MTC-Mill Test Certificate

An MTC (Mill Test Certificate) is the most critical quality document for the procurement and acceptance of boiler tubes. In essence, it serves as proof of traceability, linking the specific batch of steel tubes you receive to the actual test data generated in the steel mill’s laboratory for a particular "heat" (melt) of steel.

For a complete boiler tube MTC, you must verify that each of the following details matches your purchase order (PO) and the physical markings on the products themselves.

Identification and Traceability Information

Heat Number: This is the core of an MTC. It must exactly match the stamping or stenciling found on the ends of the steel tubes or on their attached labels. If the heat numbers do not align, the test data cannot be traced to the specific batch, and the material should be rejected.

Standard and Grade: These must be an exact match. For example, if the PO specifies "GB/T 3087 20#" or "EN 10216-2 P235GH," the MTC cannot simply state "carbon steel boiler tube."

Certificate Type: Confirm that the document is designated as an "Inspection Certificate 3.1" or "3.2" (typically found in the header or another prominent location) and ensure it aligns with the requirements stipulated in your contract.

Test Data

Chemical Composition: Verify that the measured values for elements such as C, Mn, P, S, and Si fall within the ranges specified by the applicable standard. For boiler tubes, the limits for phosphorus (P) and sulfur (S) are generally stricter than those for standard structural steel tubes.

Mechanical Properties: Tensile strength, yield strength, and elongation must meet the minimum requirements set by the standard. For high-pressure boiler tubes, the test temperature and impact energy values from Charpy V-notch impact tests are critical points for verification.

Heat Treatment Condition: Boiler tubes are typically supplied in a normalized or stress-relieved condition. The heat treatment process recorded on the MTC must comply with both the relevant standard and the requirements of the purchase order.

Manufacturing and Inspection Results

Non-Destructive Testing (NDT): If the standard or purchase order requires hydrostatic testing, ultrasonic testing (UT), or eddy current testing (ET), the MTC must include the corresponding test results or confirmation of compliance. Dimensional Inspection: Some MTCs (Material Test Certificates) list actual measured values or declarations of conformity for outside diameter and wall thickness; these must be verified to ensure they fall within the tolerances permitted by the applicable standards.

Validity of Signatures

3.1 Certificates: Must bear the signature and stamp of an authorized QC representative from the manufacturer. Documents featuring only a company seal without the signature of an authorized individual are generally considered invalid.

3.2 Certificates: In addition to the above, these must also be countersigned by a TPI (Third-Party Inspection) inspector.