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DayPaper No.

Conference paper sponsored by

BARCELONA, SPAINOrganised by the ABR Company Ltd

INTRODUCTIONOf interest to the petroleum tanker industry is a synthetic replacement of the Emergency Tow-Off Pendant (ETOP), commonly referred to as a ‘fire wire’. Its purpose is to provide a means for tugs to tow a ship away from the dock in the event of a fire. Wire rope is currently used in this application, but the handling of these heavy wire ropes has resulted in many injuries to deckhands. Vulcan, a patented fire-resistant synthetic rope, has been developed as a synthetic alternative that is significantly lighter and eliminates the issues with ‘fish-hooks’, which are the broken wires that protrude from the wire rope that result in hand injuries. Maintenance costs are also reduced when using synthetic ropes in comparison with wire ropes.

In late 2009, the Oil Companies International Marine Forum (OCIMF) released new recommendations regarding Emergency Tow-Off Pendant Systems (ETOPS) which was the result of a risk assessment performed by Lloyds Register1,2. The outcome of this risk assessment was: “…it is recommended that ETOPS be eliminated from general use and that they should not be generally considered essential equipment for vessel safety”. With the publication of the Lloyds Risk Assessment, the OCIMF’s position is “that ETOPS are not required and have not provided benefit in the past. If individual marine terminal risk assessments or

port authorities still require ETOPS, though, there may be other options to pursue other than wire rope”.

Samson’s development of a synthetic ETOP, Vulcan, and its ability to handle severe heat and open flame, are presented here to demonstrate that a synthetic fibre rope made of Technora® fibre using a proprietary fire-resistant coating can meet the OCIMF required breaking strength, even after exposure to flames and a high-temperature environment.

Currently, there are no defined fire resistance performance requirements for ETOPs, for either wire or synthetic, other than the new rope break strength. Since no testing standards or high heat performance requirements exist, Samson has developed a set of testing parameters with which to compare synthetic to wire.

FIBRE SELECTIONThe starting point in developing any rope product is to identify what fibres are available that would meet the performance requirements for the application. The chosen fibre for this application is a p-aramid. This selection was due to the need for a fibre that was heat resistant and able to retain the desired properties at elevated temperatures. A p-aramid fibre has the following desirable characteristics:

High Temperature Resistant Rope

SYNOPSISWith the critical high temperature and engineering properties intrinsic to aramid fibres, rope manufacturers have been using them with great success in a variety of applications. However, aramid-fibre ropes by themselves cannot withstand direct flames, which is a requirement in some applications. In response to the petroleum-shipping industry’s need for a synthetic Emergency Tow-Off Pendant also known as ‘fire wire’, Samson, Teijin Aramid, and Passive Fire Protection Partners have worked together to produce a high-temperature resistant rope which, when combined with a specialised coating technology, can replace fire wires in high-heat environments, including direct flames. This paper will give an overview of the high-temperature resistant rope developed for the petroleum shipping industry that is being used in the field to tow tankers away from terminals by tugboats in cases of emergency. It will also discuss the advantages of the product as it is used in this application and provide observations made about the product’s performance in field trials.

Danielle Stenvers (speaker/co-author), Rafael Chou (co-author), Samson, USA

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• Higher initial tenacity at elevated temperatures;

• Good heat cycling properties;• Good abrasion properties;• Good chemical resistance;• Not affected by hydrolysis.

For emergency tow-off pendants, the obvious requirement is the ability to withstand heat for an extended time period. However, in addition to having good strength properties at elevated temperatures, p-aramid fibres also have the ability to retain strength when exposed to higher temperatures for extended periods of time. Figure 2 shows the typical strength decay curve of p-aramid fibres when exposed to elevated temperatures for a period of one hour. Technora fibre is chosen over other aramids due to its higher initial strength and better long-term strength performance when exposed to heat.

ENHANCING FLAME RESISTANCEThe flame resistance property of aramid fibres can be further enhanced by utilising specialised fire-resistant (FR) coatings. The coating’s special intumescent property provides maximum protection to the rope by expanding to form a high-density char that acts as insulation when it is exposed to fire or high heat. This enables the rope to retain more of its strength for a longer period of time.

To demonstrate the importance of fibre selection as well as the performance enhancements of using a fire-resistant coating, testing was performed on 12mm diameter ropes, which were subjected to direct flame contact from a propane torch. Figure 3 (right) demonstrates the test setup and Table 1 shows the results of this testing and the clear advantage of the FR coating. The uncoated Technora fibre survives 12 minutes with direct contact from the propane torch before it fails. This time to failure increases more than five times with the addition of the FR coating. However, this test also demonstrates the need for the base fibre to have high heat resistance properties on its own. Dyneema®, nylon and polyester fibres all have melting points below 260 degrees C.

Fibre Type Uncoated FR Coated Technora® 12 min 65 min Polyester <1 min 1.75 min Nylon <1 min 1.5 min Dyneema® <1 min <1 min

Table 1: Time until failure during 750-degree C open-flame test on coated and uncoated ropes.

