Chemical Tanker - Why Use Stainless Steel (from Shipyard Perspective)

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.

Source: Shipyard Ottokumpu

Why stainless, why duplex 2205 for chemical tankers
Stainless chemical tanker compartments
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.

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.