Chemical tankers are the multitasking force among the international cargo fleet. They are expected to alternate flexibly between cargoes as incompatible as inorganic acids and edible oils.

Today’s trends in chemical-tanker ownership and operation models further enhance needs to switch smoothly from one kind of cargo to another: shipowners can lease their tankers for up to five years, with little knowledge or control over the cargoes the tankers may carry.

Stainless steel is the unbeatable material for chemical-tanker compartments to make the switches easy and safe. Stainless can best withstand the test of abrasive and corrosive washing with high-pressure water jets and hot seawater between unloading and reloading, to avoid cross-contamination – the highly unwelcome incident where residues of the previous cargo are mixed with the next. Cross-contamination can be fought further by polishing the stainless surfaces to smooth 2.2 micron finish.

M/t Turchese of Finbeta SpA. Courtesy of same.

The polishing has so far been a laborious task done by hand at the shipyard. Outokumpu now puts this practice into history, with the company’s exceptional plate prefabrication and surface-treatment capabilities, first put to work on two 9400dwt full-stainless steel chemical tankers under construction for the Italian shipowner Finbeta SpA.

A full value-added package from Outokumpu with pre-polished plate

Important for Finbeta is, first, stainless steel for quality cargo shipment and, second, procuring the stainless materials from Outokumpu. The two companies’ cooperation in stainless chemical tankers goes back two decades. For their ongoing shipbuilding project, Finbeta made a thorough screening of shipyards to find one fully capable of stainless chemical tanker building, with the precondition to use Outokumpu’s stainless plate as prefabricated sections.

Prefabrication at Outokumpu’s plate operations produces tailor-made components, ready for assembly at the shipyard. It includes corrugation and welding of plate segments, welding preparation for the rest and, now for the first time by any stainless plate supplier, polishing of the surfaces to 2.20 micron finish, performed at the Outokumpu plate operations in Sweden. Outokumpu is the only stainless plate supplier to have this plate surface capability in house. Pre-polishing not only produces the desired smoothness but also a highly uniform outcome.

Outokumpu’s full package of prefabricated and pre-polished plate sections brings exceptional value added for chemical-tanker owners and builders. It considerably facilitates tanker building by allowing the customer to procure the entire package of stainless plate products and services from one house. Even the task of plate authorizing agents is all the more simplified with only one address to visit.

Why stainless, why duplex 2205 for chemical tankers

The chemical tanker emerged in the 1960s as chemicals trading was expanding rapidly throughout the world.

Chemical tankers differ from oil tankers in technical sophistication. With many separate compartments integrated into the hull, they are more robust, largely owing to the subdivision created by the bulkheads between cargo tanks. The cargoes are usually of high value (worth up to millions of dollars) and range from hazardous and noxious chemicals to liquids for human consumption.

Well over a thousand stainless steel chemical tankers sail the seas today, and one out of four new chemical tankers are stainless. Of all commercially transported chemicals, amounting to thousands, only about a dozen require some other material than stainless, while international regulations prescribe that a high number must be transported in stainless compartments.

Stainless chemical tanker compartments

A number of facts speak for stainless in chemical tankers. The efficient and fast washing between cargoes enabled by stainless compartments not only protects valuable cargoes the best against cross-contamination, stainless also ensures that the tanker (a multi-million dollar investment) can be quickly turned around at the dock, maximizing sea time. Less than ten percent of all stainless chemical tankers built since the 1960s have been scrapped, proving that they retain their value for decades. There is no need to make provisions for material loss over time.

While fairly high-alloyed grades of stainless are recommended for chemical tankers, to allow for the harshest chemicals, the trend in new tankers is increasingly towards grade 2205 (1.4462) duplex stainless steel (3.1% molybdenum for high corrosion resistance).

Duplex 2205 has been used in well over 200 tankers to date, and it is obvious that this grade will dominate in the future due to its many advantages. A major advantage with the duplex grade is its high strength, which enables considerable plate thickness reduction and, as a result, both materials savings and higher payloads.

Italian shipowners pioneered the use of duplex 2205 as early as the 1980s, attracted to the wide cargo list allowed by the grade. In the 15 years to follow, units that now are part of Outokumpu supplied for 73 of the 76 stainless chemical tankers built in Italy – amounting to 55,000 tons of plate, augmented by stainless piping.

More than half of the stainless steel chemical tankers in traffic today have been built with Outokumpu plate. Outokumpu continues to supply for chemical tankers worldwide.

Today, shipowners often maintain the design and engineering of chemical tankers in house, while shipbuilding takes place in other countries. In the case of the two new 9400dwt chemical tankers supplied for by Outokumpu, the Italian shipowner Finbeta SpA retains the decision on stainless steel grades, prefabrication and pre-polishing, contracting construction to a shipyard elsewhere.