RAILWAY BRIDGE SAND BLASTING

Working on a victorian railway bridge, as part of a restoration project. This bridge was in a poor state and needed to be restored in order to preserve its history.

SAND BLASTING OR ABRASIVE BLASTING

This structure needed to be preserved. So I was contacted and asked to undertake the first stage of the project, Abrasive Blasting or Sand Blasting the main structural areas of the bridge. These areas had to be fully blasted prior to inspection & any repair work being carried out. 

HIGH PRESSURE ABRASIVE BLASTING

The main areas of this steelwork where very corroded, with heavy deep rust pitting and scale, making this structure a (Grade “D” Substrate) The class of blast required was SA 2.5

(A thorough clean with less than 5% shading) SA 2.5 is a high class of blast for such a poor substrate. 

OBJECTIVE 

The project plan, was to remove all the rust pitting & scale from the surface of the main structural parts of the structure. So that a full inspection could be carried out. Then all the necessary repairs could be undertaken. These areas were blasted with a nozzle pressure over  a 100 psi @ the nozzle. The blast media of choice for this job was iron silicate. The structure used five tons of blast media, just to remove the heavy rust pitting and scale from the lower and underside main beams and braces. By looking at the photos in the photo gallery, you will see there was a lot of rust and scale to remove from this substrate, to gain a SA 2.5 class of blast. Some parts of the bridge, had rust scale up to 1/2 inch thick in some places on the underside.

At the start of each day the temperature was tested (humidity levels) & the nozzle pressure was measured using a hypodermic blast pressure gauge, to test the true blasting pressure at the nozzle. Anything less than 100 psi at the nozzle is inefficient in many ways, both in velocity (the speed of the air exiting the nozzle)  With anything less than 100psi at the nozzle, the consumption of fuel and blast media increases, because the blast media impacts the surface of the steel with less velocity and force, requiring you to spend longer blasting the same given area. This all boils down to the simple fact of efficiency.

TOOLING

The set up  was a 400 CFM  compressor running at over 100psi @ the nozzle. The air was after-cooled first & then passed through a coalescent filter/water separator. The blast pot used was pressure hold system, running a 1 1/4 inch blast house, up to 30 m in length. These types of system have to be very well planed, in order to get these pressures at the nozzle, when using  long hose lengths.

Big Bull hoses are required along with as few restrictions in the whole system as possible. This is essential to reduce pressure losses in the system.

At CJK ABRASIVE BLAST CLEANING AND SURFACE PREPARATION we spend a great deal of  time & focus on system efficiencies. When you start running long hose lengths, you do require some substantial supply houses, with large internal dimensions, to counter act any pressure drops in the blasting system.

HISTORY

This Victorian bridge structure passed over the old North to South Railway line in the area. The bridge was a 3 arch brick construction, with a roadway passing over the main railway span. The sides were constructed from steel sheets, angles and braces hot riveted together by hand, to form the structural sides of the bridge. Some of the steelwork in the sides is below ground level. This had to be excavated in order to gain access to these main structural parts, these areas would be recovered again, once inspected and the necessary repairs had been carried out.

This was a great project for us at CJK as we have built up powerful systems and equipment, along with knowledge to undertake such structures.

CJK we’re quality comes first.