In refineries and petrochemical plants, frequent contact with process media can result in premature corrosion of valves and related components. To help prevent this, vendors can provide expert advice and, in some cases, lab testing to verify compatibility between wetted parts and process media.
Below is a summary of our article in the August 2023 issue of Hydrocarbon Processing, titled “Select the Appropriate Construction Materials for Valves and Accessories,” which discusses some of the challenges of valve material selection, and shows how valve vendors can help.
Material selection challenges
The interactions between wetted parts and process media can be quite complex, so selecting appropriate construction materials requires a great deal of expertise. One common cause of improper selection is the presence of contaminants, which are often not detailed in a safety data sheet (SDS).
Improper selection often leads to premature failure and results in downtime because replacement may require shutting down at least part of the process. It also poses a health risk to personnel, as chemical attack from the process media may emit hazardous fumes.
Vendor Solutions
Valve vendors typically have experts in-house that examine each SDS to provide material recommendations, which works well in most, but not all, cases. To make a fully informed recommendation, vendors must be aware of the state of process media and the presence of contaminants at every process stage—not just steady state.
In addition to materials expertise, some vendors also offer lab testing services, in which wetted component parts are exposed to process media over a period of time to detect unwanted interactions. Between consultation and testing when required, most material selection pitfalls can be avoided.
However, there is a rare but potentially serious form of failure that often goes undetected in the process industries—liquid metal embrittlement (LME).
Understanding LME
LME occurs when certain liquid metals—such as mercury, gallium, and indium—come into contact with susceptible ductile metals. This phenomenon reduces the ductility of the affected metal, leading to cracking under stress.
The possibility of LME, especially caused by mercury, should be considered during materials selection, as some process media, including natural gas and crude oil, may contain mercury. In addition, mercury released into the atmosphere from industrial and natural sources can be deposited on metal surfaces.
Filter assembly failure
After less than ten months in service, plant personnel at a petroleum refinery observed cracking on a brass filter assembly case. Upon investigation, it became clear that LME caused the failure. Inspection with a digital microscope showed silvery particles scattered near the cracks.
Scanning electron microscope (SEM) observations and semi-quantitative energy dispersive X-ray (EDX) microanalysis confirmed that the silvery particles were in fact mercury. Mercury was found within the crack and on all areas on the surface under evaluation.
Consult your vendor
Material selection of wetted components can be challenging, especially because process media contaminants can result in unforeseen interactions. Vendors consultation and testing reduces the risk of premature failure, helping end users improve safety, uptime, and regulatory compliance.
Want to learn more about Emerson products, services & industry solutions we offer? Engage with an expert today and let us know how we can assist you.
About the authors:
Ali Babakr is a Senior Principal Materials Engineer for research and development at Emerson. Dr. Babakr has previously held various positions with Emerson and other companies as a subject matter expert dealing with metallurgical and failure evaluation, material selection and corrosion studies. He has a field experience in the petroleum and petrochemical industries, and he participates in various ASTM and AMPP subcomittees. Dr. Babakr holds an MS degree and PhD in metallurgy from the University of Idaho, and a BS degree in chemistry from Houston-Tillotson University in Austin, Texas.
Jim Griffin is a Director of research and development at Emerson. Dr. Griffin has more than 30 years of experience in materials, accoustics, cavitation, flame detonation, additive manufacturing and pressure regulator design. Dr. Griffin earned his PhD in nuclear engineering from the University of Missouri – Columbia, and an MS degree in the same specialty from the Massachusetts Institute of Technology. He also holds a BS degree in nuclear engineering from the University of Buffalo, and an MBA degree from the University of Iowa.
