Imagine concentrations of sulfur and chlorine on the surface of pipe.
Sulfates and chlorides are corrosive to low-carbon steel pipe. A test can identify if sulfur-reducing bacteria is contributing to the failure of the pipe. Bacteria might be found in liquid or soil. Interaction between sulfates and the surface of metal creates a boundary layer of hydrogen. The bacteria oxidizes the hydrogen, creating hydrogen sulfide (H2S). H2S has long been associated with the cause of corrosion damage in high-strength steels and high-hardness weldments used in oil and gas production, petroleum refining and petrochemical processing.
What is corrosion testing?
Corrosion testing is conducted by labs to solve, prevent or mitigate corrosion problems. These tests provide useful information for decisions regarding selection of materials and processing. Proper material selection for piping and equipment helps to avoid future failures. Testing may also reveal opportunities to improve performance.
Routine testing used in industrial applications is required to verify conformance to quality standards. Immersion testing is the most popular type of corrosion test used to assess materials. It's a versatile process that can be customized to meet specific needs. The testing apparatus exposes the sample to test solutions and then to different physical or metallurgical situations. There are numerous corrosion testing techniques available that help prevent losses.
What is corrosion failure analysis?
Failure analysis involves metallurgical investigations of components, equipment, metals, alloys, coatings, linings and structures, environmental degradation and abuse, metal misapplication and mechanical failure. Such investigations are usually needed in the chemical processing, refining, oil and gas, and pulp and paper industries.
Corrosion leaves behind a pattern that can be analyzed with optical and scanning electron microscopy. A thorough analysis must include information about environmental conditions to which the samples were exposed. When requesting a corrosion failure analysis, be sure to provide answers to questions like, "What was flowing through?", "What are the build specifications?", "How was the process fluid flowing through the assemblies?" and "How were they oriented in relation to the ground?" Material safety data sheets (MSDSs) on materials held in tanks or flowing through each piping assembly could help in understanding contributing factors to the failure.
Corrosion failures of welds occur even when the proper base metal and filler metal have been selected, industry codes and standards have been followed, and welds have been deposited that possess full weld penetration and have proper shape and contour. It is not unusual that, although the wrought form of a metal or alloy is resistant to corrosion, the welded counterpart is not.
The corrosion failure analysis lab process has three steps: identifying the corrosion product; metallographic preparation of sample areas including cleaning, sectioning, grinding/polishing and etching; and analysis of the corroded samples for penetrations or crack surfaces that can yield information about the corrosion mechanism.
Who needs to know?
Of all industrial problems confronting engineers, few are more economically important than the prevention of metallic corrosion and mechanical failure. Corrosion failures cost billions of dollars globally every year. Preventing or reducing corrosion increases the productivity and efficiency of any plant and may save lives.
Consider the equipment, pipeline or facility that you are responsible for. Corrosion testing may aid in reducing repairs, downtime and the risk of a failure. A failure analysis may determine choices for your next turnaround or equipment install, as well as for improving safety. Corrosion testing and corrosion failure analysis provide the advantage for you and your organization.
For more information, visit www.mmtinc.com or call (800) 772-0251.
