Offshore oil rigs are dangerous places. Hammered by heavy seas and subject to a whole variety of forces, oil platforms and associated equipment need to be monitored constantly to keep both the workers and the infrastructure safe.
Two separate articles in Offshore Engineer magazine gave examples of the ingenuity of engineers in solving complex problems involving serious heavy equipment – with load cells at their heart.
Wellhead fatigue issues
The first article concerns the dangers of wellhead fatigue. When older oil wells need to be decommissioned or re-entered, the operation usually involves older equipment being paired with more modern technology. However, in the case of wellheads, the fitting of a modern, robust blowout preventers (BOP) and risers can put a lot of strain on the older wellhead in terms of weight and movement.
Trendsetter Engineering devised a system that tethered the BOP to piles driven into the seabed, reducing the movement and thus reducing the wear and tear on an already-aging wellhead.
Each BOP has a connecting point (known as a thimble) for the end of the mooring line (known as a fairlead). A load cell is located at the thimble to monitor the load on the mooring line, which is made of two different types of Dyneema rope depending on the load requirements. The combination of the BOP and a new Pile Top Assembly (PTA), when held firmly in place and monitored by load cells, is estimated to improve the wellhead’s fatigue life by a impressive factor of 1000.
Load cell calibration for oil platform legs
For safety of all working on board, regular checks are required on a standard design of oil platform known as the Tension Leg Platform, or TLP. Tension leg platforms have been in use since the mid 1980s, and are usually deployed where water is deeper than 5200ft. One of the major safety checks for TLPs is that the tendons that secure it to the sea bed are kept at the correct tensions. This is where the load cells come in.
Legs, load cells and lifting
In the example cited in the article, the Snorre A TLP in the Norweigian North Sea has 16 load cells per leg. Like all load cells, the load cells fitted in the leg require regular calibration. Calibration involves taking the weight of the entire platform off the load cells to recalibrate them. Not an easy task in the North Sea!
In the past, load cell recalibration involved using two 530 tonne capacity hydraulic cylinders to lift the platform up 21mm, taking the weight off the load cells. The problem was that the cylinders had to be moved from one leg to another and between load cells for separate calibration, not an easy task when each cylindersweighs around 400kilos.
A long time coming
The best solution took six years to find, but now each load cell has its own dedicated cylinder which can be placed in the leg. This enables inspectors to test and calibrate all 16 load cells at once. What’s more, by using a bespoke-built, double-acting cylinder in combination with a lowering control panel, each leg could be repositioned onto the load cells more gently, reducing impact shock.
Now, each calibration session involves just eight separate lifts rather than the former 32, and there is no requirement to move heavy equipment from one leg to another.
Smart solutions at sea and on land
At Richmond Industries, we are always working to help clients solve problems or create new solutions using load cells. We’re also happy to work with other service suppliers to create integrated solutions for unusual issues.
So, why not put us to the test? if you have a particular load cell related challenge, call us. We can create innovative, practical solutions using both standard and bespoke load cells, manufactured to order here at our Reading HQ.