US3226977A

US3226977A - Safe operating condition indicator

Info

Publication number: US3226977A
Application number: US297805A
Authority: US
Inventors: Robert H Kolb
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1963-07-26
Filing date: 1963-07-26
Publication date: 1966-01-04
Anticipated expiration: 1983-01-04

Description

Jan. 4, 1966 R. H. KOLB SAFE OPERATING CONDITION INDICATOR 2 Sheets-Sheet 1 Filed July 26. 1963 R O T N E V N n m N O R K m H U T WW H w? R R. H. KOLB SAFE OPERATING CONDITION INDICATOR Filed July 26. 1963 2 Sheets-Sheet 2 DEFLECTIDN TRANSDUCER 301 ii ANCULAR DEFLECTION l j: lksg l HOOK LDAD TRANSDUCER STRESS CONVERTER X'Y PLDTTER INVENTOR:

ROBERT H. KOLB BYI WW HIS ATTORNEY United States Patent 3,226,977 SAFE OPERATING CONDITION INDICATOR Robert H. Kolb, Houston, Tex, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 26, 1963, Ser. No. 297,805 8 Claims. (CI. 73-89) This invention pertains to an apparatus for producing an indication when the operating conditions cause the total stress on a string of pipe used in the drilling or completing of an oil well to approach the maximum permissible stress. More particularly, this invention pertains to an apparatus for measuring the deflection of a string of pipe relative to an axis perpendicular to the deck of a drilling platform and producing an indication whenever the stress in the string of pipe due to the deflection and to the axial load, commonly referred to as the hook load, approaches the maximum permissible stress for the particular pipe being used.

In the drilling and completing of oil wells, any string of pipe which is lowered into the well from the well derrick is subject to an axial stress caused primarily by the weight of the string and a bending stress caused by the deflection of the pipe from the vertical. In most wells drilled on land, due to the stable drilling platforms and consequently the relatively small lateral movement of the pipe string, the deflection of the pipe string can be neglected. However, in offshore or underwater wells drilled from floating platforms where the platform is continually moving, both laterally and due to pitch and roll, relative to the well located on the floor of the body of water, the stress due to deflection cannot be neglected since it contributes greatly to the total stress in the pipe string.

One method of determining the stress on a string of pipe has been to measure the hook load and then determine the deflection of the drilling platform from the axis of the well. From these determinations the total stress on the string of pipe may be easily calculated. Where the deflection of the string of pipe or well tubular goods is apt to change from moment to moment, as for example when the string of pipe is suspended from a floating platform, the previously used method is not adequate since it has numerous disadvantages. Some of these disadvantages are that the previously described method requires the continuous attention of one of the operating personnel and that the determinations of the total stress tend to lag behind the applications of the stresses and thus fail as a warning of the approach of a dangerous condition.

In order to overcome the previously mentioned disadvantages, systems have been developed for automatically producing an indication proportional to the total stress on the well tubular goods. Such a system is shown in the copending application of Keith Doig and Kenneth W. Foster, Serial No. 275,180, filed April 16, 1963. The apparatus as disclosed in this copending application generates a pair of voltages, one of which is proportional to the stress due to the hook load and the other of which is proportional to the stress due to the deflection, and then algebraically combines these voltages to ascertain that the sum voltage, which is proportional to the total stress on the well tubular goods, does not exceed a voltage which corresponds to the maximum permissible stress for the particular well tubular goods being used. Although such a system operates satisfactorily, the apparatus necessary for the calculations requires complicated switching circuitry in order to allow the apparatus to perform the comparisons for the many difierent design characteristics of well tubular goods used. Furthermore, the prior means disclosed for generating a voltage proportional to the total deflection of the string of pipe included 3,226,977 Patented Jan. 4, 1966 a relatively complicated system requiring the generation of a plurality of voltages proportional to the deflection of the string of pipe in two planes at right angles to each other which voltages must then be vectorially added together.

Accordingly, it is a principal object of this invention to provide a simplified means for automatically comparing a quantity proportional to the total stress on a string of pipe subject to both an axial stress and a stress due to deflection of the pipe string to the maximum permissible stress for the particular drill pipe being used.

