What is API RP 578?
The purpose of this recommended practice is to provide the guidelines for a material and quality assurance system to verify that the nominal composition of alloy components within the pressure envelope of a piping system is consistent with the selected or specified construction materials to minimize the potential for catastrophic release of toxic or hazardous liquids or vapors.
This recommended practice provides the guidelines for material control and material verification programs on ferrous and nonferrous alloys during the construction, installation, maintenance, and inspection of new and existing process piping systems covered by the ASME B31.3 and API 570 piping codes. This practice applies to metallic alloy materials purchased for used either directly by the owner/user or indirectly through vendors, fabricators, or contractors and includes the supply, fabrication, and erection of these materials. Carbon steel components specified in the new or existing piping systems are not specifically covered under the scope of the document.
Alloy Substitutions in Carbon Steel Systems
When determining the need to perform material verification on carbon steel systems; the owner/user should evaluate the effect that the process stream could have on substituted alloy materials. In some cases, the substitution of harden able alloy materials in carbon steel piping systems resulted in failure and loss of containment. Examples of such systems include hydrogen sulfide(H2S), hydrofluoric acid(HF), and sulfuric acid(H2SO4) services.
Flow-Accelerated Corrosion or FAC is a well-know source of problems. FAC is a process in which carbon steel piping and components are degraded in the presence of flowing water or steam-water with low dissolved oxygen. See (Appendix Niton Application Bulletin). The research conducted has demonstrated that FAC is a complex process influenced by a number of variables.
They include but are not limited to;
- The composite of steel, principally the alloying elements of Chromium, copper and molybdenum.
- The water chemistry in use, PH, dissolved oxygen, and temperature.
- The flow variables including; fluid velocity, diameter, fitting geometry and upstream influences.
According to PVP-Vol. 338, “Pressure Vessels and Piping Codes and Standards, ASME 1996, of the variables listed above, both laboratory testing and plant experience have shown that the material composition, particularly the Chromium content, is the most important variable influencing FAC.
Roles and Responsibilities
A material verification program for piping systems may involve participation of several groups within the operating plant or the shop of a contractor, vendor, or fabricator. When establishing a material verification program. Consideration should be given to the roles and responsibilities that each group has within the specific organization.
These roles and responsibilities should be clearly defined and documented. Within the operating plant, this can include those groups responsible for purchasing, engineering, warehousing, receiving, operations, reliability, maintenance, and inspection.