What causes HDPE to crack?
Due to its high density, HDPE is a crystalline material and when a high tensile stress is applied the material will stretch and yield before ductile failure, but at low tensile stress, the material will fail suddenly with a smooth break typical of brittle failure. This is known as environmental stress cracking.
What causes stress corrosion cracking?
Stress corrosion cracking (SCC) is the cracking induced from the combined influence of tensile stress and a corrosive environment. The impact of SCC on a material usually falls between dry cracking and the fatigue threshold of that material.
Is HDPE brittle?
In HDPE pressure pipe applications, brittle failure is the most common mode of failure; it is characterized by the slow and steady growth of a crack that is initiated at a defect or stress concentration in the pipe.
What causes cracks in plastic?
When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. The polymer chains eventually creep toward the pull and deform. This stage is called creep. With force and time, crazing or stress cracking occurs.
What causes crazing in plastics?
Crazing develops when excessive tensile stress is applied to a polymer, leading to microvoid formation in a plane normal to the stress. The voids initiate at microscopic inhomogeneities in the polymer, and are stabilised by fibrils of plastically deformed polymer chains.
How can I improve my HDPE ESCR?
Vistamaxx™ performance polymers can be used to improve the Environmental Stress Crack Resistance (ESCR) of high density polyethylene (HDPE). Because parts made with Vistamaxx enhanced HDPE are tougher than those made with pure HDPE, they are less likely to fail through environmental stress cracking.
Is an effective inspection method to detect stress corrosion cracks?
The Phased Array UT is effective method to detect Stress Corrosion Cracking on heavy wall reactors compare to TOFD or any other conventional NDT techniques and however the challenges always remain on sizing and plotting the orientation.
How does stress affect corrosion?
It is found that stress can accelerate the corrosion process and contribute to intergranular corrosion and intergranular stress corrosion cracking of steel. Consequently, stress can expedite the reduction of mechanical properties of corroded steel, especially the ultimate strength and failure strain.
Does HDPE break easily?
HDPE is famous for being very rigid, but it’s not brittle. It won’t break when bent with two hands or the average tool – even if the Hulk were to give it a try.
What are the main causes of plastic shrinkage cracks?
simplistically, plastic shrinkage cracking occurs when the rate of evaporation of moisture from the surface exceeds the rate at which moisture is being supplied to it (via bleeding from the concrete). The concrete surface dries out and shrinks at a time at which it has little strength and hence it cracks.
What does ESCR stand for?
Acronym. Definition. ESCR. Economic, Social, and Cultural Rights.
How do you identify stress corrosion?
Detecting Stress Corrosion Cracking and HTHA with Ultrasonic Inspection
- Produce a scan of the inspection surface to provide high-resolution imaging.
- Focus beams to allow for identification of air bubbles and cracks as well as accurate positioning of these flaws.
Do shrinkage cracks need to be repaired?
Shrinkage cracks in a concrete slab or floor might need to be repaired to avoid water leakage from below or to stop radon gas entering the building.
What is stress cracking of HDPE?
Basic understanding of stress cracking in HDPE products Environment stress cracking of HDPE products is quite common because of its semi crystalline nature which gets attacked due to chemicals present in the environment. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging.
How to control stress corrosion cracking?
As one of the requirements for stress corrosion cracking is the presence of stress in the components, one method of control is to eliminate that stress, or at least reduce it below the threshold stress for SCC.
How do you detect stress corrosion cracking in pipes?
A close-up of the surface of a steel pipeline showing indications of stress corrosion cracking (two clusters of small black lines) revealed by magnetic particle inspection. Cracks which would normally have been invisible are detectable due to the magnetic particles clustering at the crack openings.
What grade of HDPE has the best crack resistance?
Switch to a more crack-resistant HDPE grade. A slightly less crystalline HDPE will have better crack resistance, and density is a direct measure of crystallinity. A HDPE grade of 0.95 density would perform better compared to the 0.054 density grade.