Derrick Inspection Red-Flag Conditions

The derrick stands over every pipe trip, every casing run and every BOP test. When it moves, vibrates or settles under load, the whole rig feels it. Most derricks fail slowly: a bent leg, a cracked weld, a loose foundation bolt, a corroded plate. The red-flag conditions are visible if the inspector knows where to look and takes the time to look. A derrick inspection that is rushed or skipped is an inspection that misses the damage until it shows up during the next heavy load. Start at the foundation. The derrick sits on grillage, beams, anchors or a skid base. All of those connections should be tight, level and free of corrosion. A foundation bolt that is loose or missing changes the load path through the leg. A skid base that has shifted on soft ground tilts the derrick and changes the stress on the mast and the dummy board. The inspector should check level and leg load with the mast unloaded and then compare that measurement to the baseline taken after the last rig move. A change in level without a rig move is a change in structure. Leg and brace inspection covers welds, tubing, gussets and connections. Cracks often start at weld toes, at bolt holes, and where bracing meets the leg at an angle. Magnetic particle and dye penetrant testing find the cracks that paint hides. The inspector should look for cracked welds, bent braces, missing lock pins and loose turnbuckles. The derrick should be loaded according to the manufacturer's chart, and the chart should be posted where the driller can see it. Exceeding the rated load because the pipe count looks close enough is how a leg buckles. Traveling block and crown block inspection is equally important. Sheave spacing, sheave rotation, safety latch operation and wire rope spooling all affect the load path. A crown that is out of plumb forces the traveling block to ride on one side of the sheave, wearing the groove and the rope together. A wire rope that nests or crushes in the groove is a rope that will fail early. The inspector should verify that the equalizer bars are working, that the safety latch catches the elevator links, and that the derrickman can see the load from the monkey board. When derrick inspections are tracked with the same rigor as brake tests and pressure checks, the crew keeps a structure that can hold the next load in rig equipment inspection checklist. ← Back to rigs.work