A still further object of this invention is to provide a system for producing an indication whenever the operating conditions of the tubular goods results in a total stress in the tubular goods equal to the maximum permissible stress for the particular tubular goods.

Another object of this invention is to provide a system for producing an indication whenever the operating conditions of a string of pipe connected between a fixed point and a movable point result in a total stress in the string of pipe equal to the maximum permissible stress for the particular tubular goods, and which system easily can be adjusted for operation with strings of pipe having diiferent maximum permissible stresses.

Another object of this invention is to provide a system which will produce an indication whenever the operating conditions of a string of pipe result in a total stress in the string of pipe equal to a preselected fraction of the maximum permissible stress for the particular pipe being used.

Another object of this invention is to provide a system for indicating the closeness of the angle of deflection of a string of pipe to the maximum permissible deflection angle for a corresponding axial stress.

Another object of this invention is to provide an angle measuring device for directly measuring the total deflection of the string of pipe relative to an axis perpendicular to the deck of the drilling platform.

Still another object of this invention is to provide a single angle measuring device for directly measuring the total angle of deflection of a taut line, which is anchored at one end and has its second end connected to a movable support, relative to a line perpendicular to the surface of the support.

Briefly, the above objects and advantages of this invention are achieved by providing a single angle measuring arrangement which directly determines the total deflection of the tubular member running from the platform into the well, from an axis perpendicular to the deck of the drilling platform and supplies an electrical signal which is related to this deflection. A similar electrical signal is provided for the hook or axial load which is then preferably converted to a signal proportional to axial stress. Both signals are supplied to respective inputs of an X-Y plotter. The respective X and Y elements of the X-Y plotter will then assume a position determined by the instantaneous deflection and axial load or stress of the tubular member. The intercept of the two plotter elements is then compared with a curve which corresponds to the maximum permissible stress for the particular tubing being used and is on a chart mounted on the X-Y plotter. Whenever the locus of the intercept of the two plotter elements approaches the maximum permissible stress curve an indication is given.

The objects and advantages of this invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings, wherein:

FIGURE 1 is a schematic drawing of a floating platform showing the drill pipe and guide lines used for lowering material from the platform to the wellhead;

FIGURE 2 is a side view of the preferred embodiment of the angle measuring arrangement used to directly determine the deflection of the string of pipe.

FIGURE 3 is a schematical diagram of the electrical apparatus used in carrying out this invention; and,

FIGURE 4 is a diagram of one form of indicating circuit which may be used with the apparatus of FIG- URE 3.

Referring now to FIGURE 1 there is shown a Wellhead which is fastened to the ocean floor by any desirable means. Anchored above the wellhead 10 by any suitable anchoring means (not shown) is a floating drilling vessel 12 which may, for example, consist of a floating barge 13 and an elevated platform 14 supported from the top of barge 13 by a plurality of columns 15. Mounted on the elevated platform 14 is a derrick 16 from the top of which is suspended a string of pipe 17, e.g., a drill string, by means of a line 18 and appropriate blocks (not shown). The string of pipe 17 extends through the opening in the rotary table 20 and an opening 21 in the floating barge 13 to the wellhead 10. Coupled to the line 18 is a transducer 22 which provides an electrical signal proportional to the hook or axial load on the string of pipe 17. The transducer 22 may, for example, be a hydraulic sensor which is coupled to the line 18 and produces a hydraulic pressure proportional to the hook load, and a Bourdon tube positioned potentiometer to which the output pressure of the hydraulic sensor is applied and which will generate an electrical signal proportional to the hydraulic pressure.

Connected to the wellhead 10 are a plurality of

guide lines

23 and 24 which are normally used for guiding various pieces of equipment from the drilling vessel 12 to the wellhead 10. The upper ends of the

guide lines

23 and 24 are connected to

tensioning devices

25 and 26, respectively, which apply constant tension to the

guide lines

23 and 24 suflicient to maintain them in a taut condition. The

tensioning devices

25 and 26 may, for example, be winches which are constantly driven through a fluid coupling or other slip arrangement by a prime mover.

