Applications of stainless steel pipes in shipbuilding and marine engineering

Applications of Stainless Steel Pipes in Marine Engineering

Stainless steel pipes are widely used in marine engineering. The two major systems in shipbuilding and offshore engineering generally require three types of steel pipes: pipes in conventional systems, pipes used in structures, and pipes for special purposes.

Stainless Steel Pipes in Conventional Systems

Different ships and offshore engineering projects have both conventional and specialized systems.

The service life of a ship is generally 20 years. There are many conventional systems, mainly including bilge water, ballast, drainage, sewage, air, measurement, injection, domestic water, fire fighting, cargo oil, tank cleaning, ventilation, inert gas, heating, tank washing, foam fire extinguishing, sprinkler systems, vapor recovery, liquid level remote sensing, and valve remote control systems. Special vessels also include dedicated systems for transporting liquefied petroleum gas (LPG), liquefied natural gas (LNG), etc. Offshore engineering projects have a service life of 30 years or even longer. In addition to conventional systems, offshore engineering projects also include special drilling and production equipment systems, crude oil/LPG/LNG processing systems, special mooring systems, flare systems, and so on.

It has been estimated that the annual consumption of pipes in the shipbuilding industry reaches 4.5 million tons, approximately 440,000 pipes, with standards such as GB, VB, and CB.  70% of these stainless steel pipes are connected by flanges. A single 300,000-ton supertanker can use tens of kilometers of stainless steel pipes, with a total weight of about 1500 tons. Of course, this is still limited compared to the 40,000 tons of steel used in the hull structure. However, considering that multiple ships of the same type are built, and there are many other types of ships, the cumulative consumption is considerable. A 300,000-ton FPSO (Floating Production, Storage and Offloading) vessel uses more than 30,000 stainless steel pipes, with a total length exceeding 90 kilometers, which is 2-3 times that of a vessel of the same tonnage. Therefore, the shipbuilding industry has become a major user of stainless steel pipes.

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Stainless Steel Pipes in Structures

In addition to the conventional and specialized systems mentioned above, many structures in offshore engineering utilize stainless steel pipes extensively, such as jacket structures, underwater steel piles, riser mooring supports, helicopter platforms, and flare towers. These stainless steel pipes come in a wide range of specifications and high-quality materials, including pipes of the same and different diameters, varying wall thicknesses, and numerous K and T-type pipe joints. For example, jacket structures, steel piles, and riser casings often use large-diameter stainless steel pipes, which are generally fabricated by rolling steel plates. Their materials are E36-Z35, D36.Z35, E36, and D36. The standards for these stainless steel pipes are not B or CB, but primarily GB712-2000. The manufacturing of these stainless steel pipes follows the "Specification for the Manufacture of Structural Steel Pipes" SY/T10002-2000, formulated by the my country Petroleum Industry Standards Technical Committee (CPSC). Since there are no specialized companies in my country for this purpose, the construction units usually purchase steel plates and process them into the required shapes themselves.

Special Purpose Stainless Steel Pipes

Special purpose stainless steel pipes refer to special stainless steel pipes used in specific working environments and with specific working media. Subsea oil pipelines are typical examples of special stainless steel pipes, with a large demand and characteristics such as high strength, small tolerances, and good corrosion resistance.

The 321 stainless steel pipes manufactured by Hongdi are ideal for ship components:  321 stainless steel contains Ti as a stabilizing element, but it is also a heat-resistant steel, performing much better at high temperatures than 316L. 321 stainless steel has good corrosion resistance in organic and inorganic acids of different concentrations and temperatures, especially in oxidizing media, and is used to manufacture linings for acid-resistant containers and wear-resistant equipment, and for conveying pipelines. 321 stainless steel is a Ni-Cr-Ti type austenitic stainless steel, whose performance is very similar to 304, but the addition of titanium gives it better resistance to intergranular corrosion and higher temperature strength. The addition of titanium effectively controls the formation of chromium carbide. 321 stainless steel tubing exhibits excellent high-temperature stress rupture and creep resistance properties, with superior mechanical properties compared to 304 stainless steel.  It is suitable for welded components used at high temperatures. 321 stainless steel contains added titanium (Ti) to prevent intergranular corrosion in 304 steel. It is suitable for use at temperatures between 430℃ and 900℃.

Applications: Medical equipment, building materials, chemical industry, agriculture, ship components, nuclear energy industry, aircraft, exhaust pipes, boiler drums, automotive parts.