AWS A4.2M/A4.2 PDF

This standard prescribes procedures for the calibration and maintenance of calibration of instruments for measuring, by magnetic attraction or permeability, the delta ferrite content of an austenitic or duplex ferritic-austenitic stainless steel weld metal in terms of its Ferrite Number (FN).

A thorough review of the Annex is recommended before any instrument is calibrated or used. The Annex presents background information which is essential to understanding the many problems and pitfalls in determining and specifying the ferrite content of weld metals.

Calibration can be accomplished with the use of the National Institute of Standards and Technology (NIST, formerly National Bureau of Standards) primary standards or weld-metal-like secondary standards. At the present time, only three instruments (Magne-Gage [including a torsion balance using essentially a Magne-Gage No. 3 magnet, hereinafter referred to as a Magne-Gage-type instrument], Feritscope Model FE8-KF (Footnote 1), and Inspector Gage) (Footnote 2) can be calibrated by the use of NIST primary standards and the values in Tables 1, 2, or 3 in this document. The range of possible calibration depends upon the particular instrument. This is not an endorsement of any particular instrument (see 3.1).

Some manufacturers may not calibrate their instruments to A4.2. Therefore, if calibration to A4.2 is required, it is the responsibility of the user of the instrument that this calibration be performed.

Footnote 1 - This is a pre-1980 instrument. Post-1980 models and the current models, now identified as Feritscopes, cannot be easily calibrated with the NIST primary standards and the tables in this document. See Section 5.

Footnote 2 - These instruments were selected for testing from several similar instruments by the Welding Research Council's Subcommittee on Stainless Steel Welding. Each instrument was extensively tested to develop the data shown in Tables 1, 2, and 3. This standard contains those data and instructions for their use. For information or requests regarding the ability of other instruments to be calibrated to NIST Primary Standards, contact the Welding Research Council, 345 East 47th