How to solve the air leakage problem of stainless steel welded ventilation pipeline?

Complete solution to air leakage of stainless steel welded air duct (including field repair, flange sealing, radical treatment of vibration cracking and preventive technology)

I. Air leakage of weld body (sand holes, air holes, incomplete penetration, cracks, spot welding gaps)

1. Tiny pinholes and blowholes (slight leakage)

Angle grinder grinds 20mm around the leakage point to remove scale, blackened welding slag and oil stain;

The inside of the small tube is filled with argon for protection, and the 0.6–1.5 mm stainless steel sheet is repaired by DC argon arc welding;

Single-point small holes are directly spot-welded and filled, and continuous air holes are gouged along the weld to be fully welded again;

After cooling, it will be polished flat, and there will be no bright spots in the light transmission re-inspection.

2. Incomplete penetration, one-sided welding of the back through the gap (large air leakage)

Open a V-groove along the outside of the weld to clean up the internal oxide layer;

Argon gas is introduced into the tube to isolate the air, so as to prevent the back surface from being oxidized again.

Full welding and filling in sections to avoid thermal deformation caused by long-time welding at one time;

The condition of thick-walled air duct allows double-sided welding to fuse and plug the gap from the inside and outside.

3. Weld crack (cold and hot stress, vibration tearing)

Both ends of the crack are extended by 5mm to grind the groove to prevent the crack from continuing to extend;

Choose matching stainless steel welding wire (ER308 for 304 and er316L for 316l);

Slow welding at low temperature and intermittent welding in sections to reduce thermal stress;

Long-term high-temperature exhaust pipe can be tapped to relieve stress after welding and equipped with expansion compensator.

4. Jerry-built spot welding and intermittent long gaps

All the original spot welds shall be polished, and the whole through seam shall be fully welded. It is forbidden to fix them by spot welding only at intervals.

Second, the flange joint air leakage (one of the highest leakage points)

Flange deformation, warping and loose fitting

Slight deformation: jack and fixture are used to correct the flange plane;

Severe deformation: cut off the old flange, re-blank and fully weld the new flange, and correct the flatness after welding.

Failure treatment of gasket

Remove aging, broken and spliced gaskets, and replace the whole ring of non-spliced heat-resistant rubber/silica gel gasket;

The thickness of gasket shall be uniform 3-5mm, and multi-layer superposition and partial lack of gasket are prohibited;

Flange contact surface shall be cleaned of welding slag and burr, and Bo Tu high-temperature sealant shall be used for gasket.

Bolt fastening is not standardized.

Strictly tighten diagonally and step by step (2-3 times) to avoid flange warping caused by unilateral compression; Complement the missing bolts, and replace the corroded bolts with stainless steel bolts.

Three, special-shaped pipe fittings, soft joint, valve interface air leakage

Elbows, tees and variable diameter welds are leaking: all the welds are inspected for light transmission, and sand holes are repaired one by one, and small current fine argon welding is carried out at the dead angle;

Canvas soft joint/stainless steel compensator leaks at both ends: replace the damaged soft joint and completely compact the flange gaskets at both ends; Soft flanging weld perforation needs repair welding;

Fire damper, muffler and manhole: replace the aging sealing strip, tighten the cover screws evenly, and re-glue and gasket the valve body flange.

Four, lifting, vibration, stress tear air leakage (air leakage after use for a period of time)

Insufficient supports and hangers and excessive hanging distance: add hangers and anti-sway brackets to reduce vibration transmission of fans;

Support directly burns through the pipe wall: the original hole is polished and repaired, and the new support is fixed by hoop. It is forbidden to directly weld the air duct cylinder;

Hot-cold expansion crack weld: stainless steel expansion joint is installed in high-temperature air duct to release the stress of thermal expansion and cold contraction;

Flexible soft joints are added to the short pipes at the inlet and outlet of the fan to block the welding seam of the vibration transmission duct.

Five, the parent metal damage, bending crack air leakage

Small holes bumped during transportation and hoisting: repair welding by argon arc welding after grinding;

Invisible micro-cracks in the corner: the groove in the crack area is polished, and the whole hem is fully welded and reinforced;

Large-scale scratch and thin-wall deformation: local replacement of plate splicing, full welding and sealing.

Six, emergency temporary plugging (unable to hot repair welding site)

Suitable for computer rooms, explosion-proof areas, and suspended ceilings that cannot be used for hot work:

Micro-trachoma: stainless steel special high-temperature sealant+stainless steel aluminum foil tape double-layer package;

Slim gap: polished clean, coated with metal mending agent, wrapped with temperature-resistant aluminum foil tape for compaction;

Note: the temporary rubber plug is only used temporarily, and the long-term running air duct must be permanently blocked by argon arc welding.

Seven, after the completion of leak detection verification (to prevent rework)

Light leakage detection (simplest)

One end of the air duct is illuminated by strong light, and whether there are light-transmitting bright spots is observed externally, and all bright spots are marked for repair welding;

Wind pressure and air leakage test

Block the air duct in sections, supply air and pressurize it, spray the weld and flange with soapy water, and the foaming position is the leakage point;

After the completion of the repair, the second re-inspection will be qualified if there is no light leakage and no bubbles.

Eight, prophase preventive measures (reduce air leakage from the source)

Stainless steel welding must be protected by argon filling in the pipe to prevent honeycomb pores in the weld;

All butt joints, flanges and special-shaped parts are fully welded, and spot welding is strictly prohibited to replace them;

Flange blanking is smooth, and the fixture is fixed during welding to reduce deformation;

Reasonable arrangement of supports and hangers and expansion compensators to reduce vibration and thermal stress;

After the production is completed, leak detection should be carried out first, and then hoisting and installation should be carried out to avoid rework after the ceiling is suspended.