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Releasing and circulating overshot is one of the fishing tools which can externally engage the pipe, it can fish drill collar, drill pipe, tubing and other pipes. The tools have installed seal, it can circulate drilling fluids in the higher pump pressure after catching the fish. There is a guide shoe at the bottom of overshot which can centralize the fish. It can also work with jars to catch the stuck fish. If the caught fish cannot be release from sticking, it can release the overshot and trip out the drill string.
Structure & Principle
Overshot is composed of three outside parts: the top sub, bowl, and guide shoe. It's inside installed fishing grapple, seal, mill shoe and the mill control. There are two kind of overshot's grapple: spiral grapple and basket grapple, there are different dimension of every kind of grapple. When the fish was led into the bailer, the fish move up to the helical slip, and then rotate left and lift the drilling stem. The helical slip's conical surface and the shell's conical surface cause the relative displacement that makes the slip clinch the fish to achieve fishing. When releasing, land and right rotate the pipe string, and while rotating while lifting until releasing the fish. If the fish diameter is near the maximum catch of the overshot, a spiral grapple, spiral control and type "A" packer is used. If the fish diameter is considerably below maximum catch size (usually1/2"), a basket grapple and a mill control packer are used.
Usage
According to the size of fish choose suitable grapple and seal. Take the overshot connection drilling string (for prevent distortion of the body,so the tongs can't clip both places the internal thread ), the torque connect thread identical the drilling string. Before make a pull, start the pump the mud circulation sufficient. The fish has been held pull out of hole. If it can't unfreezing to hold the fish, pressure overshot 200~500KN and press it several times. After the hook weight increase load pick up drilling string, turn right the drilling tools and pick up slow, it ditto the hook weight till overshot retreat from the fish.
Maintenance
All the overshot has been used must be cleaned and washed, check on the quality of overshot parts, if find flaw, replacing a new one, after install, every threads smear grease and another smear oil to make provision for the future.
Note:
1.there is necessary for inspection before using.
2.Operators need to take care on safety operation and personal safety.
Type | Bowl OD | Max.Catch Size | Connection | |
Spiral Grapple | Basket Grapple | |||
mm (inch) | mm (inch) | mm (inch) | ||
LT-T324 | 324 (12-3/4) | 282.6(11-1/8) | 266.7(10-1/2) | 6-5/8REG |
LT-T298 | 298(11-3/4) | 257.2(10-1/8) | 228.6(9) | 6-5/8REG |
LT-T270 | 270 (10-5/8) | 228.6(9) | 203.2(8) | 6-5/8REG |
LT-T206 | 206(8-1/8) | 177.8 (7) | 159(6-1/4) | NC50 |
LT-T200 | 200(7-7/8) | 171.5(6-3/4) | 155.6 (6-1/8) | NC50 |
LT-T146 | 146 (5-3/4) | 120.7 (4-3/4) | 108 (4-1/4) | NC38 |
LT-T143 | 143(5-5/8) | 120.7(4-3/4) | 108(4-1/4) | NC38 |
LT-T102 | 102(4) | 77.8 (3-1/16) | 65 (2-9/16) | NC26 |