Shipboard thermal-oil lines protected with cellular glass insulation

The thermal-oil pipeline for Rigel Shipping's Diamond Star tanker wends through other ship piping from the bow (Fig. 1).

Installation of the cellular glass insulation to a vessel's thermal-oil pipeline progresses as Rigel Shipping's three vessels all retrofitted to new pipelines and Foamglas Super K insulation in 1998 (Fig. 2) [27,835 bytes]
Thermal-oil pipelines aboard vessels operating in eastern Canadian and U.S. waterways have been coated with a cellular glass insulation to protect against the often frigid and corrosive environment.

Rigel Shipping Canada Inc., Shediac, N.B., operates a fleet of petroleum ships throughout the eastern waterways of Canada and the U.S. The company primarily transports petroleum products, heating oil, and some chemical products for such companies as Exxon Corp., Shell Oil Co., Ultramar Corp., and Imperial Oil Ltd.

Built side-by-side during 1992-93, each double-hulled ship in the three-vessel, Canadian-flagged fleet-Emerald Star, Diamond Star, and Jade Star-measures 405 ft by 58 ft, displaces 10,500 dwt, and is built to last 20 years or more.

At the heart of each vessel, running on the main weather deck from the bow to the accommodations superstructure, is a thermal-oil pipeline (Fig. 1), ranging from 2 to 6 in. OD.

The 600+ ft pipeline supplies thermal heating medium for warming the liquid cargo in the ship's 12 storage tanks. The high viscosity of some cargoes requires them to be heated and circulated constantly, says Rigel Shipping, and that places a high degree of reliance on the piping insulation system.

With the aid of heat exchangers, the thermal-oil system is designed to function at 356° F. (180° C.) at the burner outlet, despite the climatic and environmental conditions indigenous to the fleet's operations area from Arctic waters to the Gulf of Mexico.

With a properly maintained heat-delivery system, the company says, the viscous cargoes can be maintained at a temperature of up to 140° F. (60° C.) during transit.

Moisture intrusion

Rigel Shipping says there are several environmental and operational threats to the ships' piping and its protective insulation. Foremost is the problem of water intrusion and possible ice formation.

The harsh environment exposes the vessels' thermal-oil piping systems to rainwater, salt water, moist ocean air, high humidity, and frigid temperatures. These conditions can break down the insulation and affect the heat transfer and, thus, the viscosity of the oil.

Also, once moisture enters the insulation and becomes trapped, it can lead to corrosion of piping systems. Therefore, says the company, a nonabsorbtive insulation is critical to maintaining proper heating temperature and preventing pipe corrosion.

When first built, the thermal-oil pipelines of Rigel Shipping's vessels were insulated with mineral wool. But company personnel soon realized that the mineral wool was absorbing substantial moisture.

And after only 3 years' service, the mineral-wool insulation had failed completely. Leaks were detected in the piping system, and petroleum products were spilling onto the deck.

It was clear that the thermal-oil line had suffered complete corrosion. Patching one leak only would cause the pipe to leak elsewhere, says the company. The only solution was to replace the entire pipeline and choose a more protective, nonabsorptive insulation.

Nonflammable insulation

After choosing a heavier grade steel for its thermal-oil pipeline, Rigel Shipping began researching insulation options and eventually selected Foamglas Super K insulation.

This operates over a broad range -450° F. to 900° F. (-268° C. to 482° C.). The company says the insulation consists entirely of glass with millions of completely sealed glass cells, each an insulating space, making it impermeable to water in liquid or vapor forms.

It is manufactured from soda (Na₂O), lime (CaO), and alumina (Al₂O₃), with silica (SiO₂) being the major constituent. Rigel Shipping says it is the inert nature of silica which provides cellular glass with its chemical durability.

Flammability is another concern for the shipping company, given its petroleum-product cargoes. Any insulation surrounding the thermal-oil lines would have to be nonflammable and noncombustible. And while some insulations are themselves noncombustible, says the company, such as mineral wool, fiber glass, and calcium silicates, these can and do absorb or "wick" combustible liquids. Consequently, they can contribute to spreading fire.

Foamglas Super K insulation is nonflammable and noncombustible; because of its impermeability, it cannot absorb or transport combustible liquids.

Before installing the insulation on all three vessels, Rigel Shipping installed it and spent a year (beginning September 1996) observing it aboard the Diamond Star. Prefabricated in 2-ft, 0.5-lb sections, 2-in. thick, Foamglas Super K insulation was applied to the newly installed thermal-oil pipeline. The insulation half rounds were butted together and covered with stainless steel jacketing (Fig. 2).

During the following year and subsequent Rigel Shipping inspections, the insulation proved impervious to moisture, nonflammable, lightweight, and durable, says the company.

It subsequently installed the insulation aboard its other vessels by September 1998. The thermal oil lines are operating at optimum efficiency and no problems have been detected, according to Rigel Shipping.

Since the company's vessels spend about 75% of their time at sea, with the remaining 25% in port either loading or unloading cargo, there's little time for maintenance or repair. Since overhauling the thermal-oil pipelines and replacing the insulation, Rigel Shipping anticipates the system will last for the rest of the ships' operational lives-a minimum of 15 years.