Zhejiang Guanyu Stainless Steel Tube Co., Ltd  
  Directory | Useful Tool | Sitemap | Contact US | Home

         

Stainless Steel

Passivation of Stainless Steel Tube






Stainless steel are designed to naturally self-passivate whenever a clean surface is exposed to an environment that can provide enough oxygen to form the chromium rich oxide surface layer, on which the corrosion resistance of these alloys depends. Naturally occurring conditions such air or aerated water will do this and so under many exposure conditions stainless steel will naturally self-passivate.

Principle of pickling and passivation of stainless steel

The corrosion resistance of stainless steel is mainly due to the fact that the surface is covered with an extremely thin (about 1nm) dense passivation film. This film isolates 1n corrosive media and is the basic barrier for stainless steel protection. Stainless steel passivation has dynamic characteristics and should not be regarded as a complete stop of corrosion, but rather forms a diffusion barrier that greatly reduces the anode reaction speed. Usually, membranes tend to be damaged in the presence of reducing agents (such as chloride ions), but can be maintained or repaired in the presence of oxidants (such as air).

Stainless steel workpieces will form an oxide film when placed in the air, but the protection of this film is not perfect enough. Usually, thorough cleaning, including alkali washing and pickling, and then passivation with oxidants are required to ensure the integrity and stability of the passivation film. One of the purposes of pickling is to create favorable conditions for passivation treatment and ensure the formation of a high-quality passivation film. Because an average of 10 μm thick layer on the surface of stainless steel is corroded through pickling, the chemical activity of the acid makes the dissolution rate of defective parts higher than other parts on the surface, so pickling can make the entire surface even and balanced, some of the original Hidden hazards that could easily cause corrosion are eliminated.

But more importantly, through pickling and passivation, iron and iron oxides are dissolved preferentially than chromium and chromium oxides, and the chromium-poor layer is removed, causing chromium to be enriched on the surface of stainless steel. This chromium-rich passivation film The potential can reach +1.0V (SCE), which is close to the potential of precious metals, improving the stability of anti-corrosion. Different passivation treatments will also affect the composition and structure of the film, thereby affecting the rust resistance. For example, through electrochemical modification treatment, the passivation film can have a multi-layer structure, forming CrO3 or Cr2O3 in the barrier layer, or forming a glassy state. The oxide film enables stainless steel to exert maximum corrosion resistance.

Pickling, passivation and removing iron contamination with nitric acid
Passivation treatments are sometimes specified, but it is important to consider whether this is strictly necessary or not. Stainless steel cannot be passivated unless the steel surface is clean and free from contamination and scale from welding operations.

Scale may need to be removed first by 'pickling' or mechanical abrasion and although the surface of freshly pickled stainless steel will normally be immediately passivated once the pickling acid has been washed off, it is important not to regard these two treatments as the same.

Pickling usually involves nitric acids / hydrofluoric acids mixtures, whereas, traditionally passivation has been done using only nitric acid. Nitric acid alone can be used to remove light surface iron contamination after which the acid facilitates the passivation of the cleaned steel surface.

Citric acid passivation as an alternative to nitric acid treatments

Citric acid treatments can also be considered as an alternative to nitric acid as both provide the oxidising conditions necessary for passivation. Citric acid is a less hazardous method and has environmental benefits in terms of 'NOx' fume emission and waste acid disposal. Solution strengths of 4-10% citric acid are specified for passivation treatments in ASTM A967.

Specifications for passivation treatments for stainless steel.

Traditionally the American standards have been used.

These include: -

ASTM A380 - Practice for Cleaning, Descaling and Passivating of Stainless Steel Parts, Equipment and Systems

ASTM A967 - Specification for Chemical Passivation Treatments for Stainless Steel Parts (based on US Defense Department standard QQ-P-35C)

In 1997 an alternative British Standard was published:

EN 2516 - Passivation of Corrosion Resisting Steels and Decontamination of Nickel Base Alloys




Metal Glossary | Metals Definitions | Heat Treatment of Metals | Passivation | Annealing | Quenching | Tempering | Heat Treatment of Steel | Heat Treating Definition | Heat Treating Stainless Steel | Technic of Metals Heat Treatment | Elements in Annealed State | Bright Anneaing | ASTM A380 | ASTM A967 | EN 2516 | 304 | 304L | 321 | 316L | 317L | 310S | 410 | 410S

Heat Transfer | Forms | Effects | Conduction | Convection | Radiation | Heat Exchanger


Словарь сокращений, используемых в нефтегазовой отрасли
  Stainless Steel Tubing, Nickel Alloy Tubing, Brass Alloy Tubing, Copper Nickel Pipe Material Grades


TubingChina.com All Rights Reserved

Directory | Standard | Heat | Heat Exchanger | Temperature | Pressure | Corrosion | Hardness | Surface | Properties | Select Stainless Steel | Contact US

Useful Tools:

