Across mid-size fabrication operations in steel, pipe, and pressure equipment, roughly 8–15% of incoming mill test certificates carry at least one discrepancy when compared against the applicable specification or the purchase order. That means on a receiving day with 50 MTCs, between 4 and 8 of them have something wrong.
Most fabrication shops don't know their rejection rate because they don't track it. MTCs with problems either slip through undetected or get resolved informally — a phone call to the supplier, a note in the file — without creating any systematic record. The rejection log is empty because nobody is filling it in.
The consequence of not knowing your rejection rate is that you can't reduce it. You can't identify which suppliers consistently produce problem certs. You can't show improvement over time. And you can't use the data to have a meaningful corrective action conversation with a supplier.
Common Rejection Reasons and Their Frequency
When fabrication operations implement structured MTC review and begin logging rejections, the distribution of issues typically looks like this:
Missing required fields (25–35% of rejections). The cert is incomplete — no heat number, no test method reference, no heat treatment condition, no supplementary requirement results that were invoked on the PO. Missing fields are the most common discrepancy because many mills and service centers produce certs from templates and not all template fields are filled in for every order.
Grade or specification mismatch to PO (15–25% of rejections). The product spec or grade on the MTC doesn't match what was ordered. This includes substitutions made without notification, data entry errors in the mill's certification system, and certs pulled from a different order and attached to the wrong shipment.
Values out of specification (10–20% of rejections). Chemistry or mechanical values that don't meet the specification minimums or maximums. This is the rejection type that receives the most attention because it represents a potential material nonconformance — but it's actually less common than documentation issues.
Wrong heat number or illegible heat number (10–15% of rejections). The heat number on the MTC doesn't match the bundle tag, packing list, or the heat number stamped on the material. Or the heat number is present but illegible due to scan quality.
Missing signatures or certification statements (8–12% of rejections). The cert lacks the mill's authorized representative signature, or the certification statement is absent or incomplete.
Supplementary requirements not documented (8–12% of rejections). Supplementary requirements were invoked on the PO but don't appear on the MTC.
Categorizing Rejections: Three Tiers
Not all rejections require the same response. An effective rejection management process uses three categories:
Critical — Hold material. The discrepancy indicates the material may not meet the specified requirements, and the material cannot be used until the discrepancy is resolved. Examples: values out of specification, grade mismatch to PO, heat number that doesn't match physical material identification. Material with a critical rejection goes to a quarantine area with a hold tag. It does not enter the shop floor. Resolution requires either a corrective MTC from the mill confirming the correct data, replacement material, or a formal engineering disposition.
Major — Supplier correction required. The cert is incomplete or has documentation errors, but the material may be correct. Examples: missing supplementary requirement results, missing heat treatment documentation, missing signatures. The material can be received into a conditional hold status, but a corrected cert must arrive from the supplier before the material is released to fabrication. Resolution timeline: typically 24–72 hours for a corrected cert from an established supplier.
Minor — File note. The cert has a documentation gap that doesn't affect the material's compliance and can be resolved with a simple clarification. Examples: illegible field that can be verified against the packing list, missing reference to a general requirements standard that is implicit in the product spec. Minor rejections are documented in the rejection log and communicated to the supplier as a quality note, but they don't create a material hold.
Building a Rejection Log That Feeds Supplier Scorecards
A rejection log has five fields: date, supplier name, PO number, rejection category (critical/major/minor), and rejection reason. That's it. A shared spreadsheet works for operations that review fewer than 200 MTCs per month. A quality management system is more appropriate above that volume.
Monthly, the rejection log produces three metrics per supplier: rejection rate (rejected MTCs as a percentage of total MTCs received), critical rejection rate (critical rejections only), and rejection reason breakdown by category. These metrics go into the supplier scorecard.
Suppliers with consistently high rejection rates or recurring critical rejections receive a formal supplier corrective action request (SCAR). The SCAR documents the pattern, requests root cause analysis and corrective action from the supplier, and sets a 30-day response deadline. The rejection log data is attached as evidence.
For suppliers with chronic issues that persist through two SCAR cycles, the appropriate response is qualification review — either additional incoming inspection requirements (100% inspection vs. normal sampling) or removal from the approved supplier list.
What Reducing Rejection Rates Actually Looks Like
A fabricator with a documented 12% MTC rejection rate in Q1, after implementing structured review, supplier SCARs, and monthly scorecard reviews, typically reaches 5–7% by Q4. Reduction below 5% requires supplier process improvement at the mill level — most persistent issues above that floor are resolvable through the SCAR process.
The reduction in rejection rate doesn't just mean cleaner paperwork. Each critical rejection that's caught at incoming rather than discovered downstream prevents a potential quality event. At the median fabrication shop, one downstream quality event per year is attributable to a cert discrepancy that cleared incoming. That event costs an average of $25,000–$75,000 in rework, delay, and customer remediation.
The prevention value of reducing critical rejection rates by half — typically achievable in 6 months with systematic tracking — exceeds the cost of the tracking program within the first year.