Leaking, drill pipe

Drillpipe washouts are cracks in the drill pipes, causing a mud leak. The detection of drillpipe washouts is done by recording in normal drilling ... 

A leak develops in the pipe string. The standpipe pressure reading drops to 1,896 psi with the same mud flowrate and the downhole drill collar inside pressure drops to 6,700 psi. What is the flowrate of the leak What is the area of the leaking hole assuming it is located at 3,000 or 5,000 or 7,000 ft (Assume that AP annulus does not change.)... 

Sentinel holes are used as a simple form of thickness testing. A small hole of about I - 6 mm diameter is drilled from the outer wall of the piece of equipment to within a distance from the inner wall (in contact with the corrodent) equal to the corrosion allowance on the equipment (Fig. 9.11). The technique has been used even in cases where the corrodent spontaneously ignites on contact with the atmosphere. The philosophy is that it is better to have a little fire than a big one which would follow a major leak from corrosion through the wall. When the sentinel hole begins to weep fluid a tapered plug is hammered into the hole and remedial maintenance planned. Siting the sentinel holes is somewhat speculative although erosion at the outside of a pipe bend is often monitored in this way. 

On older process units, you may still encounter piping with sentry holes. Let s say I have a Vfc-in thick pipe. The corrosion allowance for the pipe is Vi in. A number of small holes are drilled into the pipe, to a depth of in. When we start leaking at these small holes, this means that the pipe has corroded to its discard thickness in the area of the sentry hole. Incidentally, you can stop the resulting leak, at least in carbon steel water lines, with a brass wood screw and a screwdriver. I have also done this on hydrocarbon lines under an 80 psig pressure, but perhaps that is not too smart. 

A test simulating a leak in a loop was made to study this phenomenon. A 2 % Cr-1% Mo steel pipe was filled with Bi containing 1000 ppm U, 350 ppm Mg, and 250 ppm Zr. A 1 /32-in. hole was drilled in the pipe below the Bi level. A patch of asbestos tape 2 in. in diameter was put over the hole. The tube was then heated to 594°C and pressurized to 5 psi to force out a small amount of Bi. The pressure was dropped as soon as some Bi had leaked out and the tube was then heated at 594°C for 1025 hr. The appearance of the pipe underneath the asbestos tape patch and a cross section of the oxidized area are shown in Fig. 21-11. A complete oxidation through the pipe wall has occurred in the area adjacent to the leak. 

N.B. Bolts were tightened to a torque of 135 Nm during installation, and pressurization was done at a rate of approximately 1 MPa/min. The pipe is drilled (and tapped) with a single quarter in BSP through hole to simulate leaking. 

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