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S-TEN™

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

Application Examples for S-TEN

Table 1.7 Examples of Applications of S-TEN
Equipment Practical application examples Precautions in use
Application Grade Approximate plate thickness (mm)
S-TEN 1 S-TEN 2
Dry-type electrostatic precipitator Casing, duct, collecting electrode ○ ○ 1.2～8 The temperature of casings and ducts is 20～70℃ lower than that of flue gas, depending on the heat insulation conditions. It is estimated that the temperature of the collecting electrode and the gas is the same. In cases when dust accumulates, the absorbed H2SO4 is difficult to evaporate and leads to cases of more than expected corrosion. As a result, it is necessary to prevent dust accumulation.
Wet-type electrostatic precipitator Casing, duct, collecting electrode ○ ○ 3.2～12 In cases when the flow of scrubber water is constant against a wall surface, the corrosion mass increases (by 0.1 mm/yr on one side). Further, in cases when the scrubber water in such a situation has a low pH value, the corrosion mass will increase abruptly, thereby making it necessary to avoid the use of S-TEN.
Gas cooler Casing, duct ○ ○ 4.5～9 The temperature of casings and ducts is 20～70℃ lower than that of flue gas, depending on the heat insulation conditions. The mist droplet becomes large due to the deterioration of nozzle holes and does not evaporate to reach the casing, under which there are cases when unexpected corrosion occurs, and thus it is necessary to control the deterioration of nozzle holes.
Ash discharge blade - ○ 12～20 S-TEN 2 is most suitable for use as the material for the blades that discharge the ash accumulated in the bottom section of gas cooler. The stress-induced corrosion cracking attributable to the chlorides contained in the ash can be prevented from occurring.
Air
preheater		 Ljungströmtype basket case, element ○ ○ 0.6～6 Because of repeated fluctuations in wall surface temperature, dew-point corrosion from high to low temperatures occurs repeatedly, and the application advantage of S-TEN is exhibited to the high degree.
Tube ○ - 0.6～3.5 The tubes are constantly in the dew-point state, and accordingly, S-TEN is highly effective. S-TEN 1 tube is most suitable for such application.
Flue Duct, expansion ○ ○ 4.5～9 S-TEN of the no coating specifications or the acid resistantcoating specifications is suitable. When the temperature of the flue gas itself drops below the dew point, drainage accumulates in the flue bottom, frequently causing unexpectedly severe corrosion, and thus it is recommended to provide appropriate measures to carry out sufficient drainage and to prevent lowering of steel plate temperatures by means of external heat insulation.
Stack Internal cylinder ○ - 6～12
Flue-gas desulfurizer Flue-gas cylinder, after-burner duct ○ ○ 3.2～6 In the ducts leading to and from gas coolers and absorption towers, low pH solutions occasionally adhere to wall surfaces due to sulfuric acid mist, and therefore it is necessary to fully investigate drainage conditions.
Hydrochloric acid pickling tank Tank ○ - 9～20 The use for hydrochloric acid pickling tank in coating is suitable. S-TEN tanks have a high scratch resistance during use, and these tanks after use can be treated as the general recyclable steel material.

Precaution in the Use of S-TEN

  • 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.
  • 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.
  • 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.
  • 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.

Fig. 1.10 Corrosion behaviors of S-TEN in non-equilibrium regions

Table 1.8 Results of corrosion tests in the weakly acidic area (pH2 to 4)
Grade Corrosion rate (mg/cm2/hrs) Testing conditions
pH2 pH3 pH4
S-TEN 1 1.6 2.0 0.36 Test temperature: 30℃
Relative speed of specimen
and solution: 1.8 m/sec
Test time: 72 hrs
S-TEN 2 2.8 2.2 0.38
Mild Steel 8.2 2.5 0.36
SUS 304 ＜ 0.001 ＜ 0.001 ＜ 0.001
SUS 316 ＜ 0.001 ＜ 0.001 ＜ 0.001
SUS 410 0.51 ＜ 0.001 ＜ 0.001
SUS 430 0.001 ＜ 0.001 ＜ 0.001

Application Examples

Kashima Kyodo Electric Power

Catalogs

Sulfuric Acid and Hydrochloric Acid Dew-point Corrosion-resistant Steel S-TEN™ (1.74MB)PDFファイル

  • 1. Characteristics of S-TEN
    • Sulfuric Acid and Hydrochloric Acid Dew-point Corrosion
    • Advantages of S-TEN
    • Examinations in Applying S-TEN
    • Application Examples for S-TEN
    • Precautions in the Use of S-TEN
  • 2. Specifications and Available Sizes of S-TEN
    • Specifications of S-TEN
    • Available Sizes for S-TEN
  • 3. Characteristic Properties of S-TEN (Examples)
    • Chemical Composition and Mechanical Properties
    • High-Temperature Characteristics
    • Physical Properties
    • Corrosion Resistance
  • 4. Welding of S-TEN
    • Welding Materials
    • Welding Characteristics
    • Sulfuric Acid and Hydrochloric Acid Resistance of Welded Joints
    • Galvanic Corrosion in Corrosive Atmosphere
    • Property Qualification Test Results
  • 5. Application Examples
  • 6. Reference
    • Unit Conversion Table
    • Unit Conversion Charts

NIPPON STEEL’s Steel Products for Thermal Power Generation (4.30MB)PDFファイル

  • Proposing NIPPON STEEL's eco-friendly steel products for power plants
  • S-TENTM
  • BT-HT
  • CORSPACETM
  • ABREXTM
  • TITANIUM
  • NSHYPER BEAMTM
  • Hat-shaped Steel Sheet Pile / Hat-type and H-shape Combined High Stiffness Steel Sheet Pile

Corrosion-resistant Steel Plates (1.98MB)PDFファイル

Steel Plates (1.55MB)PDFファイル

  • Features
  • Available Grades
  • Authorized Steel Grades by Product Type
  • Manufacturing Process and Quality Control Points
  • Thermo-Mechanical Control Process (TMCP)
  • 400 N/mm2-class Tensile Strength Steel Plates (As-rolled) Available Sizes
  • 490 N/mm2-class Tensile Strength Steel Plates (As-rolled) Available Sizes
  • 490 N/mm2-class Tensile Strength Steel Plates (TMCP: Thermo-Mechanical Control Process) Available Sizes
  • Weldable High-tensile Strength Steel Plates: WEL-TENTM Series
  • Abrasion-resistant Steel Plates: ABREXTM Series
  • Abrasion-resistant Steel Plates for Low Temperatures: ABREXTM LT Series
  • Low-temperature Steel Plates: N-TUFTM Series
  • Sulfuric Acid-resisting Steel Plates: S-TENTM Series
  • Ni-Added Weathering Steel Plates: NAW-TENTM Series
  • Highly Corrosion-resisting Steel Plates: COR-TENTM Series
  • Corrosion-resistant Steel Plates for Export: COR-TENTM
  • High Tensile Steel Plates for Building Structures: BT–HT Series
  • Steel Plates for Elasto-plastic Hysteretic-type Dampers for Building Structures: BT-LYPTM
  • Electromagnetic Mild Steel Plates: NS–MIPTM
  • Information Required for Orders
  • Examples of Marking
  • Conclusions
  • Reference for Use of Steel Plates
  • Reference Tables of Standards
  • NIPPON STEEL Specifications Table of Correlations between Old and New Specifications

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