How does brass corrode?

Here you get to the tabular overview.

Dezincification

CW626N | CuZn33Pb1,5AlAs dezincification test
In the dezincification test according to ISO 6509, the virtually beta phase-free alloy shows, in addition to low surface corrosion, parts of intergranular dezincification.
Dezincification
the beta phase of an alpha / beta brass. The Zn-rich beta phase is attacked here. What remains is a "copper sponge".
Dezincification in a siphon made of CW506L | CuZn33
The piece of pipe sat horizontally under a wash basin and was replaced after about 25 years due to a leak. The brass pipe crumbled because, due to massive dezincification in many places, the entire wall thickness consisted only of copper sponge and corrosion product.
During dezincification, the brass (yellow) dissolves, the zinc corrodes (blue-gray), the copper is excreted as pure, but now spongy metal (reddish). The brass here has a pure alpha structure, the surface is nickel-plated.

 

Erosion corrosion

Erosion corrosion on the heating pipe
The damage mechanism leading to leakage is erosion corrosion caused by solid particles in the (warm) water. Preferably in the area of ​​deflections or changes in cross-section, these particles “sand” on a microscopic level along the pipe wall and finally open into a hole-shaped wall breakthrough (pitting corrosion type II).

 

Surface corrosion

Cold water pipe
Here a galvanized steel pipe was accidentally installed in a stainless steel cold water pipe system. The damage was not long in coming.

Corroded soft solder in hot water pipe
A solder joint in a hot water pipe fell apart after the tin solder corroded. Only the noble, two-layer Cu-Sn compound layer (Cu6Sn5) on the copper pipe (Fig. 2), the grain structure of which appears in the SEM as a freely solidified surface (Fig. 3), has remained. Pictures 4-6 show the already half-corroded neighboring solder joint in longitudinal section.
Surface and depression corrosion in a water pipe
A decades-old water pipe made of hot-dip galvanized structural steel is heavily corroded on the inside, with numerous wall breakthroughs. The zinc layer on the inside has long been depleted. Remnants of the zinc layer have been preserved on the outside, although the surface is slightly corroded and already full of cracks. On the outside is the pure zinc layer (light), underneath the intermetallic iron-zinc compound layer (brownish with a barely recognizable columnar structure).

 

Liquid metal induced stress corrosion cracking

Liquid metal induced stress corrosion cracking
In the present case, it is a hot-dip galvanized screw of a wind turbine. With the help of the backscatter contrast and the EDX analysis, concentrated elements of Sn and Pb could be detected in cracks under the zinc layer. Liquid metal-induced stress corrosion cracking is the term used to describe solder brittleness which, in the presence of high mechanical and / or thermal loads in a component, leads to embrittlement through contact with a liquid metal melt (e.g. during galvanizing). This loss of ductility either leads to smaller cracks in the base material, which are generally covered by the metallic coating, or directly to large, macroscopically visible cracks in the component.
Solder fragility at 1.0038 with CuAlNi2 solder
In this special form of stress corrosion cracking, the liquid copper solder represents the corrosion medium. The copper diffuses into the structural steel along the tensile stressed grain boundaries. As a result, intergranular cracks form in the base material. In the cracks is the reddish color
the causer can be seen very clearly.

 

Intergranular corrosion (IC)

1.4828 | X15CrNiSi20-12
This heat-resistant steel may contain a maximum of 0.20% carbon. An assembly of sheet metal and bar material was welded; the carbon contents differed significantly, but were all within the specification. The bar material has a higher carbon content of 0.13%. In the HAZ, this has led to finely dispersed carbide precipitations along the boundary. For the formation of carbide, Cr has diffused from the immediate vicinity and is present here locally <13%, which has led to a strong corrosive attack. After welding, the assembly was pickled a little longer than usual; you could also say forgot for 4 hours. The intergranular corrosion attack resulted in a 1/3 reduction in the wall thickness. The sheet material with only 0.06% C, on the other hand, shows only a slight corrosion attack. The component was discarded. In the future, the customer will forego pickling altogether and have switched to brushing the weld seams.

 

High temperature corrosion

1.4460 | X3CrNiMo27-5-2 High temperature corrosion on a furnace door
Scale formation and massive carburization.

 

Cavitation corrosion

Cavitation corrosion on the condensate collection pipe
The following images show cavitation damage to a condensate collecting pipe from a steam generator.

 

Pitting corrosion

Pitting corrosion on 1.4305 after 24 hours of use in "stale water"
Cause of damage and corrosion mechanism:
The manganese sulphides typical for this material interfere with the local passivation of the surface. There is also local mechanical damage in the area of ​​the corrosion damage. In addition to MnS, mechanical damage also damages the passive layer that protects against corrosion attack. By means of EDX analysis, a concentration of the element chlorine could be detected, which caused pitting corrosion. The resistance to chlorine is max.200mg / L at room temperature. A further complicating factor is that little oxygen gets into the hole due to the resulting small hole diameter, which prevents repassivation. Since the oxygen content outside the hole is much greater than in the hole, a concentration element is also formed, which accelerates the pitting corrosion.
Pitting corrosion attack
a brushed aluminum surface. The cause of corrosion are metallic foreign particles that have formed a galvanic element. A CrNi steel was apparently previously brushed with the same brush tool.

 

Well corrosion

1.4509 | X2CrTiNb18 Well / crevice corrosion
This corrosion-resistant ferritic Cr-steel suffered well or local surface corrosion, triggered by high Cl and S contents in a gap.
1.4521 | X2CrMoTi18-2 Well corrosion
Crevice corrosion took place on this ferritic chrome steel in the form of a trough-shaped corrosion attack on an elbow crimped connection of a drinking water pipe.
High proportions of chlorine could be detected in the corrosion products, which have concentrated here.

 

Layer corrosion

Layer corrosion on EN AW-7075 T6 | AlZn5.5MgCu
Layer corrosion is a layer-like, selective corrosion, which here is intergranular and, in sensitive areas, preferably in planes parallel to the rolling plane. The extensive peeling is caused by the voluminous corrosion products that are formed.

 

Stress corrosion cracking SpRk

 

Spongiosis

Corrosion cancellous lamellar cast iron
Spongiosis (spongy dissolution) is a form of selective corrosion of cast iron, in which the corrosive attack progresses along the graphite-matrix interfaces and dissolves the iron matrix. With long graphite lamellas, as in this pearlitic lamellar gray cast iron, a deep penetration of the corrosion is possible. The graphite is retained and holds the corrosion product together. The original shape of the casting is retained, but the black "iron sponge" (mainly FeOOH) no longer has any strength.
Corrosion Spongiosis of degenerate nodular cast iron
Spongiosis (spongy dissolution) is a form of selective corrosion of cast iron, in which the corrosive attack progresses along the graphite-matrix interfaces and dissolves the iron matrix. In this example, the corrosion followed the degenerate graphite spheres (chunky graphite) in a ferritic matrix.

 

 

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