Anwendungen im Bereich Korrosion

Corrosion-resistant Materials

The right selection of material makes the difference

Stainless steel is needed for numerous applications and industries. This material is used for a huge variety of purposes in essential sectors such as raw material extraction, pharmaceutical and chemical industries, plant construction, oil & gas, offshore applications etc. Mankenberg’s product range of flexible standard valves or project-related special valves is correspondingly broad.

 

The operating conditions at the customer’s site sometimes require ultraclean surfaces of the valves whilst other valves must be capable of sustaining the flow of dirty or highly corrosive media. Hence, the optimum solution is selected in close consultation with our engineers, technicians and sales staff. A particular challenge is to select the suitable material for applications in chemical-technical processes, in which caustic and / or corrosive fluids are used.

 

The same applies to the maritime domain or saline liquids, for which in general sea water-resistant material is needed. It requires special diligence and clarification of all the technical and chemical details in order to properly assess the loading conditions of the material and the interaction between the medium and the environmental conditions.

 

Stainless steels, i. e. corrosion-resistant steels, become resistant to corrosion because a so-called passive layer forms on the surface. Such layer consists of chromium-rich metallic oxide or metallic oxide hydrate preventing the direct contact of the metal with the corroding medium. Even in the event of small lesions, a new layer builds up independently at the relevant area. If this is not the case, for example due to a lack of oxygen, either pitting corrosion (1) or crevice corrosion (2) may occur.

 

Stainless steels have a percentage by mass of the element chromium of not less than 12 % and of the element carbon that should not exceed 0.12 %. Hence, the percentage of the alloying element chromium is decisive for the corrosion resistance of stainless steel. In case the steel contains further alloying elements such as molybdenum or the like, the material becomes more resistant also to highly aggressive operating conditions.

Types of Corrosion

Allgemeine Korrosion  

General Corrosion

» The passive layer is completely destroyed
» This type of corrosion depends on the consistency of the fluid
» Can be avoided by optimally selecting the material with respect     to the medium
 
Lochfraßkorrosion  

Pitting Corrosion

»

Can be avoided by selecting molybdenum-containing steel types

 
Spaltkorrosion  

Crevice Corrosion

»

Occurs in a design-related enclosed hollow space of the equipment and in a chloride-containing environment

» Can be prevented through avoiding enclosed hollow spaces already during the design phase
 
Korrosion durch Verunreinigung  

Corrosion by Contamination

»

Is caused by ferrous deposits and brings about a contamination

 
Interkristalline Korrosion  

Intergranular Corrosion

» Diffuses from the grain boundaries in heat-sensitized areas
» The chromium degrades and impairs the passivating effects
»

Can be avoided by selecting low-carbon steel types

 
Spannungsrißkorrosion  

Stress Corrosion Cracking

»

Occurs in a chloride-containing environment, when the equipment is exposed to high stress, for example

»

Transcrystalline or intergranular crack path at sensitized microstructures

»

Can be avoided by selecting a suitable stainless steel

Used corrosion-resistant Materials

Material No. Norm

Major Alloying Element -%

Pitting Index
(PREN)
Standard DIN EN ASTM Cr Ni Mo
Stainless Steel 1.4404 X2CrNiMo17-12-2 316L 16,5-18,5 10,0-13,0 2,0-2,5 23,0 - 28,0
  1.4571 X6CrNiMoTi17-12-2 316Ti 16,5-18,5 10,5-13,5 2,0-2,5 25,0
Duplex 1.4462 X2CrNiMoN22-5-3 A182F51 21,0-23,0 4,5-6,5 2,5-3,5 30,0 - 38,0
  1.4539 X2NiCrMoCu25-20-5 N08904 19,0-21,0 24,0-26,0 4,0-5,0 34,0 - 40,0
Super Duplex 1.4410 X2CrNiMo25-7-4 S32750 24,0-26,0 6,0-8,0 3,0-4,5 35,0 - 42,0
  1.4501 X2CrNiMoCuWN25-7-4 S32760 24,0-26,0 6,0-8,0 3,0-4,0 37,0 - 44,0
Cronifer 1925hMo 1.4529 X1NiCrMoCu25-20-7 N08926 19,0-21,0 24,0-26,0 6,0-7,0 41,0 - 48,0
245 SMO® 1.4547 X1CrNiMoCuN20-18-7 S31254 19,5-20,5 17,5-18,5 6,0-7,0 42,0 - 48,0
Hastelloy® C-4 2.4610 NiMo16Cr15Fe6W4 N06455 14,5-17,5 66,0 14,0-17,0  
Titanium 3.703   R50400        

The higher the PREN (pitting resistance equivalent), the more resistant to pitting and crevice corrosion | alloys with a PREN of > 33 are classified as sea water resistant | Hastelloy® C-4 and Titanium are classified as being highly resistant to sea water | PREN of stainless steels = % Cr + 3.3*% Mo + 16*% N | a higher PREN is required for an increasing salt content and/or rising temperature

References

» Alstrom » Evonik » MAN
» BHP Billiton » Exxon Mobile » Procter & Gamble
» Dräger Safety » Gaz de France » Shell
» DSM » General Electric » Total
» E.On » Lanxess » Voith Paper
 

Weiterführende Informationen

Applications

Typical Products

 
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