guided “narrow-gap laser-MAG hybrid” for field welds; expected 2026.
• Green-Hydrogen instead of Acetylene for gas pre-heating (IROAF pilot) → 2.5 kg CO₂ saved per weld.

15+ Railway-Exam MCQs on Welding Methods

1. Which reaction mixture is used in Thermit welding of rails? A) Fe₂O₃ + Al B) Fe₃O₄ + Al C) FeO + Al D) Fe + Al₂O₃

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   Correct Answer: B Explanation: The reaction mixture used in Thermit welding of rails typically consists of Iron Oxide (Fe₃O₄) and Aluminum (Al) powder.

2. The pre-heating temperature required before pouring Thermit metal is about A) 600–700 °C B) 700–800 °C C) 900–1,000 °C D) 1,100–1,200 °C

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   Correct Answer: C Explanation: Rail ends must be pre-heated to approximately 900–1,000 °C to ensure proper fusion with the molten Thermit steel.

3. Standard gap kept between rail ends during Thermit welding is A) 25 mm ± 1 mm B) 20 mm ± 1 mm C) 30 mm ± 1 mm D) 15 mm ± 1 mm

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   Correct Answer: A Explanation: A standard gap of 25 mm ± 1 mm is maintained to allow the molten metal to flow and fuse the rail ends effectively.

4. Which welding process gives the smallest HAZ (Heat Affected Zone) width on rails? A) Thermit Welding B) Gas Pressure Welding C) Arc Welding D) Flash-Butt Welding

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   Correct Answer: D Explanation: Flash-Butt Welding uses intense localized heating and pressure, resulting in the narrowest Heat Affected Zone compared to other methods.

5. The first rail weld in Indian Railways was carried out in the year A) 1910 B) 1928 C) 1947 D) 1952

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   Correct Answer: B Explanation: History records the first instance of rail welding on the Indian Railway system in 1928.

6. Current required for Flash-Butt welding of 60 kg UIC rail is approximately A) 25–35 kA B) 40–50 kA C) 55–65 kA D) 70–80 kA

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   Correct Answer: C Explanation: To achieve the necessary heat for a 60 kg UIC rail section, a high current in the range of 55–65 kA is required.

7. Which electrode is recommended for welding IRSM-44 freight wagon underframe? A) AWS E7018 B) AWS E6013 C) AWS E6011 D) AWS E8018

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   Correct Answer: A Explanation: AWS E7018 is a low-hydrogen carbon steel electrode commonly used for high-quality structural welding in railway wagons.

8. The minimum transverse tensile strength accepted for a Thermit weld joint is A) 600 MPa B) 720 MPa C) 850 MPa D) 900 MPa

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   Correct Answer: B Explanation: As per standard specifications, a Thermit weld must exhibit a minimum transverse tensile strength of 720 MPa.

9. Which NDT technique is mandatory for 100 % inspection of field Thermit welds? A) Magnetic Particle Inspection B) Radiography C) USFD (Ultrasonic Flaw Detection) D) Dye Penetrant Test

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   Correct Answer: C Explanation: USFD is the mandatory non-destructive testing method used to detect internal flaws in Thermit welds on Indian Railways.

10. Upset force applied during Flash-Butt welding of 60 kg rail is about A) 200 kN B) 300 kN C) 350 kN D) 450 kN

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    Correct Answer: D Explanation: An upset force of approximately 450 kN is applied to forge the rail ends together during the final stage of Flash-Butt welding.

11. Which of the following gases is NOT used in GMAW of stainless-steel coach body? A) 100 % CO₂ B) Argon + 2% O₂ C) Argon + CO₂ mix D) Pure Argon

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    Correct Answer: A Explanation: 100 % CO₂ is not used for stainless steel as it causes excessive spatter and undesirable carbon pick-up in the weld pool.

12. Auto-Thermit kit introduced by RDSO reduces A) Rail gap B) Fume exposure & start-time C) Welding temperature D) Cost of Al powder

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    Correct Answer: B Explanation: The Auto-Thermit system is designed to improve safety by reducing worker exposure to fumes and decreasing the overall process start-time.

13. The “RailBot-W” project under IR aims to use which advanced welding technology? A) Plasma Arc Welding B) Friction Stir Welding C) Laser-MAG hybrid welding D) Electron Beam Welding

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    Correct Answer: C Explanation: RailBot-W is a research initiative focusing on the automation of rail welding using Laser-Metal Active Gas (MAG) hybrid technology.

14. Which defect is most likely with inadequate pre-heating in Thermit welding? A) Lack of penetration B) Slag inclusion C) Porosity D) Shrinkage cavity

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    Correct Answer: A Explanation: Inadequate pre-heating prevents the rail ends from reaching the fusion temperature, leading to a “lack of penetration” or “cold lap” defect.

15. Permitted hardness in Heat-Affected Zone (HAZ) of rail Thermit weld is A) ≤ 250 HV B) ≤ 350 HV C) ≤ 450 HV D) ≤ 500 HV

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    Correct Answer: B Explanation: To prevent brittleness, the hardness in the Heat-Affected Zone of a Thermit weld is generally restricted to 350 HV or less.

16. Mobile Flash-Butt Welding Plant can complete how many welds per day on running track? A) ~20 welds B) ~40 welds C) ~60 welds D) ~100 welds

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    Correct Answer: C Explanation: High-efficiency mobile plants are capable of performing approximately 60 welds per day depending on traffic blocks.

17. Which organization developed the “Weld-Cloud” app for Indian Railways? A) RDSO B) RITES C) RVNL D) CRIS

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    Correct Answer: D Explanation: The Centre for Railway Information Systems (CRIS) developed the Weld-Cloud application for digital monitoring and data logging of welds.