A load cell is an accurate tool in a sterile laboratory setting. It is an oasis in the depths of the North Sea or on the salt-covered decks of an offshore oil platform.
Although the overall principles of strain gauge technology, the transformation of mechanical force to a measurable electrical signal, are well-known within the engineering fraternity, the practical implementation of such sensors is hardly a textbook subject.
The point is that in the case of industries such as offshore energy, underwater construction, and aerospace testing, it is not only necessary to measure weight but to remain within the +-0.03% accuracy range, but at the same time resist the onslaught of galvanic corrosion, extreme hydrostatic pressure, and violent mechanical vibrations.
With the increasing needs of energy infrastructure taking the infrastructure further into the water, the load cell has ceased to be a mere measuring device, but a vital part of Structural Health Monitoring (SHM).
Subsea Mooring and Tension Leg Platforms (TLPs)
In order to see the high-standard features of the modern load cells, we need to refer to the Floating Production Storage and Offloading (FPSO) ships and the Tension Leg Platforms (TLP), which prevail in the offshore oil and gas industry.
These huge buildings are attached to the sea floor through mooring cables or vertical tendons. These lines are in a state of tension that is immense. When the tension is too small, the platform drifts, and there is a danger of the high-pressure riser pipes transporting oil to the surface rupturing. In case tension is excessive, the tendons of the steel can become exhausted, and the structural snap is bound to be disastrous.
Within this environment, Standard load cells do not last more than a few weeks. It is used in conjunction with a specific type of sensor, the Subsea Bolt or Load Pi,n which typically is part of the mooring shackles or riser tensioning system.
1. The Challenge of Hydrostatic Pressure and Hermetic Sealing
At depths of 3,000 meters, the pressure is roughly 300 times that of the surface. A standard load cell housing would implode, or at the very least, the pressure would distort the spring element (the metal body of the sensor), causing a zero shift that renders the data useless.
Recent higher-end load cell designs in this type of environment use either pressure-compensated designs or ultra-thick 17-4 PH Stainless Steel or Inconel housings. They are not just water-resistant but hermetically welded using laser welding to make them. All cable access points constitute a possible point of failure and necessitate glass-to-metal seals to avoid wicking, whereby a water molecule travels through the wiring of the insulation of a cable to the inner electronic components.
2. Signal Integrity Over Long Distances
Within an offshore setting, the separation between the load cell (underwater 100 meters below the hull) and the control room (the bridge) may be hundreds of meters. The typical signal of a load cell in millivolts per volt (mV/V) in analogue mode is very vulnerable to electromagnetic interference (EMI) from the huge generators and massive motors of the ship.
The industry standard has shifted toward Integrated Digitisation. High-standard load cells now often feature internal amplifiers that convert the signal to a 4-20mA current loop or a digital protocol like RS-485 (Modbus) or CANopen. By digitising the data at the point of measurement, the system eliminates the noise of the environment, ensuring that a 500-tonne reading on the seabed is reflected accurately on the operator’s screen.
Case Study – The Heavy Lift Manoeuvre
In addition to the inactive surveillance, load cells are the brain of the offshore heavy-lift cranes. Where a heavy lift ship (e.g. the Sleipnir) is trying to place a 10,000 tonne topside block onto a jacket structure, there is no room to spare.
The Snatch Load Risk – As the sea rises and falls, the ship goes up and down. When the crane commences a lift when the ship falls into a wave gully, the dynamic load, the abrupt jerk on the cable, may increase the weight supported by the boom of the crane, many times over, in a fraction of a second. This is known as a snatch load.
In the given application, the crane blocks have the load cells embedded in the Sheave Pins. They should be capable of high frequency response (the capability to sample data thousands of times per second) in order to see these microsecond spikes in tension.
This real-time data is fed to the control system to switch on Active Heave Compensation (AHC), winch systems that automatically pay out or haul in cable to, in turn, reverse the movement of the waves to make the load stationary with respect to the bottom of the sea.
The Material Science of Reliability – Why Alloy Selection Matters
General knowledge suggests that steel is strong. In the specific environment of the splash zone (where the structure is alternately wet and dry), standard carbon steel is a liability.
High-performance load cells prioritise materials like:
- 17-4 PH Stainless Steel – Offers a unique combination of high strength and excellent corrosion resistance.
- Electroless Nickel Plating – Applied to sensors in less corrosive but high-wear environments to prevent surface pitting.
- Duplex Stainless Steel – Used in high-salinity subsea applications where pitting and crevice corrosion are the primary enemies.
Redundancy – The Dual-Bridge Requirement
One is none in critical infrastructure, and two is one. In case of aerospace structural testing or offshore mooring, a load cell failure does not imply a stop.
Dual-Bridge Load Cells are used in high-standard applications. Both sets of strain gauges and two sets of Wheatstone bridge circuits are housed in one sensor body in these units. When one circuit is faulty, the cable is broken or has shorted internally, the other circuit still supplies data. In a full-size aircraft aerospace Iron Birds test, in which a full-size wing of an aircraft is load-tested to the point of destruction, this redundancy can eliminate the possibility of a million-pound test being spoiled by the failure of a single sensor.
Conclusion
The trend in the UK’s tech and industrial sectors is moving toward Smart Load Cells. We are entering an era where a sensor doesn’t just report weight; it reports its own health.
To be future-proof, load cells now have internal event logging, where each time the sensor was overloaded or exposed to temperature values outside its compensated range, the event is logged. This makes it possible to do Predictive Maintenance, where a sensor is replaced before it can reach a state of structural compromise, instead of responding to one.
To the visitors of TechKTimes, the message is obvious – the contemporary load cell is no longer an outer-ring device. It is the raw material that allows the most complicated engineering projects on the planet; it can be the ocean floor trench or the space race of the newcomers.
