Dissimilar metal welds (DMWs) are commonly used when a high strength steel is overlaid with a corrosion resistant alloy (CRA) for petrochemical applications. There have been reported failures of these DMWs during subsea service while under cathodic protection (CP). These failures are caused by local hydrogen embrittlement of susceptible microstructures that form at the weld fusion boundary. Hydrogen-assisted cracking (HAC) occurs as a result of the local embrittlement and is influenced by base/filler metal combinations, and welding and post-weld heat treatment (PWHT) procedures. A delayed hydrogen cracking test was used to simulate tensile load and hydrogen charging on 8630-FM 625 weld. The failure of this sample was recorded using a high-speed camera to capture the crack initiation and propagation during failure. Fractography was performed using a scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS). The fracture surfaces, EDS measurement and video timestamps revealed brittle fracture nucleation in the planar growth and CGHAZ regions of the weld. The cracking continued to propagate through the same regions of the weld leading to final ductile failure (microvoid coalescence) in the cellular dendritic region of the weld.
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Stress-corrosion cracking of polypropylene in harsh oxidizing environments
Thermoplastic pipes are widely used in the semiconductor industry, where they are used to drain highly corrosive liquid waste. When exposed to oxidizing environments, thermoplastic pipes can undergo stress-corrosion cracking (SCC), potentially causing them to fail prematurely in the absence of appropriate design and maintenance guidelines. Here, the stress-corrosion cracking behavior of polypropylene, commonly used in waste drainage pipes for dilute sulfuric acid/hydrogen peroxide mixtures (Piranha solutions), is investigated as a function of applied energy release rate. Sub-critical crack growth experiments are performed with compact tension specimens in sulfuric acid/hydrogen peroxide mixtures using a custom constant-force loading system to evaluate the effects of temperature and chemical composition on SCC crack growth. The activation energy for the SCC process is 99.7 ± 15.3 kJ/mol, and the crack growth rate depends sensitively on the concentrations of sulfuric acid and hydrogen peroxide in the mixture. We propose a practical guideline to calculate the service life of polypropylene pipes in Piranha solutions using crack velocity curves and show that accidental exposure to a concentrated Piranha solution can significantly reduce service life.
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- Award ID(s):
- 2011754
- PAR ID:
- 10500469
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Extreme Mechanics Letters
- Volume:
- 64
- Issue:
- C
- ISSN:
- 2352-4316
- Page Range / eLocation ID:
- 102080
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.eml.2023.102080