As shown in FIGURE 1, the drilling vessel 12 has been displaced to the right with respect to the wellhead 10 and consequently a bending stress has been produced in the pipe string 17 Further bending stresses will be produced in the pipe string 17 due to the pitch and roll of the drilling vessel. In order to determine the magnitude of the total bending stress on the pipe string 17, the total deviation or deflection of the pipe string 17 from an axis normal to the deck of the drilling vessel 12, i.e., the derrick axis, is measured by means of an angle measuring transducer 30 which is coupled to one of the guide lines 24. Since the

guide lines

23 and 24 are always maintained in a taut condition, they are parallel to the longitudinal axis of the pipe string 17 and therefore the angle between the guide line 24 and the axis normal to the deck of the drilling vessel 12 will be the same as the angle between the longitudinal axis of the pipe string 17 and the axis normal to the drilling vessel deck.

Referring now to FIGURE 2, there is shown a preferred embodiment of the angle measuring transducer 30 for directly producing a signal proportional to the total deflection of the pipe string 17 from an axis normal to the deck drilling vessel 12. The angle measuring device 30 is mounted on the deck of the barge 13 by means of a sup port bearing 31 including an outer housing 32 and a hollow bearing shaft 33. The bearing shaft 33 is free to rotate in the housing 32 and is prevented from any axial movement by a shoulder 34 and a locking nut 35. A U-shaped sheave support plate 36 is mounted, e.g., by welding, on the free end of the bearing shaft 33 with the bearing shaft 33 extending through one of the legs 37 of the sheave support plate 36. Supported on the sheave support plate 36 with their axes perpendicular to the surface of the support plate 36 are a pair of sheave support pins 40 and 41 which support sheaves 42 and 43 respectively. The sheaves 42 and 43 are mounted on their respective support pins 40 and 41 by any suitable means which will allow rotation of the sheaves about the support pins but will prevent any movement along the axes of the pins. The support pin 41 is mounted on the support plate 36 along the axis or center line of the support bearing 31 for a reason to be more fully explained below.

Also pivotally supported on the pin 41 is a downward opening U-shaped yoke 44 having its two legs 45 and 46 extending on either side of the sheave 43. Connected between the two legs 45 and 46 at their lower end is a plate 47 in which is mounted a guide bushing 48. The bushing 48 is mounted in the plate 47 such that the axis of the opening in the bushing is aligned tangent to the sheave 43 at its pitch diameter. The guide line 24 extends from the tensioning means 26 through the hollow bearing shaft 33, between the sheaves 42 and 43 and then downwardly through the bushing 48 to the wellhead 10. The geometrical relationship of the sheave 43, the yoke 44 and the bushing 48 insures that the longitudinal axis or centerline of the yoke 44 is maintained parallel to the guide line 24.

As can be seen from the construction of the apparatus of FIGURE 2, any horizontal movement of the vessel 12 relative to the vertical position the guide line 24 assumes when the pipe string 17 is in a vertical position, i.e., the opening 21 of the vessel 12 is directly above the wellhead 10, will result in a pivoting of the yoke 44 either about the axis of the support bearing 31 or about the axis of the sheave support pin 41. Furthermore, any rolling or pitching of the vessel 12 will result in a corresponding movement of the yoke 44 about the axis of the support pin 41 or the axis of the support bearing 31 respectively. Since the sheave pin 41 is mounted on the center line or axis of the support bearing 31, the two axes about which rotation can take place intersect at the pivot point of he yoke 44 resulting in the total angular movement of the yoke 44 being about a single point.

