Safety is crucial in mooring operations – and the right mooring lines for the right environment help ensure it. But conventional HMPE ropes lose significant strength at temperatures above 50 °C – meaning their safety cannot always be guaranteed. Vessel managers need more reliable mooring line materials that won’t fail, even in extremely hot conditions. Mooring lines based on aramids, such as Twaron® and Technora®, are a strong solution, delivering low creep at high temperatures – and therefore, improved safety levels.
The right mooring solution for the right climate
Choosing the right mooring lines for the right environment is crucially important – the safety of mooring line operators depends on it. Indeed, although they are often unreported, mooring accidents – caused by a mooring line snapback or unexpected tightening – are a serious issue within the shipping industry.
HMPE mooring lines were introduced as a safer alternative to steel wire ropes, which are brittle and have a tendency to break. Indeed, these high-performance ropes perform very well in cooler ambient conditions.
However, HMPE ropes lose significant strength around 50 °C. This means their reliability and safety cannot always be guaranteed. Indeed, HMPE mooring line failures have already had serious consequences: in 2015, among other incidents, a deck officer on the Zarga LNG carrier suffered severe head injuries when he was struck by a parted HMPE mooring rope during a berthing operation.
Low creep under heat: The key to safety
HMPE’s strength loss at high temperatures is a result of its poor creep performance. Specifically, tests at Teijin Aramid’s Research & Innovation Center have shown that, at higher loads and temperatures, HMPE will slowly soften and elongate. This can lead to premature creep rupture and breakage.
This creep performance is particularly concerning given the typical climates of the shipping industry. Mooring lines are heavily used by liquified natural gas (LNG) carriers operating in very warm countries such as Australia, Saudi Arabia, Qatar, and the United Arab Emirates. In these regions, the temperature of mooring lines on deck can easily reach 50°C and above.
To keep deck crew safe and prevent further accidents from happening, the marine industry needs alternative mooring line materials. Aramid fibers, such as Teijin Aramid’s Twaron® and Technora®, can provide a solution to many of the marine industry’s safety challenges. Like HMPE, these fibers have excellent flexibility and strength-to-weight ratios, making them easier and safer to handle than steel wire ropes.
However, unlike HMPE, aramid has very low creep, so it hardly elongates during use over time. This reduces the risk of breakage, enabling aramid-based mooring ropes to remain safe even at extremely high temperatures.
Testing high-temperature performance: Aramid vs HMPE
To test the performance of mooring lines in real-world conditions, such as at elevated temperatures, and confirm the superior performance of aramid to its customers, Teijin Aramid decided to conduct its own testing program at its Research & Innovation Center (RIC).
The results of the tests show that HMPE ropes perform satisfactorily at room temperature. However, at higher temperatures, the aramid mooring lines remained intact, while the HMPE ropes showed reduced strength.
Initially, ropes made of Twaron®, Technora®, and HMPE were tested at 50°C and 70% minimum breaking load (MBL) for 100 hours. If they passed this test, no further tests were done. If they failed, a longer, lower-temperature test was conducted at 40°C and 50% MBL for up to 400 hours.
Specifically, the Twaron® and Technora®-based ropes that were tested survived a 70% minimum breaking load at 50°C for 100 hours, showing only minimal creep. In contrast, HMPE ropes failed after about ten minutes under the same conditions, as shown in the graph below:
Enabling safer mooring operations worldwide
These properties mean aramid mooring lines can enable safer mooring operations in hot environments, protecting deck crews and providing peace of mind for vessel managers and mooring line operators alike.
“As well as the lower chances of creep rupture, aramid’s stable performance over time independent of temperature also means more predictable behavior, an additional contribution to safety,” adds Huib Kwint, Global Technology & Application Manager. “So far, across the world, we haven’t heard of any fiber-related safety accidents in aramid-based mooring lines.”
What’s more, the safety levels enabled by aramid also enable manufacturers of mooring ropes to follow safety recommendations, such as those in the latest Mooring Equipment Guidelines (MEG4), more easily. “The MEG4 now advises additional measures for synthetic fiber ropes,” notes Kwint. “At Teijin Aramid, we always recommend complying with these guidelines – using aramid enables manufacturers to achieve the highest levels of safety without having to meet extra requirements.”
Aramid ropes: The safer way forward in hot climates
Thanks to these key safety advantages, increasing numbers of rope manufacturers are likely to choose aramid for their mooring lines over steel or HMPE in the years to come.
“As the coal-to-gas transition progresses and LNG carrier shipping volumes increase, it’ll become even more important to ensure safe mooring operations,” adds Kwint. “In the extremely hot regions where these vessels operate, that means temperature-resistant mooring lines.”
And, with global warming leading to rising temperatures around the globe, this need is likely to become even more urgent. One thing is clear: aramids like Twaron® and Technora® are the safest choice for the demanding conditions created by high temperatures.
Get in touch with our experts
Looking to enhance your mooring line product development and add real value to your customers? To request a sample rope of Technora®, or learn more about its beneficial properties in mooring lines, please get in touch with our expert Satyavan Hange (Global Market Manager Ropes & Cables) or visit the Mooring line application page.
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Satyavan HangeGlobal Market Manager Ropes & Cables