Stainless Steel Weight Calculator
Metals Weight Calculator
Nickel Alloy Weight Calculator
Copper Brass Alloy Weight Calculator
Copper Brass Alloy Sheet Plate Weight Calculator
Sheet Plate Weight Calculator
Hardness Conversion Calculator
Hardness Conversion Chart
Rockwell Brinell Vickers Shore Hardness Conversion Chart
Conversion Calculator
Length Weight Temperature Volume Pressure Calculater
Pipe Working Pressure Calculator
Pressure Conversion Converter
Round Bar Size Calculator
Gauge Sizes
Sheet Metal Gauge
Pipe Schedule
Nominal Pipe Size
ANSI Pipe Chart
Inch to mm Chart
Stainless Steel Pipe Sizes
Stainless Steel Tubing Sizes Chart
Stainless Steel L H Grade
Stainless Steel Density
Conversion of Stainless Steel
Nickel Alloy Grades Comparison Material Grade Chart Carbon Steel
Structural Steel Comparison Chart



Main Products:

BA Tube | AP Tube
Condenser Tubes Tubing
Stainless Steel Reheater Tube Superheater Tubes
Stainless Steel U bend Tube
Nickel Alloy U bend Tubes
Copper Alloy U Bend Tubes
Heat Exchanger Tube
Super Duplex Pipe
Nickel Alloy Tube
Brass Alloy Tubing
Copper Nickel Alloys Tubes
Stainless Steel Hollow Tube
Stainless Steel Oval Tubing
Stainless Steel Square Tubing
Stainless Steel Rectangular Tubing
Stainless Steel Capillary Tube
Duplex Stainless Steel Pipe
Seamless Stainless Steel Tubing
Corrugated Stainless Steel Tubing
Stainless Steel Twisted Tube
Polishing Stainless Steel Tubing
Stainless Steel Aircraft Tube
Stainless Steel Hydraulic Tubing
Stainless Steel Instrumentation Tubing
Stainless Steel Angle Iron Bar
Stainless Steel Mechanical Tube
Bright Annealing Stainless Tube
Heat resistant Stainless Steel
Stainless Steel Welded Pipe
Extruded Serrated Finned Tubes Integral Finned Tubes / Extruded Aluminum Finned Tubes
Brass Alloys Copper Nickel Alloy Integral Low Finned Tubes
HFW High Frequency Welded Helical Spiral Serrated Finned Tubes
Corrosion Resistant Stainless Steel
Corrosion Resistance Stainless Steel

Stainless Steel Tubing Pipe

304 Stainless Steel Pipe
304L Stainless Steel Pipe
304H Stainless Steel Pipe
304/304L Stainless Steel Tubing
309S Stainless Steel Pipe
310S Stainless Steel Pipe
316L Stainless Steel Tubing
316Ti Stainless Steel Tube
317L Stainless Steel Pipe
321 321H Stainless Steel
347 347H Stainless Steel
904L N08094 Seamless Tubes
17-4 PH 630 UNS S17400 Stainless Steel
253MA S30815 Stainless Steel Tube
S31254 254 SMO Pipe
S31803 Stainless Steel
2205 Duplex Pipe Tubing
S32101 Stainless Steel
S32304 Stainless Steel
2507 Super Duplex Pipe
S32750 Super Duplex Pipe
S32760 Super Duplex Steel
1.4462 Stainless Steel Pipe
ASTM A213 | ASTM A269
ASTM A312 | ASTM A511
ASTM A789 | ASTM A790
ASTM B161 / ASME SB 161 | ASTM B111
EN 10216-5
ASTM A789 ASME SA 789 S31803 S32205 S32101 S32750 S32760 S32304 S31500 S31260 Seamless Tubes
EN 10216-5 1.4462 1.4362 1.4162 1.4410 1.4501 Seamless Tubes
Nickel Alloy Tubing:

UNS N08020 Alloy 20 Tubing
UNS N02200 Alloy 200 Tube
UNS N02201 Alloy 201 Pipe
UNS N04400 Monel 400 Tubing
N06600 Inconel 600 Tube
N06601 Inconel 601 Tubing
N06625 Inconel 625 Tubes
N08800 Incoloy 800 Tube
N08810 Incoloy 800H Tube
N08811 Incoloy 800HT Tubing
UNS N08825 Incoloy 825 Pipe
ASTM B622 N10276 C276 Tubing
ASTM B622 N06022 Hastelloy C-22 Alloy Tubes
C28000 Brass Seamless Tubes C44300 Brass Seamless Tubes
C68700 Brass Seamless Tubes
C70600 Copper Nickel Tubes
C71500 Copper Nickel Tubes
DIN 2391 Seamless Precision Steel Tubes
EN 10305-1 E215 E235 E355 Seamless Precision Steel Tube Tubing Tubes
DIN 2393 St28 St34.2 St37.2 St44.2 St52.3 Welded Precision Steel Tubes
EN 10305-2 E195 E235 E355 Welded Cold Drawn Precision Steel Tube