Figure 3: Test setup for direct flame testing.

HEAT AND FLAME RESISTANCESince there are no industry standards for heat or flame testing and performance requirements for ETOPs, Samson developed the following procedures to determine the effect that heat or flame exposure has on rope and wire in a potential real-world scenario.

Heat TestingSpecial equipment was fabricated to perform these tests, as shown in Figure 4. A heated cylinder was installed in a test bed and the rope pulled through

Temperature (oC)

Bre

akin

g S

treng

th (N

)

450

400

350

300

250

200

1500 50 100 150 200 250

Technora T200

Twaron 1000

Figure 1: p-aramid tensile properties at elevated temperatures.3

Technora T200

Twaron 1000

150 200 250 300Exposure Temperature (oC)

Ret

aine

d S

treng

th a

t 200 C

(%)

60

70

80

90

100

110

Figure 2: p-aramid tensile properties after a one-hour exposure.4

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without direct contact of the rope and the heat source. The heat test consisted of the following conditions:• A 300-degree C temperature oven;• 30 minutes exposure of the rope to the heat source

while loaded to 20 per cent of break strength; • The rope was broken while still at temperature

(300 degrees C).

Figure 4: Special equipment for heat testing.

Initial testing in this heat chamber was performed on small-scale ropes (24mm diameter) with various constructions and coatings to determine the best options for the final product development. Testing was performed on the following:

24mm diameter Coating UsedWire (6x36 EIPS IWRC) None12-strand single braid Fire-resistant (FR)Jacketed rope Polyurethane (PUR)Jacketed rope Fire-resistant (FR)8x3-strand single braid Fire-resistant (FR)

In small-scale testing of various rope constructions, the results show:• The jacketed construction outperformed single braid

ropes, which is a result of the increased insulation that protected the core (the strength member);

• A jacket only provides a slight delay in the heat transfer;

• The same jacketed rope construction with fire-resistant (FR) coating retained a higher strength than the standard polyurethane (PUR) coating;

• Wire rope also shows about a 12 per cent reduction in strength due to heat exposure.

The results shown in Figure 5 are a ‘worst case scenario’ since heat transfers more quickly through a smaller diameter rope than a larger diameter rope. As the diameter increases, the strength loss will be minimised. Based on actual test data and known fibre properties, we are able to model the strength loss under these specific heating conditions and provide ropes that will meet OCIMF strength requirements even after heat exposure.

Flame TestingThe intent of the flame testing was to determine the amount of damage the rope may experience if it were subjected

12-strand rope.

8x3-strand rope.

Jacketed rope.

Figure 5: The retained strength of 24mm diameter ropes of varying coatings and constructions after 30 minutes exposure to 300 degrees C at 20 per cent load.

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to an explosion onboard a vessel. Specialised testing equipment was prepared for this test application as illustrated in Figure 6, above. This equipment provided direct exposure to the rope from an open flame in a controlled setting. The flame test consisted of the following conditions:1. Direct exposure to a 600-degree C open flame for

10 seconds, then,2. Tested for tensile strength at room temperature.

Initial testing in this setup was performed on small-scale ropes (24mm diameter) with various constructions and coatings, the same constructions that were tested in the heat chamber, to determine the best options for the final product development. In small-scale testing of various rope constructions, the results show:• No significant strength loss for wire, 12-strand, or

jacketed constructions;• The 8x3 strand is most affected by the flame due to

the larger surface area of the strands.

Figure 7: Retained strength of 24mm diameter ropes of varying constructions and coatings after 10-second direct exposure to a 600-degree C flame.

APPLICATION MODELLINGBoth fibre and rope testing were performed to help build a model to estimate rope performance as the scale up to larger rope sizes occurred.

Fibre strength properties are used as the baseline and are measured before and after exposure to high temperature. Tables 2 and 3 model the system properties of both wire and Technora fibre. Wire, as expected, has a higher retained tensile, but the fibre does still retain approximately twice the recommended working load (assuming a working load of 20 per cent of the break strength) over the same time period.

Measured at 20°C

Measured at 300°C

Measured at 300°C

(after 30 min at 300°C)

Break strength (GPa) 2.37 1.8 1.74Retained strength (GPa) 100% 75.9% 73.4%Density (kg/m3) 7600 7600 7600 Table 2: Wire System model.

Measured at 20°C

Measured at 300°C

Measured at 300°C

(after 30 min at 300°C)

Break strength (GPa) 3.42 1.5 1.5Retained strength (GPa) 100% 43.9% 43.9%Density (kg/m3) 1390 1390 1390 Table 3: Technora System model.

Using the flame test setup shown in Figure 6, an 18mm diameter, 12-strand Technora rope was subjected to direct flame contact and the internal temperature of the rope was measured over a period of 60 seconds. Figures 8 and 9 (opposite) show the effect of coatings on the heat transfer rate, as well as the significant difference between the internal rope temperature and the actual flame temperature. While the flame temperature was 600 degrees C, the internal temperature of the rope after 60 seconds remained less than 200 degrees C. The PUR-coating actually has the highest internal temperature and both the uncoated and PUR-coated ropes are approximately 10-20 degrees C higher than the FR-coated rope.

