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Program Planning & Execution — Larsen & Toubro
Problem 1: Finding the Optimal Turning Points for Long-Seam Welding
SITUATION : At L&T Heavy Engineering, Tube sheets are mission-critical circular steel plates used in heat exchangers and reactors to join and support hundreds of tubes. First, the tubesheet is welded (plate sections are joined by long seam welding to form a circular assembly), then later the holes are precisely drilled. The challenge is : During long seam welding, the thermal expansion and contraction cycles create unavoidable angular distortion and warping. The final flatness and dimensional accuracy of the tubesheet directly determine whether the 1000+ precision-drilled holes will be within tolerance when drilling occurs or the tube sheet will be scrapped.
Manufacturing had traditionally relied on a reactive, hunt-and-correct approach: weld continuously, measure distortion, apply straightening repeatedly until flatness was achieved.
This reactive approach created few critical risks:
- Risk 1: Over-Machining & Scrap: If the tube sheet "cups" or "wings up" excessively, correcting it through rework removes material unevenly, potentially reducing wall thickness below structural requirements. Result: tube sheet rejection or scrap.
- Risk 2: Uncontrolled Production Delays & Cost:
- Reactive corrective turns (8-10 turns "until flat" before drilling): 4-8 hours extra crane/rigging time per turn.
- Thermal straightening and mechanical pressing: adds days to schedule.
- Risk of catastrophic scrap: $50,000-$200,000+ per failed tubesheet + weeks of lost production.
Need : A predictive turning schedule, flipping the plate at scientifically-determined weld deposition percentages prevent distortion accumulation during welding itself.
ACTION
- Real-Time Monitoring: Monitored in detail the fabrication of four tube sheet (8T, 8B, 9T, 9B) with varying thicknesses (30mm, 40mm) using Submerged Arc Welding (SAW) at controlled parameters (400-450A, 28-32V, 350-400 mm/min travel speed) and Applied rechambering (pre-angling sheets opposite to expected distortion direction) combined with mid-process plate flipping to leverage gravity and thermal forces.
- Measurement : Measured angular distortion at each welding pass using laser measurement against calibrated reference planes, capturing both magnitude and direction. Tracked weld deposition thickness at each turn point and corresponding deflection magnitude (mm).
- Analysis: Plotted deflection vs. weld deposition thickness for all four samples, identifying consistent patterns across different thicknesses.
KEY FINDINGS (Table I Analysis):
- Turn 1 Optimal Point: First plate flip should occur at 30-35% of total weld deposition thickness.
- Turn 2 Optimal Point: Second flip at 64-80% weld deposition (average 72%) Consistent timing across all four samples regardless of base plate thickness.
- Distortion Pattern: Maximum deflection occurred just before each turn, then decreased after flipping due to gravity assistance.
RESULT
- Optimized Turning Schedule: Established science-based turning points (Turn 1 @ 30-35%, Turn 2 @ ~72%) eliminating rework of (~5000$ per sheet) and minimizing final distortion, thus saving 40 hrs of time for 01 tube sheet manufacturing.
Problem 2: Determine turns for flatness control in Electroslag Overlay Welding
SITUATION : After long seam welding, tubesheets require weld overlay (cladding) on inner surfaces to enhance corrosion resistance and mechanical properties for harsh operating environments. Electroslag Strip Welding (ESSW) overlay process induced secondary distortion patterns that compromised flatness tolerance. Critical flatness specifications had to be maintained throughout the overlay process to prevent downstream manufacturing issues (tube-to-tube sheet joint alignment). Manufacturing needed to identify a solid threshold for the welding thickness and turns.
ACTION
- Experimental Setup: Conducted overlay welding on four pre-welded tubesheet samples using ESSW (Electroslag Strip Welding) at controlled parameters: 500-600A, 23-25V, 160-170 mm/min travel speed, record EST 122 flux.
- Coverage-Based Monitoring: Tracked flatness as cumulative area coverage progressed from 0% to 100% (50% per side = 100% total coverage) and Recorded flatness variation (in mm) using laser measurement, against cumulative coverage percentage (0%, 30%, 45%, 60%, 75%, 95%, 100%).
