Pipe shot blasting: two machines inline

The main variable in a shot blasting process is the operating mix: the distribution of particle sizes in circulation.
For cleaning, the ideal mix has a wide size range: large particles provide the kinetic energy to remove stubborn contaminants, while smaller ones, in greater numbers, achieve full coverage. The recommended setting is to discard particles below 25 % of the nominal size of new shot.
For surface profile, the situation is the opposite. Roughness depends on the kinetic energy of each impact, which is a cubic function of particle size; if the size range is wide, the resulting profile is unstable and uneven. The ideal mix has a narrow range, discarding particles below 50 % of the nominal size.
Both settings are incompatible: with a single machine, a compromise point is set where neither objective is achieved at its best performance.

With two shot blasting machines inline, each is set independently for its designated objective, with no compromise.

Machine 1: shot blasting for cleaning
The first machine runs a wide-range mix with a 25 % discard threshold. It also receives approximately 30 % of the material discarded by machine 2 —which would otherwise be wasted— reusing it as part of the cleaning mix. The fresh shot input is reduced to around 70 %. This machine removes the bulk of surface contaminants, leaving the surface in optimal conditions for the second machine.

Machine 2: shot blasting for surface profile
The second machine runs a narrow-range mix with a 50 % discard threshold. It works on a surface already cleaned by the first machine, which improves the quality of the profile achieved and substantially reduces the risk of contamination between the pipe surface and the coating — the main cause of premature coating failure.

• Most coating failures originate from contamination between the pipe surface and the coating. Machine 2 works on a cleaner surface, significantly lowering that probability.
• With the correct setting of both machines, output can double while keeping a similar cost per m² to a single machine.
• The high-demand pipe coating industry — gas, oil and water pipelines — recognizes the need for two inline machines for this type of process.

Shot blasting does not remove oils or greases. Pipes must enter the machines free of oil residue on their surface. In a two-machine system the risk of contamination failure is lower than with a single machine, but the requirement for oil-free pipe entry remains a process prerequisite.

To define the equipment for your pipe diameter, required output and coating type, our team can advise you.