Recently, environmental issues are becoming pressing concerns. In parallel with this, construction of tall smokestacks, air preheaters, electrostatic precipitators and flue-gas desulfurizers and other treatment equipment has shown great strides.

Meanwhile, the mainstay industrial fuel has shifted from conventional coal to heavy oil, which poses a large problem of corrosion at the low-temperature section of flue-gas treatment equipment (in particular, air preheaters, flues and smokestacks) due to sulfur oxides.

The low-temperature section corrosion is the corrosion caused by high-temperature, highly-concentrated sulfuric acid, called sulfuric acid dew-point corrosion. This kind of corrosion differs from general atmospheric corrosion and causes heavy corrosion of not only ordinary steel but even stainless steel.
Further, because of the remarkable technological developments recently seen in dioxin countermeasures, flue-gas temperatures are increasingly being reduced from previous levels.

In conventional facilities where, formerly, only sulfuric acid dew-point corrosion occurred, there are now cases of hydrochloric acid dew-point corrosion that is caused by lower flue-gas temperatures resulting from remodeling with countermeasures against dioxins.

Developed to solve these problems is S-TEN—steel for welded structures, highly resistant to sulfuric acid and hydrochloric acid dew-point corrosion.
S-TEN 1 has effective resistance to both sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion, while S-TEN 2 is effectively resistant to sulfuric acid dew point corrosion.

Features

S-TEN is a sulfuric acid and hydrochloric acid dew-point corrosion-resistant steel developed by NIPPON STEEL using proprietary technology.

• S-TEN exhibits the best resistance to sulfuric acid and hydrochloric acid dew-point corrosion found in the flue-gas treatment equipment used with coal-fired boilers, waste incineration plants, etc. (This steel has the finest application record in the field of thermal power generation and waste incineration plants, according to surveys conducted by NIPPON STEEL)
• S-TEN was awarded the Ichimura Industrial Award Achivement Award in 2007

S-TEN has strength, workability and weldability that are comparable to ordinary steel.

S-TEN is more economical than stainless steel.

S-TEN offers a rich product line ranging from hot-rolled sheets (plates), cold-rolled sheets and pipe and tubes to welding materials.

• Hot-rolled sheets (plates) conform to JIS G 3106 SM400A (S-TEN 1) and SM490A (S-TEN 2).

S-TEN products are easily available because they are constantly stocked by retailer

Precaution in the Use of S-TEN

1. S-TEN are a group of low-alloy corrosion-resistant steels. It should be noted that despite dew point corrosion being inhibited in them, there still occurs rust formation and progress of corrosion also.
2. S-TEN, as shown in Fig. 1.6, are effective in inhibiting sulfuric acid dew point corrosion, as compared with other steel grades, but, as can beseen from their performance at 60°C and 70°C in this figure, there are temperature regions in which steels’ absolute corrosion weight losses become greater than those in the other temperature regions.
3. Careful note must be taken of the fact that S-TEN also tend to be more greatly susceptible to high-temperature corrosion and low-concentration sulfuric acid corrosion, than to corrosion occurring in the gas-liquid equilibrium state, as shown in Fig. 1.10.
4. Results of the corrosion test made at very thin concentrations of pH2 to 4 of sulfuric acid are shown in Table 1.8. As against corrosion by such weakly acidic or neutral liquid, stainless steels are most resistant, with very little corrosion weight loss. At concentrations of pH3 and over, there is no significant difference between ordinary steels and S-TEN.