In order to measure the total movement of the upper end of the yoke 44 and hence the total deflection angle of the pipe string 17, a flexible cable 51 is connected to the upper end of the yoke 44 by any suitable means, e.g., a clamp, which will not permit relative movement between the end of the cable 51 and the yoke 44. The free end of the cable passes upwardly through an opening 52 in the drilling platform 14 which is directly above the point of intersection of the axis of the support pin 41 and the axis of the bearing 31, and over a sheave 53 to a linear displacement transducer 19 (FIGURE 1) which may, for example, be a spring reel driven potentiometer. Since any movement of the upper end of the yoke 44 from its position directly beneath the opening 52 will result in a downward pull on the flexible cable 51, the amount of cable 51 pulled down through the opening 52 is directly proportional to the desired deflection angle. The linear displacement transducer 19 will therefore generate a voltage signal proportional to the total deflection angle which, in turn, is proportional to the bending stress in the pipe string 17. It should be noted that in order to make the system as accurate as possible, the distance between the top of the yoke and the bottom surface of the drilling platform 14 and the clearance between the flexible cable 51 and the walls of the opening 52 should be kept at a minimum.

Although in the preferred embodiment the angle measuring device 30 has been described with a single axis of rotation for both the sheave 43 and the yoke 44, it is to be understood the angle measuring device 30 will operate satisfactorily for other positions of the sheave 43. For example, the sheave 43 could be mounted for rotation about an axis which is perpendicular to support plate 36 and which is located along the center line of the support bearing 31 at a point between the support bearing 31 and the support pin 41. Obviously with such an arrangement the bushing 48 would have to extend in the opposite direction from the yoke 44 in order to maintain the center line of the yoke 44 parallel to the guide line 24. It should be noted, however, that such a construction would not be as accurate as the preferred construction at large angles since the parallelism between the guide line 24 and the yoke 44 is not as accurately maintained.

Turning now to FIGURE 3, there is shown a schematical diagram of the circuitry necessary for carrying out the invention. Power for the system is supplied by a regulated DC. power supply 60. Connected to the output of the power supply 60 is a potentiometer 61 which is included in the linear displacement transducer 19 and forms the output circuitry of the angular deflection transducer 30 shown in FIGURE 2. The wiper 62 of the potentiometer 61 is connected to and moves in response to the movement of the cable 51 of the angular deflection transducer 30. The output signal from the potentiometer 61 is then fed to one input, for example the Y input, of an XY plotter 63. Power from the DC. supply 66 is also fed to the hook load transducer 22 which is shown as another potentiometer. The output from the hook load transducer 22 is then applied across a potentiometer or voltage divider 64 which is manually preset according to the size of pipe currently in use and which converts the signal proportional to the hook load to a signal proportional to the axial stress in the drill pipe. The purpose of this conversion will be more fully explained below. The output signal from the voltage divider 64 is then fed to the second or, in the instant case, X input terminal of the XY plotter 63. The plotter stylus 65 will then assume a position representative of the instantaneous value of the deflection angle and the axial stress.

Mounted on the surface of the XY plotter 63 is a chart 66 having thereon a curve 67 which defines the maximum allowable deflection angle for any given axial stress for a given size pipe and a given design or maximum permissible stress. In other words, the curve 67 defines that combination of operating conditions which will result in the total stress in the pipe string 17 being equal to the maximum permissible stress for the particular pipe in use; hence the curve 67 could be referred to as the design or maximum permissible stress curve. At any operating point within the area beneath the curve 67, the total stress in the pipe is less than the design stress while at any point above the curve 67, the total stress in the pipe is greater than the design stress. By noting the position of the stylus 65, the operator can determine how closely the operating conditions approach a critical combination.

Although curve 67 has been plotted in terms of deflection versus axial stress, the curve 67 might equally well be plotted in terms of deflection versus hook load. However, since the hook load signal is merely proportional to the weight or load on the derrick hook and does not take into consideration the cross-sectional area of the particular type of well tubular goods being used, a separate curve representing the critical operation conditions would be required for each size of well tubular goods used. Since the axial stress in the pipe takes into consideration the cross-sectional area of the various sizes of pipe which can be used, a single curve of allowable deflection angle versus axial stress, i.e., a single maximum permissible stress curve, will suflice for all the different sizes and weights of tubular goods which have been designed to a particular value of maximum stress. In order, therefore, to reduce the number of required prerecorded curves 67, the hook load signal is converted to a signal proportional to the axial stress by the adjustable voltage divider 64 which has been calibrated for the various types of well tubular goods to be used. The center tap of the voltage divider 64 is then adjusted to the desired position by the operator according to the particular type of well tubular goods which is being used and before any operating condition measurements are made.