This data, in combination with the Technora fibre properties and the heat and flame testing performed on the 24mm diameter ropes, allows a model to be built to

Figure 6: Flame test room setup with six propane torches surrounding the circumference of the rope.

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estimate the rope temperature under certain conditions and how that temperature affects the overall strength of the fibre and hence the strength of the rope.

Larger diameter ropes have also been tested and validate the model for the strength estimations after being subjected to heat and load.

VULCAN: SYNTHETIC ETOPFrom this study the conclusion can be drawn that a rope produced from Technora fibre, along with a specialised FR-coating can replace wire rope in high heat applications. The best performing construction was a jacketed rope with FR-coating applied to the strength member (core), which has been developed into Samson’s product called Vulcan. The synthetic ETOP is made of Technora fibre in conjunction with a proprietary fire-resistant coating and meets the OCIMF required breaking strength for ETOPS5, while achieving a 70-80 per cent weight saving over wire. Table 4 (above) provides a comparison between wire and Vulcan with regard to the OCIMF minimum breaking strength requirements.

Due to some strength being lost when Vulcan is exposed to high temperatures, the user may choose to use a larger diameter rope so that its retained strength will still meet the required break strengths even when operating under severe heat or flame conditions. Ropes at these sizes were tested at 300 degrees C after being held at 20 per cent of their break strengths for 30 minutes at the same temperature (see Table 5). Note that the wire sizes are larger here than in Table 4. This is due to the strength loss that is also observed in wire when exposed to the same high temperature testing parameters as the synthetic rope.

CONCLUSIONSTesting has demonstrated that Technora fibre has the ability to withstand and perform under high temperatures. An FR-coating is necessary to resist damage from direct flame contact and to provide thermal insulation. When compared to wire rope of equal diameter, a jacketed rope made of Technora fibre with FR-coating can still exceed the recommended working load after exposure to a high temperature environment. Upsizing to a slightly larger diameter

Figures 8 and 9: Increase in internal rope temperature with 600-degree C flame.

Vessel size

(kDWT)

Min. break strength

requirement (tonnes)

Wire diameter

(mm)

Vulcan diameter

(mm)

Wire weight

(per 100m)

Vulcan weight

(per 100m)

Weight savings

over wire

< 20 30 tonnes 22mm 24mm 211kg 44.6kg 0%20 – 100 55 tonnes 28mm 32mm 348kg 103kg 70%

100 –300

100 tonnes 36mm 46mm 619kg 186kg 70%

300+ 120 tonnes 40mm 52mm 728kg 222kg 70%

Vessel size

(kDWT)

Min. break strength

requirement (tonnes)

Wire diameter

(mm)

Vulcan diameter

(mm)

Wire weight

(per 100m)

Vulcan weight

(per 100m)

Weight savings

over wire

< 20 30 tonnes 22mm 30mm 211kg 92kg 57%20 – 100 55 tonnes 30mm 42mm 430kg 160kg 63%

100 –300

100 tonnes 40mm 56mm 726kg 250kg 65%

300+ 120 tonnes 44mm 60mm 844kg 286kg 65%

Table 4: Vulcan vs wire: meeting OCIMF minimum breaking strength requirements prior to heat exposure.

Table 5: Vulcan: Rope sizes to meet OCIMF strength requirements after heat exposure.

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will allow a rope of Technora fibre to equal the performance of wire rope after exposure to a high temperature environment, while still maintaining a significant weight savings.

REFERENCES1 Lloyd’s Register Risk Assessment of Emergency Tow-off Pennant Systems (ETOPS) onboard Tank Vessels, Oil Companies International Marine Forum (OCIMF), London, October, 2009. 2 Recommendations for Alternatives to Traditional Emergency Tow-off Pennants, Report of the Working Group, OCIMF, London, July, 2010.3 p-Aramid Tensile Properties at Elevated Temperatures, Teijin, 2009.4 p-Aramid Retained Strength After 1–Hour Heat Exposure, Teijin, 2009.5 International Safety Guide for Oil Tankers and Terminals (ISGOTT), 5th Edition. OCIMF, Institute of Chartered

Shipbrokers (ICS), International Association of Ports and Harbors (IAPH), Livingston, 2006. (not referenced in text) Mooring Equipment Guidelines, 3rd Edition, Livingston, 2008.

PATENTS (not referenced in text)1. Chou C T, et al, High Temperature Resistant Rope Systems and Methods, US Patent 7,168,231, 30th January, 2007.

2. Chou C T, et al, High Temperature Resistant Rope Systems and Methods, US Patent 7,437,869. 21st October, 2008.

3. Chou C T, et al, High Temperature Resistant Rope Systems and Methods, US Patent 7,743,596. 29th June, 2010.

ACKNOWLEDGEMENTSThe authors gratefully acknowledge the participation and assistance of Teijin Aramid, Passive Fire Protection and Southwest Ocean Services.