Mechanical integrity of piping systems is the leading source of failures in the hydrocarbon processing industry. But how is the integrity of the pipe compromised? A leading cause is sulfidic corrosion.
Inspectioneering Journal published an article in their March/April 2013 publication addressing this issue. Carbon steels with low silicon (<0.10%) content have been shown to corrode at an accelerated rate when exposed to sulfidation corrosion conditions. In fact, According to the American Petroleum Institute (API) Recommended Practice 939-C (Guidelines for Avoiding Sulfidation Corrosion Failures in Oil Refineries), one-third of high-temperature sulfidic corrosion failures are the result of low silicon content in piping.
Those failures can result in leaks, early replacements, unplanned outages, and incidents potentially resulting in loss of property and injury to workers. In August of 2012, release of flammable vapor led to a massive fire at a refinery in Richmond, California. A report, prepared by a metallurgical laboratory in California, concluded that the 8-inch steel pipe, from a section designated as 4-sidecut which was installed in 1976, ruptured due to severe sulfidation corrosion, and that tested pipe samples showed a very low concentration of corrosion-inhibiting silicon. The Chemical Safety Board (CSB) Chairperson Rafael Moure-Eraso said, “The report, resulting from a cooperative effort between the CSB, Cal/OSHA, the United Steelworkers (USW), and Chevron provides a solid, technical basis for the firm conclusion that the pipe corroded over time from sulfidation corrosion. We hope this report receives widespread attention throughout the petrochemical industry as a precaution to all refiners to carefully examine potential corrosion mechanisms and use the safest possible materials of construction to avoid failures. Refineries and other plants must incorporate strong mechanical integrity and inherently safer strategies in their process safety management programs.”
There are other factors that can cause corrosive thinning of pipe walls, like sulfur content of the oil, temperature, and flow rate. However, silicon content below 0.1% has been shown to significantly increase the rate of sulfidation corrosion. One study from the Second International Symposium on the Mechanical Integrity of Process Piping [January 1996, Houston, TX, USA] found that “41% of the 170 largest losses in the hydro-carbon process industry resulted from failures of piping system.”
In an effort to reduce failures, OSHA began a Refinery National Emphasis Program (CPL 03-00-004) in 2007. The API also has Recommended Practice-API RP-578 (Material Verification Program for New and Existing Alloy Piping Systems) for the same reason. In 2011 OSHA expanded their refinery program to cover nearly all manufacturers of hazardous chemicals under NEP CPL 03-00-014. Both of these programs require a rigorous process safety management system with positive material identification (PMI) as a key element of such a program. [API RP 939-C is a subcomponent of the larger API RP 578 (Material Verification Program for New and Existing Alloy Piping Systems) Positive Material Identification (PMI) program – the verification of correct alloy installation in all sulfidation surfaces, both proactive and reactive.]
Today’s best practices include 100% positive material testing of all critical materials, including piping systems.
The next article will address how X-ray fluorescence (XRF) inspection of piping systems can reduce sulfidation corrosion risk.