Although the system described in FIGURE 3 will operate satisfactorily, it still requires the attention of an operator in order to determine when the operating conditions approach a critical combination. In order to eliminate the need for constant observation of the XY plotter chart by an operator, the chart 66 is preferably replaced by a char-t 70 as shown in FIGURE 4. The preferred chart 70 consists of an insulating board 71, e.g., plastic, having thereon a conductive layer or coating layer 72 which covers the board in all areas above the allowable deflection angle or maximum permissible stress curve. The chart can be made by etching techniques from copper coated insulating circuit boards. In order to make electrical contact with the conductive layer 72, the convential pen type stylus of the XY plotter is replaced with an electrical contact 73 which is connected in series with the conductive layer 72 through a battery 74 and an indicating device 75 which, for example, may be a horn. Whenever, therefore, the operating conditions of the string of pipe 17 reach a critical combination, the electrical contact stylus 73 will make electrical contact with the conductive layer 72 and energize the horn 75.

Although the system just described will warn the operator that a critical combination of operating conditions has been reached, it is advantageous to the operator to know beforehand that the operating conditions are approaching a critical combination. In order to give the operator this advance Warning, a second electrically conductive layer or segment 76 is also shown on the surface of the board 71 having an edge 77 which corresponds to a combination of operating conditions which will produce a stress which is a selected fraction of the maximum permissible stress. The conductive segment 76 is insulated from the conductive layer 72 by the etched curve 78. Connected to this strip is a second type of warning indicator 79, for example a bell, which will be energized whenever the contact stylus 73 comes into contact with the conductive strip 76.

Obviously, various modifications of the present invention are possible in light of the above teachings. It is therefore understood that the invention is not limited to the particular form illustrated but is capable of embodiment in other forms without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A system for indicating the closeness of the total stress on a string of pipe to the maximum permissible stress for the string of pipe comprising: a platform floating on the surface of a body of water; a string of pipe extending downwardly from said floating platform to a submerged well; a first transducer means mounted on said platform for determining the angular deflection of the string of pipe from an axis perpendicular to the deck of said platform and supplying an electrical output sig nal related thereto; a second transducer means disposed to determine the axial load on said string of pipe and supplying an electrical output signal related thereto; converter means coupled to the output of said second transducer means for converting the signal related to said axial load to a signal related to the axial stress in said string of pipe; an XY plotter, said XY plotter having one of its signal input terminals coupled to the output of said first transducer means and the other of its signal input terminals coupled to the output of said converter means; and, a chart mounted on said XY plotter, said chart having pre-recorded thereon a curve corresponding to the maximum permissible stress curve for the particular pipe being used, whereby the proximity of the resultant plotter indication to the pre-recorded curve is an indication of the closeness of the total stress on said string of pipe to the maximum permissible stress for said string of pipe.

2. A system for indicating the closeness of the total stress on .a string of pipe to the maximum permissible stress for the string of pipe comprising: a platform from which said string of pipe is suspended; a first transducer means disposed to determine the angular deflection of the string of pipe from an axis perpendicular to the deck of said platform and supply an electrical output signal related thereto; a second transducer means disposed to determine the axial load on said string of pipe and supply an electrical output signal related thereto; converter means coupled to the output of said second transducer means for converting the signal related to said axial load to a signal related to the axial stress in said string of pipe; an XY plotter having an electrically conductive stylus, said XY plotter having one of its signal input terminals coupled to the output of said first transducer means and the other of its signal input terminals coupled to the output of said converter means; a chart mounted on said XY plotter, said chart having an electrically conductive coating on the surface thereof adjacent said stylus, with one edge of said electrically conductive coating corresponding to the maximum permissible stress curve for the particular pipe being used; a source of electrical power; and an indicating means connected in series with said stylus, said source of power and said electrically conductive coating, whereby said indicating means will produce an indication whenever the stylus assumes a position proportional to a value of stress equal to or greater than the maximum permissible stress for the particular pipe being used.

