October 11, 2001
Production or fabrication processes can include dozens of stages to convert raw materials into finished goods. Regardless of the raw material or the finished product, one factor is constant - - most metals look alike.
Production or fabrication processes can include dozens of stages to convert raw materials into finished goods. Regardless of the raw material or the finished product, one factor is constant - - most metals look alike. Without a method for identifying a particular alloy, it is impossible to be sure that it is the correct material for the corresponding finished product.
Analyzing materials with a nondestructive test instrument in accordance with a standard operating procedure (SOP) can help ensure consistent delivery of parts with the correct alloy composition and prevent expensive field replacement and associated downtime.
An SOP for alloy analysis should include at least six components. These are positive material identification (PMI), inspection frequency, test methods, acceptance criteria, marking and documentation, and resolution of discrepancies.
PMI. Several organizations have published guidelines for PMI programs, including the Pipe Fabrication Institute (PFI Standard ES-42); the American Petroleum Institute (API Recommended Practice 578); and the American Society for Testing and Materials (ASTM Standard E1476-97). These protocols cover the testing of raw materials, in-process parts, and finished goods.
Inspection Frequency. Inspection frequency depends on several factors, including customer requirements, whether the incoming material has a mill test report (MTR) and a heat stamp, and the ultimate use of the finished product. As the API Recommended Practice 578 states, "For higher-risk systems ... consider the need for employing a higher percentage of examination (up to 100 percent) rather than random sampling, which may be more appropriate for lower-risk systems."
Test Methods. Test methods should include the type of analytical instrument to be used, maintenance requirements for the device, training requirements for the operators, specified testing times for unique alloy or sample types, and the frequency of calibration of the instrument. It also should include the locations (or stations) within the manufacturing process where testing is to be performed. The procedure should stipulate testing at the receiving area, at several stations within the manufacturing process, and before shipping the finished goods.
Acceptance Criteria. Acceptance criteria may be based on confirmation of the nominal amounts of alloying elements specified for the particular alloy. Alloy specifications are available from the Unified Numbering System (UNS), which is published jointly by the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE); American Society of Mechanical Engineers (ASME); or industry trade groups.
Marking and Documentation. After the alloy has been identified, the material's label or mark should encompass either color-coding all pieces of material by alloy or imprinting (via a low-stress stamp) a mark identifying the alloy in each piece.
Documentation can include the name of the company and individual performing the tests, copies of certificates documenting factory training for the instrument operator, instrument serial number and standardization data, the date and time of each test, and the results of each test. The documentation should include the MTR, which supplements the empirical data gathered from the testing procedures.
Resolution of Discrepancies. When discrepancies occur, recalibration of the instrument and retesting the subject piece are necessary. If a discrepancy still exists, a second instrument can provide verification, or an outside laboratory can provide a more thorough analysis.
OSHA has published Compliance Guidelines and Recommendations for Process Safety Management (non-mandatory) - 1910.119 Appendix C for standard criteria for external (alloy) inspections. This standard covers piping and vessels, and gives codes and methodologies for internal and external inspections, plus an in-service frequency formula derived from specific alloy corrosion rates. Companies need to develop testing procedures to ensure that inspections are conducted effectively and that product consistency is maintained throughout the manufacturing process.
The Food & Drug Administration (FDA) also requires that all facilities that manufacture regulated products apply extensive installation qualification (IQ) and operational qualification (OQ) procedures. Section 820-30H (Design Changes) of its code requires each manufacturer of pharmaceutical products to establish and maintain procedures for the identification, documentation, validation, and verification of all systems and products used in the manufacturing process.
It is important that equipment operators be familiar with the test instrument's capabilities and limitations. They should be trained thoroughly in the use of the instrument, and must adhere to the manufacturer's suggested calibration schedule.
If a test instrument that incorporates XRF (X-ray fluorescence) technology is used, standardization should include the measurement from a calibration check sample, such as 1-1/4 chromium (Cr) -1/2 molybdenum (Mo), upon start-up, at least every two hours of use time, and before instrument shutdown.
For more precise documentation of instrument performance, the instrument is tested against standard samples of known alloys, or certified reference materials (CRMs), which are available from the National Institute of Standards & Technology (NIST) and other certification agencies.
For example, when inspecting a shipment of 321 stainless steel for use in a petrochemical refinery, the operator verifies the instrument's calibration by testing a 321 stainless steel CRM before initiating the test sequence, and after testing before accepting the lot.
Establishing an SOP doesn't have to be a complicated task. Simplifying this process is a matter of addressing each aspect of the process - PMI, inspection frequency, test methods, acceptance criteria, marking and documentation, and resolution of discrepancies - in sequence.
In addition, complying with any regulatory requirements for the finished product's intended use and ensuring that operators are familiar with the use of the test instrument help to prevent material mix-ups.
Written by Jonathan Shein, Vice President Sales, at firstname.lastname@example.org by Andrea Kinney, Research Scientist, at the Niton Corp. Niton manufactures a variety of XRF instruments for lead testing, coating analysis, and alloy analysis for manufacturing, environmental, mining, and precious metals applications.