DEVICES FOR MEASURING STRESSES IN A DRILL PIPE

1,267,626. Measuring stresses. INSTITUT FRANCAIS DU PETROLE DES CARBURANTS ET LUBRIFIANTS. April 21, 1970 [April 21, 1969], No.19022/70. Headings G1N and G1W. Axial and torsional stresses in a drilling pipe string are measured by strain gauges 7 and 8 on a relatively thin-walled elastically deformable tubular member 1 incorporated in the drilling string, and a relatively thick-walled tubular safety element 2 is arranged co-axially within (as shown) or around Fig. 3 (not shown) the deformable member 1 so that relative movement between the deformable member 1 and the safety element 2 is possible within predetermined limits, the safety element 2 preventing deformation of the deformable member 1 beyond these limits in the event of excessive stress in the drilling string. As shown in Fig. 1, the safety element 2 is connected to the deformable member 1 by pins 4, 5, 6 fast with the safety element which loosely engage circular or oval holes in the deformable member 1, relative axial and torsional movement being possible within limits set by the pins and holes. Alternatively, Fig.3 (not shown), loosely meshing screw threads (21) may define the limits of relative axial movement, a pin (19) fast with the deformable member co-operating with a hole (20) in the safety element to limit torsional movement. A tubular protection piece 15 or (18) and seals 22, 23 keep drilling fluid from reaching the strain gauges and protect the deformable member 1 from the pressure difference between the inside and outside of the drilling pipe. A plurality of devices may be connected in series with progressively thicker deformable members to cover a wide range of stress. Pressure transducers 16 and 17 sense the fluid pressures outside and inside the drilling pipe. Corrections may be made to the axial stress measurement for the weight of the drilling string below the strain gauges and for the effect of fluid pressure drop in the drilling string if turbodrilling is being done.