Graco’s EcoQuip vapour abrasive blast equipment was thoroughly tested for use in potentially hazardous areas involving explosive atmospheres
Abrasive blasting often has to take place in hazardous or explosive environments, such as the power generation, construction, oil and gas, shipping, petrochemicals and chemicals industries, and where flammable liquids, vapours or combustible dusts exist.
In such environments, it’s vital to use abrasive blasting equipment that has been fully tested to determine whether the blasting process might lead to an ignition. EcoQuip is Graco’s vapour abrasive blasting equipment. It’s been proven to be suitable in different industries for a range of applications such as the removal of paint, rust, corrosion, industrial coatings and linings; for cleaning metal, stone and woodwork; and for building and site maintenance. In all these applications, EcoQuip has been demonstrated to reduce project costs and increase the speed, efficiency and productivity of blasting.
PUTTING ECOQUIP TO THE TEST
Gexcon AS of Bergen, Norway, a world- leading company in the field of safety and risk management, and advanced dispersion, explosion and fire modelling, was asked to perform tests to determine whether sparks generated by the EcoQuip system would be potential sources of ignition. The experiments were performed at Gexcon’s test site at Børnesskogen, Norway in May 2019.
EcoQuip is intended (and is ATEX approved) for use in atmospheres of flammable materials in the Equipment Protection Level (EPL) Subgroup IIA. This subgroup of explosive gases includes diesel fuels, petrol fuels, hexane, methanol, propane, ethane, acetone, toluene, benzene and methane. For the purposes of this test, hexane was selected. At a concentration of only around 4% in air, hexane is not only extremely sensitive to electrical sparks, but is easy to ignite. It has an auto ignition temperature of 230 °C. Tests were therefore performed in explosive atmospheres with a rich concentration of n-hexane. The tests were performed in a 50 cubic meter testing vessel. It had to be relatively large due to the air coming into the system from the blasting equipment diluting the gas mixture. Its large size would also permit a longer duration of the tests. The vessel was open at one end, which was covered with a plastic sheet to contain the combustible gas/air inside the vessel as well as to relieve the pressure of an explosion should one occur. The vessel was equipped with a recirculation system with a n-hexane evaporation system.
Pure n-hexane vapour was injected into the recirculation system to gradually increase the n-hexane concentration inside the vessel. N-hexane concentrations around 7% were normally used as the starting concentration and diluted to around 4% for all tests. The mixture of n-hexane vapour and air inside the vessel was monitored with a binary gas analyser from Stanford Research Systems Inc. EcoQuip was positioned on the outside of the test vessel, while the nozzle was inside the test vessel. A Graco standard #7 blast nozzle (7/16”, 11mm) was used during the tests. The nozzle was connected via a 15 metre hose to the equipment. EcoQuip was earthed to the test vessel using its green earthing cable. The nozzle was mounted in rubber mounting brackets to prevent it from being earthed to the steel in the vessel in order to best simulate a person holding the nozzle. EcoQuip was supplied with water from a 1000 litre water tank standing on the roof of the testing vessel, about 3 metres off the ground. Only gravity from this tank was used to supply the system with water. A Kaeser M122 air compressor provided a steady pressure of typically 7.5 bar (110 psi). Five different abrasives were used with the Graco EcoQuip vapour abrasive blasting equipment during the test: •
- 30/60 mesh Garnet (GMA). • 80 mesh Garnet (GMA). •
- Fine Copper Slag 0.2-1.0 mm grit size (Star Grit). •
- Coarse Copper Slag 0.4-1.9 mm grit size (Star Grit). •
- Fine Crushed Glass 0.2-0.6 mm.
Blasting was performed on rusty steel and aluminium plates of approximately one square metre. These could be moved during a test, making it possible to blast on new material. The five abrasives were used on both steel and aluminium plates, making a total of ten test runs. The duration of each test run lasted between 3.2 and 7.5 minutes. The abrasives and blasting materials were chosen to cover the typical worst-case combinations when it comes to spark generation.
ECOQUIP PASSES WITH FLYING
None of the tests yielded an ignition. After the last test, the explosive atmosphere inside the vessel was ignited using an oscillating spark in order to confirm that the atmosphere was indeed explosive. (It was!). Gexcon therefore fully endorses Graco’s EcoQuip vapour abrasive blasting equipment as suitable for use in potentially hazardous areas involving explosive atmospheres caused by gases and vapours of the Subgroup IIA. These tests support EcoQuip’s ATEX ignition hazard analysis for category 2 equipment in zone 1 explosive atmospheres. ■