How to deal with air leakage after installation of stainless steel welded air duct?

Treatment scheme of unqualified air leakage test after installation of stainless steel welded air duct

> application: stainless steel welded ventilation pipes, weld air leakage, flange air leakage, soft joint air leakage and pipe joint air leakage are generally tested by light leakage method/air leakage quantity.

First, locate the leak (screening sequence)

1. Weld position: the most common leakage points in stainless steel welding, such as continuous weld porosity, slag inclusion, incomplete penetration and spot welding splicing gaps; Especially the girth joints of corners, reducers, elbows and flanges.

2. Flange connection parts: flange surface deformation, gasket damage, gasket dislocation, uneven bolt tightening torque and flange warping.

3. Soft joint (canvas/silicone soft joint): the pressure joint between the soft joint and the air duct flange is not in place, and the soft joint itself is damaged.

4. Air duct opening: pressure tap, maintenance port, branch pipe interface and regulating valve joint.

5. Perforation position of reinforcement and hanging yard: the pipe wall is perforated and bolted without sealing treatment.

Simple leak finding method

Light leakage method: strong light is played in the air duct, and the transparent position is the leakage point when viewed from the outside;

Wind pressure and pressure maintenance test: the system maintains working pressure, and soapy water is brushed outside, and the bubbling place is the leakage point.

Second, the treatment methods of different leakage points

1, weld air leakage (stainless steel body welding seam)

1. Small pores and tiny gaps: polish the leaking area, remove scale and oil stain, and repair welding again; Priority is given to argon arc welding of stainless steel, and serious intergranular corrosion caused by ordinary electric welding is prohibited.

2. Large-area incomplete penetration and cracks: it is necessary to polish and remove the original weld, re-weld, and clean the welding slag and oxide layer after welding.

> note: after repair welding of stainless steel, it is necessary to passivate the weld by pickling to prevent later corrosion; Don't directly use glass glue to cover up the air leakage of the weld. When the wind pressure is high, the glue will fall off, which is a temporary remedy and cannot replace welding.

> there is only a low-pressure breeze ventilation system, and when hot work cannot be carried out at the site, high-temperature resistant silicone sealants/butyl sealing tape can be temporarily used for temporary plugging, and repair welding is still recommended at the later stage.

2. Air leakage at flange position

1. Flange warping deformation: correct the flange plane, and replace the flange if the deformation is serious;

2. Sealing gasket: replace a complete and undamaged heat-resistant rubber/silica gel gasket, which should be complete, without fracture or splicing gap; Center the gasket, and don't extend into the air duct;

3. Bolts: Tighten diagonally evenly, and don't screw them to death at one time; Missing bolts are filled.

3, soft connection air leakage

Flange blank holder shall be pressed tightly, and soft joint shall not be twisted and pulled; Replace the soft joint directly if it is damaged, and apply additional sealant at the joint.

4, pipe wall opening, manhole, valve interface air leakage.

Aging and replacement of sealing strip of manhole cover plate; Add sealing gasket to valve flange; The inner and outer surfaces of all perforated bolts on the pipe wall shall be sealed with weather-resistant sealant.

Third, retest after the repair is completed

1. After all the repairs are completed, clean up the welding slag and rubber debris inside the air duct;

2. Re-test the light leakage or air leakage, and the air leakage meets the limit value according to the construction quality acceptance specification of ventilation and air conditioning engineering and the system pressure grade (low-pressure/medium-pressure/high-pressure air duct);

3. The high-pressure air duct shall focus on reviewing all welds, and it is strictly forbidden to replace welding with sealant only.

Four, the main points of preventing subsequent air leakage again

1. Full welding is preferred for stainless steel air duct welding to reduce spot welding; Clean up the oil stain on the plate before welding;

2. Flange processing ensures flatness, and the installation gasket is intact;

3. When hoisting the air duct, minimize the opening of the pipe wall, and the opening position must be sealed both inside and outside;

4. After welding, do pickling passivation in time to avoid new leakage holes caused by weld corrosion.