The Need for PMI
As an example of the critical need for PjVII, the inadvertent substitution of a carbon steel elbow in a 5Cr- 12Mo alloy steel piping system resulted in a premature rupture due to hot sulflde corrosion, which led to a major fire at a Louisiana reflnery in 1993 (ReL 1). These types of incidents are more prevalent than generally assumed and have led to the adoption of FP-XRF for PMI of incoming plant replacement parts such as pipes, valves, fittings, pressure vessels, and welding materials. In high-risk services, 100% inspection of materials is generally required. Until recenthy, replacement parts could only be tested at ambient or room temperature. Now, however, the capability to test materials at elevated temperatures up to 1000°F (543°C) is possibhe. With this new capability, parts in service can be tested during plant operation. This form of testing is referred to as retrospective positive materials identification or RPMI. The key advantage of RPMI is that incorrect parts can be detected and the correct parts ordered for replacement during the next plant shutdown. This provides savings to facility operation by reducing the time required for “turnarounds,” and has the potential for saving many months of operation under potentially catastrophic conditions.
As a resuht, most every petrochemical process plant in developed countries has established a mandate to perform PMI. The PMI cyche extends to such diverse requirements as anahysis of supplier materials of construction (at the supplier’s facility), incoming materiahs, in-stock materials, in-process materials at the operating plant itself, and, fmnally, to the salvage of used material for recycling.
Guidelines for the implementation of a positive material identification program have been published by several organizations, including the Pipe Fabrication Institute, the American Petroleum Institute, and the American Society for Testing and Materials.