![]() ![]() In the event, powdery dust is an issue at an urban sites, the air hammer typically requires less circulating air volumes from the compressors to drill a large diameter borehole to depth than does the standard reverse circulation rotary (only) drilling rig to drill the same diameter hole to the same depth. This allows the cuttings coming to the surface and exiting the blooey line to be easily captured in open top barrels or commercial waste bins (i.e., no burn pit). Reverse circulation systems are preferred since they can be configured to circulate compressed air in a nearly closed-loop system. These drilling rigs utilize dual wall drill pipe that are rotated with top-drive hydraulic or electric systems. These drill rigs or rigs will typically be equipped to rotary drill with reverse circulation and downhole air hammers and their air hammer bits. Most of these boreholes are typically drilled with larger diameter drill bits, greater than 12 inches (304 mm). These construction projects require the periodic movement of the drilling rig (or the jig containing two rigs) as each borehole or groups of boreholes are completed. These projects usually require multiple boreholes that are placed close together (e.g., often overlapping boreholes). These drilling operations are typically completed to support retaining wall and/or foundation construction projects. Tom Weller, in Air and Gas Drilling Manual (Fourth Edition), 2021 3.4.8 Solids-Gas Separator, “Gas Buster”Īs has been discussed earlier in this manual, there are other shallow drilling applications that are carried out near populated urban areas. Peening is most effective when it is performed under dead load so that the imposed compressive residual stress has to be effective only against the live load. Penetrant inspection of the peened area should be conducted after peening to ensure that embedded flaws are not exposed. Initial passes of the peening hammer may reveal some cracks that were not initially visible, and peening should be continued until the weld toe is smooth and no cracks are apparent. Although peening intensity can be easily varied by changing air pressure, multiple-pass peening at lower air pressures is most effective. Peening should be done using a small pneumatic air hammer with all sharp edges of the peening tool ground smooth. ![]() The expected benefit of peening under favorable conditions (low stress range, low minimum stress) is an increase in fatigue life approximately equivalent to one fatigue design category ( Fisher et al., 1979). Peening can also be applied to uncracked fillet welds to improve the fatigue resistance of the detail. Air hammer peening is effective in arresting fillet weld toe surface cracks with a depth of up to 3 mm if the tensile stress range does not exceed 40 MPa (6 ksi). Peening imposes compressive residual stresses resulting from the plastic deformation induced by the peening hammer and reduces the geometrical stress concentration similar to that with grinding. ![]() Peening is effective as a retrofit for shallow surface cracks that commonly occur at fillet weld toes. Bridge diagnostics, assessment, retrofit, and managementĪlessio Pipinato, in Innovative Bridge Design Handbook (Second Edition), 2022 5.8.3 Peening ![]()
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