Welding Methods
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)
| Element | IS:90 (52 kg), IRS-T-12 (60 kg) |
|---|---|
| C | 0.65–0.80 % |
| Mn | 0.90–1.30 % |
| Si | 0.15–0.30 % |
| P & S | ≤ 0.035 % |
| UTS | 880–980 MPa |
| Hardness | 260–300 BHN |
High carbon & alloy → hardenability & crack sensitivity → governs welding procedure.
3. Classification of Welding Processes used on IR
A. Fusion Welding (melts base metal)
- Gas Pressure Welding (GPW) – Thermit® process (Alumino-thermic)
- 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)
- Flash-Butt Welding (FBW) – mobile & fixed plants
- Electro-slag / Electro-gas – thick web crossings
- Laser, Plasma, EBW – Metro & LHB coach body (stainless steel)
B. Solid-State Welding (no melt)
- Friction Welding – Alstom LHB wheel-axle
- 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
| Defect | Cause | NDT | Accept limit |
|---|---|---|---|
| Lack of penetration | Low pre-heat | USFD | Zero |
| Slag inclusion | Fast travel | Radiography | ≤ 3 mm any dir. |
| Porosity | Moist electrode | UT/X-ray | ≤ 2 % area |
| Undercut | High current | MPI | ≤ 0.5 mm deep |
| Cold shut (Thermit) | Mis-alignment | UT | Not permitted |
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?
Answer: b) Fe₃O₄ + Al
2. The pre-heating temperature required before pouring Thermit metal is about
Answer: c) 900–1,000 °C
3. Standard gap kept between rail ends during Thermit welding is
Answer: a) 25 mm ± 1 mm
4. Which welding process gives the smallest HAZ width on rails?
Answer: d) Flash-Butt Welding
5. The first rail weld in Indian Railways was carried out in the year
Answer: b) 1928
6. Current required for Flash-Butt welding of 60 kg UIC rail is approximately
Answer: c) 55–65 kA
7. Which electrode is recommended for welding IRSM-44 freight wagon underframe?
Answer: a) AWS E7018
8. The minimum transverse tensile strength accepted for a Thermit weld joint is
Answer: b) 720 MPa
9. Which NDT technique is mandatory for 100 % inspection of field Thermit welds?
Answer: c) USFD
10. Upset force applied during Flash-Butt welding of 60 kg rail is about
Answer: d) 450 kN
11. Which of the following gases is NOT used in GMAW of stainless-steel coach body?
Answer: a) 100 % CO₂ (causes excessive spatter & carbon pick-up)
12. Auto-Thermit kit introduced by RDSO reduces
Answer: b) fume exposure & start-time
13. The “RailBot-W” project under IR aims to use which advanced welding technology?
Answer: c) Laser-MAG hybrid welding
14. Which defect is most likely with inadequate pre-heating in Thermit welding?
Answer: a) Lack of penetration
15. Permitted hardness in Heat-Affected Zone of rail Thermit weld is
Answer: b) ≤ 350 HV
16. Mobile Flash-Butt Welding Plant can complete how many welds per day on running track?
Answer: c) ~60 welds
17. Which organization developed the “Weld-Cloud” app for Indian Railways?
Answer: d) CRIS
BETA