- Analysis: Plotted cumulative coverage % vs. flatness distortion, identifying critical control zones and distortion thresholds.
KEY FINDINGS (Flatness Analysis):
- Phase 1 (0-45% coverage): Flatness varied between -45mm to +25mm (wide tolerance zone).
- Phase 2 (45-75% coverage): Distortion pattern stabilized with max variation of ±40mm.
- Phase 3 (75-100% coverage): Distortion converged toward final flatness of +9mm (controlled zone).
- Optimal Zones Identified: Clear patterns showing when to apply tighter control vs. when relaxed tolerance acceptable.
RESULT
- Process Optimization & Flatness Strategy: Provided manufacturing teams with specific flatness checkpoints, preventing costly, excessive rework during final stages.
- Production Framework: Enabled real-time process adjustment, if flatness exceeds limits at specific coverage %, corrective welding sequence or parameter adjustment can be applied immediately.
- While covering 0% to 45% of cumulative area of the plate by overlay welding- keep flatness limit as 40mm. (relaxed tolerance during initial overlay).
(If you reach the 45% area coverage mark and your plate has warped more than 40mm, you must stop and take corrective action such as adjusting the welding sequence, using stronger restraints, or applying counter-heat before continuing. If you continue, the final part may be so distorted that it cannot be machined down to the final required dimensions.)
- For area 45% to 75% keep flatness limit as 25mm (moderate control during mid-phase).
- For the last 25% i.e while covering area from 75% to 100% keep flatness strict.
Summary of what we saved:
- Scrap Risk which can cost $50,000-$200,000 per failed tube sheet, weeks of production loss.
- Costly rework of around 5000$ per sheet and material loss.
- Reducing material below safety minimums, extra crane operations: 4-8 hours per tube sheet in unnecessary handling.
- Rework Labor: Dozens of man-hours in corrective machining and pressing per reactor.
Problem 3: Roller Design for the movement of Hydraulic Jack
SITUATION : During pressure vessel fabrication at L&T Heavy Engineering, large assemblies (150T+) required precise positioning and movement within the workshop. Standard overhead cranes could lift the pressure vessel, but positioning the hydraulic jack below it presented a critical constraint. Because the pressure vessel was lifted by the overhead crane, it blocked access to the hydraulic jack by another crane. A custom roller solution was needed that could support the full weight of the hydraulic jack to enable smooth lateral displacement to position correctly for the pressure vessel to be placed on it, problem requiring structural design under load.
ACTION
- Problem Analysis: Identified the constraint : overhead crane unable to access the hydraulic jack due to the vessel that is held in air by another over-head crane.
- Design Approach: Applied shaft design theory (bending moment and shear stress analysis) to determine roller diameter capable of sustaining 8-ton point loads, Uniform distributed load, across a 700mm span.
- Calculation & Validation: Computed bending moments at critical points (A, B, C, D) along the roller span. Applied maximum bending stress theory (0.66Fy) to determine required diameter: 50mm solid shaft. Cross-verified using shear stress theory (Sys = 0.577Syt) yielding 41.6mm diameter. Selected 50mm diameter to ensure structural safety margin under load.
- Design Output: Provided detailed dimensional specifications (700mm span, 50mm diameter) for manufacturing and attachment to the hydraulic jack.
RESULT
- Engineered Solution: Delivered roller design capable of supporting the uniform distributed load of 8T of the hydraulic jack while enabling its longitudinal movement within confined workspace. Thus Enabled safe movement of the hydraulic jacks in congested work areas, improving efficiency and worker safety in the workshop.
OVERALL INTERNSHIP IMPACT
Delivered a transformational manufacturing framework for pressure vessel tube sheet production at L&T Heavy Engineering, shifting from reactive, costly post-weld correction to predictive, in-process distortion control. Demonstrated ability to solve real-world production constraints through applied physics and systematic problem-solving.
