API 939-C: What Is It? How Do I Comply?

API RP 939-C-known as API 939-C for short-is the American Petroleum Institute’s recommended practice regarding sulfidic corrosion of piping and other components in the petroleum refining industry. The title of this recommended practice is “Avoiding Sulfidation Corrosion Failures in Oil Refineries.” API 939-C is a subsection of API RP 578 which recommends a 100% PMI (positive material identification) program in petrochemical refineries, meaning that all alloy grades have to be verified to meet specifications. Both the overall PMI mandate and the mandate to check alloy compositions to avoid sulfidation corrosion failures are crucially important to the petrochemical industry, as failures in refinery piping and components can be extremely costly, resulting in plant down-time, extensive damage to infrastructure, injuries, and sometimes even casualties.

What Causes Sulfidation Corrosion Failures in Oil Refineries?

While there are several factors that influence the rate of sulfidation corrosion including temperature, heat transfer conditions, etc., the alloys used in the piping and components play a major role. As a function of alloy composition, sulfidation corrosion occurs as a result of one of two circumstances:

  • Exposure of steels to H2S (hydrogen sulfide) and to hydrogen-free (also called H2-free)  process streams where hydrocarbons with sulfur compounds are present. The lower the chromium (Cr) content of the steel alloy, the faster the rate of corrosion. For example, carbon steel components do not hold up well, and not at all H2S streams; Cr5 holds up somewhat better, Cr9 even better, etc.; Cr18 (stainless) is virtually insusceptible to sulfidic corrosion.
  • Exposure of carbon steels with silicon (Si) content below one tenth of a percent-or 0.1%-to H2-free process streams in which sulfur compounds are present. These low-Si carbon steels will corrode significantly faster than their carbon steel counterparts with higher Si content.

The ability to readily obtain and quantify the composition of steel alloys-specifically levels of Cr and low levels of Si—is therefore essential to running a safe, productive oil refinery operation.

XRF Steel Analysis with the Bruker S1 TITAN to Help Prevent Sulfidation Corrosion

The Bruker S1 TITAN has the ultimate performance characteristics for detection and quantification of Cr and Si in steel, even at 0.10%. The powerful x-ray tube and state-of-the-art silicon drift detector in the Bruker S1 TITAN allow for results to be obtained easily, quickly, and completely nondestructively, even at the low elemental concentrations required to verify carbon steel components for sulfidic corrosion prevention. The Bruker S1 TITAN boasts the following additional benefits, allowing you to find peace-of-mind regarding the likelihood of sulfidic corrosion at your oil refinery:

  • Lightweight, handheld instrument can analyze piping and components with ease at all steps of the process and in any location, from the time you receive parts from a manufacturer, to checking inventory for the availability of correct components, to spot-checking in-process components
  • Unparalleled accuracy
  • Near-laboratory quality results in a fully portable, easy-to-use instrument

A 100% PMI protocol is important to the safe and profitable operation of any petrochemical plant. The analysis of carbon steels for low levels of Si with a handheld XRF PMI gun is now a possibility thanks to the S1 TITAN, in full compliance with API 939-C.

Contact Bruker today to have one of our specialists who knows your business answer your questions or provide an equipment demonstration at your work site.

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