Positive Material Identification (PMI) emerged as a common customer requirement in the 1990’s as X-Ray Fluorescence (XRF) instrumentation became mobile. It can be a confusing and misunderstood requirement. This paper is an effort to provide some clarity to the requirement, the cost involved and steps required to comply with customer requirements.
When considering PMI, there are several key factors that must be clarified prior to quotation. Following is an outline of how reduce the requirement to a manageable task.
There are three primary considerations:
Elements to be Tested
- Alloy Verification – This is most common and will identify the material via key alloying elements. It is only applicable to materials generally classified as “Alloys”, such as stainless steel (304 SS, 316 SS, etc.), high nickel (Hastelloy® C, Inconel®, etc.) or high chrome alloys (P91, F22, etc.) carbon steels (SA-105, SA-106, SA-696, etc) are excluded from the “Alloy Verification” requirement. i. Note: To differentiate “L” grade stainless steels a full spectrum analysis must be performed.
- Full Spectrum Analysis: This would include carbon steels. A key phrase to watch for is “ALL elements with an atomic element above 16…”
Parts to be Tested
- Pressure Bearing Parts: This would include chambers, covers, valve bodies and pipe.
- Weld deposition: This is to verify that the correct weld filler material was used.
- Fasteners: Usually SA-193 B7 fasteners, although high chrome alloy, are exempted. This is a key point as Questtec uses so many bolts.
Percentages to be Tested
This is often stated as 100%. But if the other two factors are not identified, the cost cannot be determined prior to quoting. Often times there will be different requirements for different parts.
When an RFQ is received stating simply “PMI, 100%”, further clarification is absolutely required. The cost could easily range from several hundred dollars to many thousands of dollars. If it is impossible to get further clarification, offer the following with your quotation as the Questtec standard scope:
“Positive Material Identification shall be applied 100% to pressure boundary parts and welds in contact with the process media, such as gauge chambers, piping, valve bodies and weld deposit. The method shall be portable XRF, indicating key metallic alloying elements. SA-193 B7 alloy fasteners are specifically excluded from this scope.”
This simple phrase will meet customer intent in nearly all circumstances.