4.4.7. Stress Corrosion Cracking

Reference: Abbott, Richard. Analysis and Design of Composite and Metallic Flight Vehicle Structures 3 Edition, 2019

Ref:  (MSFC-SPEC-522B, 1987), (ECSS-Q-ST-70-36C, 2009)

Stress corrosion may be defined as the combined action of sustained tensile stress and corrosion to cause premature failure of, materials.Certain materials are more susceptible to stress corrosion cracking (SCC) than others. If a susceptible material is placed in service in a corrosive environment under tension of sufficient magnitude, and the duration of service is sufficient to permit the initiation and growth of cracks, failure occurs at a stress lower than that which the material is normally be expected to withstand. The corrosive environment need not be severe in terms of general corrosive attack.

Service failures due to stress‐corrosion are frequently encountered in cases where the surfaces of the failed parts are not visibly corroded in a general sense.

Stresses are additive and threshold stresses for susceptibility are often low. There have been a number of stress‐corrosion failures for which design stresses were intermittent and of short duration, and only of minor significance in contributing to failure. Stress‐corrosion cracking in those cases occurred because of a combination of residual and assembly stresses not anticipated in design.

Resistance to stress corrosion cracking of metal alloys mainly depends on Grain Orientation (Reference Section 4.2.2) and Material Susceptibility to Stress Corrosion Cracking (Section 4.4.7.1 below).

Protective coatings such as electroplate, anodize or chemical conversion coatings do not change the stress corrosion rating of alloys to which they are applied.

Surface treatments such as carburizing or nitriding may adversely affect the stress corrosion rating of materials to which they are applied.

4.4.7.1. Common Situations which result in Stress Corrosion Problems

Figure 4.4.7‑1: Assembly Stress Resulting from Mismatch (MSFC-SPEC-522B, 1987)
Figure 4.4.7‑2: Assembly Stress Resulting from Excessive Clearance (MSFC-SPEC-522B, 1987)
Figure 4.4.7‑3: Assembly Stress in Forging with Excessive Clearance (MSFC-SPEC-522B, 1987)

4.4.7.2. Alloys with High Resistance to Stress Corrosion Cracking

Table 4.4.7‑1 Steel Alloys with High Resistance to Stress-Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑2 Nickel Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑3 Aluminum Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑4 Copper Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)

4.4.7.3. Alloys with Low Resistance to Stress Corrosion Cracking

Table 4.4.7‑5 Steel Alloys with Low Resistance to Stress-Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑6 Aluminum Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑7 Copper Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑8 Magnesium Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)

4.4.7. Stress Corrosion Cracking

Reference: Abbott, Richard. Analysis and Design of Composite and Metallic Flight Vehicle Structures 3 Edition, 2019

Ref:  (MSFC-SPEC-522B, 1987), (ECSS-Q-ST-70-36C, 2009)

Stress corrosion may be defined as the combined action of sustained tensile stress and corrosion to cause premature failure of, materials.Certain materials are more susceptible to stress corrosion cracking (SCC) than others. If a susceptible material is placed in service in a corrosive environment under tension of sufficient magnitude, and the duration of service is sufficient to permit the initiation and growth of cracks, failure occurs at a stress lower than that which the material is normally be expected to withstand. The corrosive environment need not be severe in terms of general corrosive attack.

Service failures due to stress‐corrosion are frequently encountered in cases where the surfaces of the failed parts are not visibly corroded in a general sense.

Stresses are additive and threshold stresses for susceptibility are often low. There have been a number of stress‐corrosion failures for which design stresses were intermittent and of short duration, and only of minor significance in contributing to failure. Stress‐corrosion cracking in those cases occurred because of a combination of residual and assembly stresses not anticipated in design.

Resistance to stress corrosion cracking of metal alloys mainly depends on Grain Orientation (Reference Section 4.2.2) and Material Susceptibility to Stress Corrosion Cracking (Section 4.4.7.1 below).

Protective coatings such as electroplate, anodize or chemical conversion coatings do not change the stress corrosion rating of alloys to which they are applied.

Surface treatments such as carburizing or nitriding may adversely affect the stress corrosion rating of materials to which they are applied.

4.4.7.1. Common Situations which result in Stress Corrosion Problems

Figure 4.4.7‑1: Assembly Stress Resulting from Mismatch (MSFC-SPEC-522B, 1987)
Figure 4.4.7‑2: Assembly Stress Resulting from Excessive Clearance (MSFC-SPEC-522B, 1987)
Figure 4.4.7‑3: Assembly Stress in Forging with Excessive Clearance (MSFC-SPEC-522B, 1987)

4.4.7.2. Alloys with High Resistance to Stress Corrosion Cracking

Table 4.4.7‑1 Steel Alloys with High Resistance to Stress-Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑2 Nickel Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑3 Aluminum Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑4 Copper Alloys with High Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)

4.4.7.3. Alloys with Low Resistance to Stress Corrosion Cracking

Table 4.4.7‑5 Steel Alloys with Low Resistance to Stress-Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑6 Aluminum Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑7 Copper Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)
Table 4.4.7‑8 Magnesium Alloys with Low Resistance to Stress Corrosion Cracking (ECSS-Q-ST-70-36C, 2009)