3. The apparatus of claim 2 wherein said electrically conductive coating extends along the surface of said chart for all values above said maximum permissible stress curve; a second electrically conductive coating on said surface of said chart, said second conductive coating having its two edges defined by the maximum permissible stress curve and a curve equal to a preset fraction of the maximum permissible stress; and, a second indicating means connected in series with said stylus, said source of power and said second conductive coating.

4. A system for indicating the closeness of the stress on a string of pipe being lowered into a submerged well from a floating platform to the maximum permissible stress for the pipe comprising: first transducer means for determining the deflection of said string of pipe from an axis perpendicular to the deck of said floating platform and producing an electrical signal related thereto; second transducer means for determining the axial load on said string of pipe and supplying an electrical signal related thereto; an X-Y plotter having a pair of input terminals, one of said input terminals being coupled to the output of said first transducer means and the second of said input terminals being coupled to the output of said second transducer means; and, means responsive to the position of the stylus of said X-Y plotter for producing an indication whenever said stylus reaches a position corresponding to the maximum permissible stress for the particular type of pipe being used.

5. A system for indicating the closeness of the stress on a string of pipe being lowered into a well from a platform to the maximum permissible stress for the pipe comprising: first transducer means for determining the deflection of said string of pipe from an axis perpendicular to the deck of said platform and producing an electrical signal related thereto; second transducer means for determining the axial load on said string of pipe and supplying an electrical signal related thereto; an X-Y plotter having an electrically conductive stylus and a pair of input terminals, one of said input terminals being coupled to the output of said first transducer means and the second of said input terminals being coupled to the output of said second transducer means; a nonconductive chart mounted on the surface of said plotter beneath said stylus and in contact therewith; a conductive layer on the upper surface of said chart, said conductive layer covering said chart in all areas above a curve corresponding to the maximum permissible stress curve for the particular pipe being used; a source of power; and, an indicating means connected in series with said stylus, said source of power, and said conductive layer, whereby said indicating means will produce a distinctive indication whenever said stylus reaches a position corresponding to the maximum permissible stress for the partcular type of pipe being used.

6. A system for indicating the closeness of the stress on a string of pipe being lowered into a well from a platform to the maximum permissible stress for the pipe comprising: at least one taut cable leading from said platform to said Well with the axis of said cable being parallel to said string of pipe; first transducer means for determining the deflection of said string of pipe from an axis perpendicular to the deck of said platform and producing an electrical signal related thereto, said first transducer means including a first support means mounted on said drilling platform and disposed to pivot about a first axis, a sheave mounted on said first support means along said first axis for rotation about a second axis normal to said first axis, said taut cable passing over said sheave, a yoke member mounted on said first support member for rotation apout said second axis, bushing means connected to the lower end of said yoke member for engaging said taut cable and maintaining said yoke parallel to said taut cable, and means coupled to the upper end of said yoke and responsive to any movement of the upper end of said yoke for producing an electrical signal proportional to the movement; second transducer means for determining the axial load on said string of pipe and supplying an electrical signal related thereto; an X-Y plotter having a pair of input terminals, one of said input terminals being coupled to the output of said first transducer means and the second of said input terminals being coupled to the output of said second transducer means; and means responsive to the position of the stylus of said X-Y plotter for producing an indication whenever said stylus reaches a position corresponding to the maximum permissible stress for the particular type of pipe being used.

7. Apparatus for sensing the total angular deflection of a taut line that is anchored at one end and has its other end connected to a movable platform comprising: a support means mounted on the deck of said movable plat form; a hollow shaft pivotally mounted in said support means for rotation about a first axis parallel to the deck of said movable platform; a plate connected to one end of said hollow shaft; a sheave mounted on said plate along said first axis, said sheave being mounted for rotation about an axis normal to and intersecting said first axis; said taut line extending over said sheave and through said hollow shaft; a yoke mounted on said plate along said first axis and mounted for rotation about an axis normal to and intersecting said first axis, said yoke extending in opposite direction from its axis of rotation; bushing means connected to the lower end of said yoke for engaging said taut line and maintaining said yoke parallel to said taut line; a flexible cable connected to the upper end of said yoke; a member mounted above the upper end of said yoke, said member being fixed relative to the deck of said movable platform; an opening in said member directly above the point of intersection of said first axis and said axis of rotation of said yoke; said flexible cable extending through said opening; and, means coupled to the free end of said flexible cable for producing an output signal proportional to the movement of the upper end of said yoke.

