Exploration • Drilling • Field Services
Load pins for critical load measurements Steve Hewitt looks at the uses of load measuring pins within the oil industry. W
ithin the oil industry load measuring pins are widely used – from drill rigs, supply boats and sub-sea assemblies. Tey can also be used to replace an existing
joint where clevis pins are used in cranes, winches, anchor chain stops, wedge sockets and shackles. Te material from which pins are manufactured is, in the main, high strength stainless steel and sometimes a super alloy (Fig. 1). Strain gauges are used to measure the shear strain at the maximum shear section through the pin and arranged into a whetstone bridge circuit. By using the shear stress, the measurement is not dependant on load position and the supports as bending effects have very little impact on the measurement. To help with this, 3D modelling is used which is then linked to a finite element analysis (FEA) package. With the use of the FEA, stresses in the pin are revealed and this allows for modifications to be carried out before the material is cut. Te 3D modelling also enables the product to be visualised before final drawings are completed (Fig 2). Te load pin can also measure loads in more than
one direction and with monitoring in two plains, X and Y. Te output from the strain bridge generally varies as the angle of the applied load rotates around the central axis by the cosine law and so, with a single applied bridge at 90 degrees, the output has reduced to zero. By installing a dual bridge offset by 90 degrees, it is possible to have two signals from the pin, which can be used to determine the resultant force and angle. Tis format of pin can be used on variable angle jib cranes without adding extra steelwork to give a constant effective angle over the pin. By having the loads in both plains, the resultant load can be calculated, and by referring one of the plains to a known angle the direction of load can be calculated. We also know that strain gauges can be classified as simple apparatus and this makes it easier to use in hazardous areas with the use of the correct electronics.
Applications for load pins With anchor handling using the winches, load pins can be installed in the brake mechanism for static load measurement or in the base of the winch for dynamic measurements.
Tere are so many variations with winch design and elements required from the operator that each case is considered individually.
Fig. 1. Typical load pins.
Mooring buoys are another application where load pins are used to measure the hawser tension. Tis application is critical for safety as well as to try to predict the life of the hawser.
Chain stoppers for tankers and tugs include pins that can also be monitored to control forces. Diving equipment requiring load monitoring often use load pins as a practical way to monitor load. Drill string tension and heave compensation use load pins as a method to capture the load.
Future developments As knowledge of materials and designs develop, the load measuring pin improves in accuracy and predicted life. Associated electronics are also making it easier to measure loads that were, in the past, difficult but can now be continually monitored. ●
Enter 23 or ✔ at
www.engineerlive.com/iog
Steve Hewitt is Director, Active Load Limited, Reading, England.
www.activeload.co.uk
www.engineerlive.com 23
Fig. 2. 3D modelling also allows load pins to be visualised before final drawings are completed.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80