Boiler parts kitting & sub-assembly

1 Metal Parts Fabrication

CHALLENGES

• Tube Bending Springback: Mandrel-bent inlet tube springs back → angle drifts → won't fit the boiler assembly.
• Stamping Defects: Worn die or 316L thickness variation → wrinkles, cracks, uneven edges on bottom plates and covers.
• Cylinder Body Roundness: Rolling and welding the outer tube can cause ovality or uneven seams, so the bottom plate and cover can't seat properly against it.
• Burrs & Sharp Edges: Laser or stamping leaves a burr on the edge, preventing the parts from closing up tight.

OUR METHOD

• Combined Fabrication: Boiler parts are made by tube bending, sheet metal stamping, and roll forming. We use 316L stainless steel and laser-cut or stamp the bottom plate, cover, baffles, and mounting brackets per drawing.
• Tight Tolerance: To reduce assembly gaps, all stamped parts are produced to ±0.1 mm.
• Precise Bending: A CNC mandrel bending machine forms the inlet tube, ensuring perfect accuracy on bend angles and radii.
• Roll Forming: We roll-form the outer tube with a steady, even weld seam — that keeps it round, not oval.
• Deburring: All cut edges deburred before welding — safe to handle, tight fit-up.

2 Kitting

CHALLENGES

• Missing Components: A single missing baffle, cover, or mounting bracket can halt the entire assembly line.

OUR METHOD

• We kit every component — outer tube, bottom plate, cover, baffles, inlet/outlet tubes, mounting brackets — right off the BOM. Each part gets a label before it hits the bench, so nothing goes missing or ends up in the wrong assembly.
• We use color-coded labels and one bin per complete kit, so the operator grabs the bin and moves on — no picking parts one by one.

3 Incoming Quality Control (IQC)

CHALLENGES

• Tube Diameter Out of Spec: If the inlet tube OD is even slightly off, it won't drop cleanly into the bottom plate hole — that leaves a weld gap and a pressure leak.
• Wrong Material: Using 304 instead of 316L means the part loses its corrosion resistance.

OUR METHOD

• Before assembly, all components are inspected per ISO 9001: dimensions (tube OD, bottom plate fit, hole locations), material certifications (MTC — 316L grade verified), and the quality & quantity of baffles, brackets, and fasteners.
• Any parts that fail inspection are quarantined and returned to the supplier with an NCR (Non-Conformance Report).

4 Sub-Assembly & Automated Laser Welding

CHALLENGES

• Deformation: TIG welding on thin-wall 316L generates significant deformation.
• Weld Quality: This boiler part lives under pressure, vibration, and thermal cycling — a weld with porosity, undercut, or lack of fusion will leak or crack.
• High-precision Inlet Tube: It must seat in the bottom plate hole with a controlled gap — too wide, the weld won't penetrate; too tight, the tube distorts.
• Sub-Assembly Stack-Up: Multiple sub-assemblies (inlet tube + bottom plate, baffles + outer tube, cover) must stack within tolerance, or the final unit won't fit.

OUR METHOD

5 Passivation Treatment

CHALLENGES

• Incomplete Passivation: If the passivation bath isn't properly maintained, the protective chromium oxide layer won't fully form.

OUR METHOD

• We pickle the part to strip heat tint and scale, then immerse it in a citric or nitric acid bath to restore the chromium oxide layer, flipping the boiler and repeating 2–3 times. Bath concentration, temperature, and immersion time are strictly controlled.
• After passivation, parts are rinsed and dried thoroughly to prevent water spots.

6 100% Pressure Testing

CHALLENGES

• Hidden Leaks: Looks fine to the eye, but under pressure a weld seam starts weeping — visual inspection won't catch it.
• Weld Porosity: Tiny pores buried in the weld let pressure bleed through slowly over time.
• Thread or Seal Leaks: Improperly sealed inlet/outlet connections leak during operation.

OUR METHOD

• Every part is pressure-tested at 1 bar after passivation.
• The boiler is sealed at both ends with dedicated test plugs, pressurized to 1 bar with compressed air, then fully submerged in a water tank for at least 1 minute while every joint, seam, and weld line is inspected for bubbles. Even a single bubble means the unit is rejected and reworked — this 100% air-leak test guarantees a leak-proof seal on every part.
• Test results are traceable.

7 Quality Control

CHALLENGES

• Hidden Defects: You can't see inside a weld — internal penetration, baffle placement, weld quality don't show on the surface.
• Dimension Problem: If the center tube hole is out of tolerance or the inlet tube angle is off, it won't fit the boiler assembly.
• Passivation Problem: A part that passes visual may still rust if passivation is incomplete.
• Pressure Leakage: A part that passes visual may still leak under pressure.