8. Apparatus for sensing the total angular deflection of a taut line that is anchored at one end and has its other end connected to a movable platform comprising: a support means mounted on the deck of said movable platform; a hollow shaft pivotally mounted in said support means for rotation about a first axis parallel to the deck of said movable platform; a plate connected to one end of said hollow shaft; a sheave mounted on said plate along said first axis, said sheave being mounted for rotation about a second axis normal to and intersecting said first axis; said taut line extending over said sheave and through said 9 hollow shaft; yoke pivotally mounted on the axis of said sheave and extending in opposite directions therefrom; bushing means connected to the lower end of said yoke for engaging said taut line and maintaining said yoke parallel to said taut line; a flexible cable connected to the upper end of said yoke; a member mounted above the upper end of said yoke and fixed relative to the deck of said movable platform, said member having an opening therein directly above the point of intersection of said first and second axes; said flexible cable extending through 10 said opening; and means coupled to the free end of said flexible cable for producing an output signal proportional to the movement of the upper end of said yoke.

References Cited by the Examiner UNITED STATES PATENTS 2,851,880 9/1958 Fiedler 73-141 2,935,368 5/1960 Moseley 34632 3,010,214 11/1961 Postlewaite 33-215 3,121,954 2/1964 Foster 33-1 RICHARD C. QUEISSER, Primary Examiner.

Claims

1. A SYSTEM FOR INDICATING THE CLOSENESS OF THE TOTAL STRESS ON A STRING OF PIPE TO THE MAXIMUM PERMISSIBLE STRESS FOR THE STRING OF PIPE COMPRISING: PLATFORM FLOATING ON THE SURFACE OF A BODY OF WATER; A STRING OF PIPE EXTENDING DOWNWARDLY FROM SAID FLOATING PLATFORM TO A SUBMERGED WELL; A FIRST TRANSDUCER MEANS MOUNTED ON SAID PLATFORM FOR DETERMINING THE ANGULAR DEFLECTION OF THE STRING OF PIPE FROM AN AXIS PERPENDICULAR TO THE DECK OF SAID PLATFORM AND SUPPLYING AN ELECTRICAL OUTPUT SIGNAL RELATED THERETO; A SECOND TRANSDUCER MEANS DISPOSED TO DETERMINE THE AXIAL LOAD ON SAID STRING OF PIPE AND SUPPLYING AN ELECTRICAL OUTPUT SIGNAL RELATED THERETO; CONVERTER MEANS COUPLED TO THE OUTPUT OF SAID SECOND TRANSDUCER MEANS FOR CONVERTING THE SIGNAL RELATED TO SAID AXIAL LOAD TO A SIGNAL RELATED TO THE AXIAL STRESS IN SAID STRING OF PIPE; AND X-Y PLOTTER, SAID X-Y PLOTTER HAVING ONE OF ITS SIGNAL INPUT TERMINALS COUPLED TO THE OUTPUT OF SAID FIRST TRANSDUCER MEANS AND THE OTHER OF ITS SIGNAL INPUT TERMINALS COUPLED TO THE OUTPUT OF SAID CONVERTER MEANS; AND, A CHART MOUNTED ON SAID X-Y PLOTTER, SAID CHART HAVING PRE-RECORDED THEREON A CURVE CORRESPONDING TO THE MAXIMUM PERMISSIBLE STRESS CURVE FOR THE PARTICULAR PIPE BEING USED, WHEREBY THE PROXIMITY OF THE RESULTANT PLOTTER INDICATION TO THE PRE-RECORDED CURVE IS AN INDICATION OF THE CLOSENESS OF THE TOTAL STRESS ON SAID STRING OF PIPE TO THE MAXIMUM PERMISSIBLE STRESS OF SAID STRING OF PIPE.