Stress Corrosion Cracking: Understanding Causes, Effects, and Prevention
Stress Corrosion Cracking occurs when metals are exposed to tensile stresses and corrosive mediums at the same time. Learn how this applies to brass products.
Last Updated: Sep 2, 2024
Stress Corrosion Cracking (SCC) can pose a risk to metals, particularly brass used in compression fittings.
Type A Compression Fittings
Flowflex Compression Fittings are the perfect solution for your plumbing needs, offering unparalleled reliability and ease of installation. Crafted from high-quality materials, these fittings ensure a secure and leak-free connection, making them ideal for both residential and commercial applications. Our compression fittings are designed and manufactured to BS EN 1254 standard, providing you with peace of mind and long-lasting results.
Stress Corrosion Cracking (SCC) occasionally occurs in metals when they are exposed to both a corrosive medium and tensile stresses. For brass used in compression fittings, SCC is almost always introduced during installation due to over-tightening and contamination by a stress-cracking agent.
What Causes Stress Corrosion Cracking
SCC occurs when the following conditions are met simultaneously:
A Susceptible Material: In this context, brass.
Contaminated Environment: In this case moisture, ammonia or ammoniacal compounds,
Tensile stress: Application of tensile stress on the material.
SCC In Brass Compression Fittings
The most common cause of SCC in brass compression fittings is exposure to ammonia or ammoniacal compounds. These substances are found in various sources, including cleaning fluids, refrigeration gases, sewage waste products, building materials, insulating materials (especially foams), and flame and smoke retardant treatments.
Moisture plays a significant role in the SCC process. It acts as a catalyst by allowing corrosive substances to accumulate and become more concentrated. This is particularly problematic in chilled water installations, where insulating materials can retain condensed moisture and keep it in close contact with the surface.
How Can I avoid Stress Corrosion Cracking
Avoiding SCC is straightforward when following good installation practices and the manufacturer’s instructions. Alternatively, consider using fittings made of copper or bronze for your application.
For Flowflex Brass Compression Fittings, alongside our installation instructions, the following advice is crucial:
Proper Thread Tightening: When tightening male taper threads into female parallel threads, do not over tighten. Use PTFE tape or an approved sealant to ensure a secure fit.
Use the Correct Tools: Use a flat-faced, high-quality spanner that matches the size of the nut.
Lubrication for Larger Fittings: For compression fittings larger than 28mm, apply light oil to the threads. This reduces the force needed to tighten the fitting and decreases stress.
Avoid Stress-Cracking Agents: Ensure no stress-cracking agents are present near the installation. If uncertain, consider using a different jointing method, such as Flowflex Copper Capillary fittings or Flowflex Copper Press.
Protection in Aggressive Environments: In environments conducive to SCC, you should protect Flowflex Brass Compression Fittings from aggressive moisture by wrapping the fittings with an appropriate impervious tape.
Overall, installers should ensure that all Brass Compression connections are not over tightened, and that the environment into which they are installed is not conducive to the cause of Stress Corrosion Cracking as outlined above.
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