OUR METHOD

• FAI: Before running the full batch, the first piece gets a complete dimensional and functional check.
• In-Process Checks: Every 10–20 pieces, we visually check the laser weld, confirm baffle position, verify inlet tube alignment, and run the Go/No-Go gauge.
• 100% Pressure Testing: Every part gets a 1 bar test after passivation; leaking parts are scrapped.
• 100% Visual Inspection: Weld quality, passivation uniformity, and cosmetic appearance checked on every unit.
• Salt Spray Testing: Samples from each batch are tested to verify corrosion resistance.
• Weld Testing: Penetrant testing (PT) or destructive testing on samples to verify weld integrity.

8 Packaging

CHALLENGES

• Transport Damage: Boiler parts are heavy with a passivated finish that is easily scratched or dented; poor packaging means damage during global shipping.

OUR METHOD

• Each boiler part is protected with custom-molded foam inserts or bubble wrap, and we use 5-layer corrugated boxes with added corner protectors to ensure stacking strength.
• Small hardware is individually bagged and secured to prevent loss.

1 Incoming Quality Control (IQC)

• Dimension Inspection: We measure the tube OD, wall thickness, bottom plate dimensions, and baffle thickness with a calibrated vernier, micrometer, and height gauge — tube fit and hole locations get a close look. Hold it to ±0.1 mm.
• Surface Quality Check: Look it over and run a hand across it — sharp edges, burrs, rust, scratches, dents. If your finger catches on anything, it's not passing.
• Material Certification Review: Before we accept a batch, we pull the Mill Test Certificate and check it against the spec — 316L grade verified; chemical composition and mechanical properties have to match. No MTC, no intake.
• Hardware Inspection: We check that the threads and grade markings are legible. If not, we return the lot.

2 In-Process Checks

• Laser Weld Inspection: Check for weld bead uniformity, undercut, porosity, spatter, and crater cracks.
• Baffle Position Check: Confirm baffles are correctly positioned inside the outer tube and securely welded.
• Inlet Tube Alignment: Confirm straightness + angle per drawing. Tolerance: ±1°.
• Center Tube Size: After welding, check center tube size with a Go/No-Go gauge; set aside any failing part for rework.

3 First Article Inspection (FAI)

• Full Dimensional Report: All critical dimensions measured via CMM — overall length, outer tube diameter, inlet tube angle, outlet tube position, mounting bracket locations, and baffle positions. If it's on the drawing, we measure it.
• Assembly Report: Laser weld quality — strong and clean? Baffle position — sitting right? Inlet tube alignment — on angle? Center tube size — pass or fail? No line gets left blank.
• Material Verification: We check the MTC to confirm the 316L grade. If the grade doesn't read right, the batch doesn't come in.
• Surface Finish Check: Look over the whole surface — is the passivation even? Any heat tint left behind? Any contamination or discoloration? If the color isn't uniform, something went wrong in the bath.

4 Random Sampling (AQL-Based)

• We pull a random sample based on ISO 2859-1, running at AQL 1.0 for the overall standard.
• Sample Size: Depends on the lot — a batch of 500 pieces → we pull 50 to inspect. The bigger the lot, the bigger the sample, per the table.
• Inspection Items: Dimensions, laser weld appearance, baffle position, passivation quality, and mounting hole position.
• If the sample defects stay under the AQL limit, the whole lot passes.

5 100% Inspection

• Every part gets checked — no sampling, no shortcuts.
• Pressure Test: After passivation, each part goes on the rig at 1 bar. If it leaks, we pull it and scrap it on the spot.
• Laser Weld & Assembly Check: We visually inspect every part — weld defects, baffle position, and inlet tube alignment. Nothing leaves without this check.
• Passivation Check: We check heat tint, scratches, or contamination visually. If the surface isn't clean and uniform, it doesn't pass.
• Center Tube Hole Size: Insert Go/No-Go gauge pins into the holes to confirm the diameter.

6 Functional & Environmental Testing

• Pressure Test: 100% 1 bar pressure test to verify weld integrity; leaking parts are scrapped.
• Weld Testing: Penetrant testing (PT) or destructive testing on samples to verify weld penetration and strength.
• Salt Spray Test: From each batch we pull sample pieces and put them in the salt spray chamber. The standard is at least 240 hours with no corrosion.

7 Fitment Check (Go/No-Go Gauge)

• Inlet Tube Angle Check: Verify the inlet tube angle against the drawing using a protractor or profile gauge. Tolerance: ±1°.
• Center Tube Hole Size: Insert Go/No-Go gauge pins into the holes to confirm the diameter.