Heat treatment is the industry where the maintenance system is the compliance system. A batch of aerospace forgings, automotive gears, or medical implants only ships if the pyrometry records prove the furnace was in specification — and those records are entirely a function of thermocouple calibration cadence, System Accuracy Tests after every maintenance, and Temperature Uniformity Surveys scheduled by class. Miss one and every batch since the last valid test is in question. An heat treatment plant CMMS demo — book a free Oxmaint walkthrough shows the workflow.
The AMS 2750H Class Matrix
Furnace Class Decides Everything. One Lookup, Six Cadences.
Aerospace pyrometry (AMS 2750H) · every class carries its own inspection rhythm
Furnace class
Tolerance
Typical process
TUS frequency
SAT frequency
TC cal
Class 1
±3°C
Aerospace critical · superalloys
Monthly
Weekly
3 months
Class 2
±6°C
Aerospace structural · Ti alloys
Quarterly
Bi-weekly
6 months
Class 3
±8°C
General aerospace · tool steels
Quarterly
Monthly
6 months
Class 4
±10°C
Commercial · automotive gears
Semi-annual
Monthly
Annual
Class 5
±14°C
General industrial
Semi-annual
Quarterly
Annual
Class 6
±28°C
Preheat · low criticality
Annual
Quarterly
Annual
Reward mechanic
Four consecutive successful TUS passes on a Class 2 furnace can extend the interval from monthly to quarterly. Every extension needs the evidence trail to justify it.
TUS vs SAT: Two Tests, Two Purposes, Both Non-Negotiable
TUS and SAT are the two AMS 2750H tests that every heat treatment auditor asks about first — and they get confused in the field constantly. TUS proves the whole furnace work zone holds temperature uniformly, in 3D, across the entire qualified volume. SAT proves that the specific permanent thermocouple and controller loop is still reading accurately at a single point. Different tests, different equipment, different failure modes. A CMMS that treats them as one calendar reminder loses the plot; a CMMS that models each as its own work order stream against each affected instrument catches the drift Nadcap auditors look for. Teams evaluating the TUS + SAT dual workflow can book a free demo of the pyrometry evidence module.
TUS vs SAT — Same Furnace, Different Tests
TUS
Temperature Uniformity Survey
Tests the whole work zone volume · grid of calibrated thermocouples placed on a survey rack · furnace heated to survey temperature and held for defined soak period · verifies every part of the load sees the same temperature within class tolerance
Measures3D uniformity across work zone
SensorsMultiple calibrated test TCs
TriggersSchedule by class · after major repair
SAT
System Accuracy Test
Tests one permanent thermocouple and its controller loop · reference TC placed adjacent to the permanent TC · reading compared against the reference · verifies the permanent measurement loop is still accurate at that point
MeasuresPoint accuracy of one TC loop
SensorsOne reference TC + field instrument
TriggersSchedule by class · after ANY maintenance
The After-Maintenance SAT Trigger Loop
The most common Nadcap finding in aerospace heat treatment audits is a missed post-maintenance SAT. A technician replaces a heating element, changes a thermocouple, or repairs a door seal — and the SAT that AMS 2750H requires before the next production run does not happen because the maintenance work order and the SAT requirement live in different systems. The CMMS that links every furnace maintenance event to an automatic SAT trigger closes this loop by design. Teams evaluating this loop in a live workspace can book a free demo of the SAT trigger workflow.
Post-Maintenance SAT Trigger — When It Fires
TC
Thermocouple replacement
SAT required before next production batch · new TC verified against reference before release
HE
Heating element replacement
SAT required · heat delivery pattern may have shifted · furnace requalification cadence checked
CT
Controller change or update
SAT required · full instrumentation calibration chain re-verified
DS
Door seal or refractory repair
SAT typically required if repair affects work zone temperature stability · SAT judgement flag
QT
Quench system service
SAT not required for furnace loop · but quench temperature and agitation verification separately triggered
AT
Atmosphere generator maintenance
SAT not directly triggered · but carbon potential verification cycle scheduled before next carburising run
Thermocouple Lifecycle: The Silent Drift Clock
Every thermocouple in the plant is on its own calibration clock, and every use case has different tolerances. A thermocouple used for TUS reference work has to be more accurate than one used for load control, which has to be more accurate than one used for atmosphere sensing. Different maximum permitted errors, different recalibration intervals, different usage limits. AMS 2750H Table 2 and CQI-9 process tables both spell this out — and both punish plants that treat all thermocouples as one class.
Thermocouple Use Cases — Different Rules Per Function
Primary calibration TC
±1.0°C
6 months
Highest accuracy · calibrates other TCs · limited uses per year
TUS reference TC
±1.1°C
3–6 months
Used for uniformity surveys · calibrated before each TUS
SAT reference TC
±1.1°C
6 months
Used for system accuracy tests · calibrated regularly
Load control TC
±2.2°C
Per class · replace on drift
Runs with production load · usage-limited before replacement
Permanent control TC
±2.2°C
Verified via SAT
Fixed in furnace · never removed for calibration · verified in-situ
Atmosphere sensing TC
Process-specific
Per process table
CQI-9 process-specific rules apply · not covered by AMS 2750
See a Live Heat Treatment Plant Workspace
Watch a 30-minute demo of Oxmaint configured for furnaces, quench systems, atmosphere generators and TCs — with AMS 2750H and CQI-9 evidence trails built in.
Beyond the Furnace: Quench and Atmosphere Assets
Furnaces get the audit attention, but quench systems and atmosphere generators are where the metallurgical failures actually happen. Quench oil viscosity, agitation, and temperature all shift with maintenance state — and each shift changes cooling rates enough to move a part from within tempering spec to outside. Atmosphere generators driving endothermic or exothermic gas for controlled-atmosphere carburising demand their own calibration chain, separate from the AMS 2750H pyrometry loop. A CMMS that treats these as first-class assets alongside the furnace closes the gap. Teams new to holding quench and atmosphere assets in one workspace can sign up free to explore the metallurgical asset structure before rolling across the plant.
Quench + Atmosphere — The Assets AMS 2750H Does Not Cover
Quench oil tank
Viscosity · temperature · water contamination · flash point
Weekly sampling · monthly full analysis
Cooling rate drift · part hardness variation
Agitator + circulation
Flow rate · direction · agitator bearing condition
Weekly inspection · vibration monthly
Uneven quench · differential hardness across load
Salt bath
Composition · temperature · sludge accumulation
Bi-weekly composition test
Chemistry shift · surface finish defects
Endothermic generator
Carbon potential · dew point · catalyst condition
Continuous CP monitoring · monthly catalyst check
Carburising case depth variation
Expert Perspective: The Audit Trail Is the Product
In heat treatment, particularly for aerospace and medical work, the pyrometry documentation trail is functionally part of the product. A Nadcap auditor walks the plant and asks three questions: show me the TUS records for this furnace, show me the SAT records since the last TUS, show me the thermocouple calibration history for every TC in this furnace. If those answers live in three separate binders and one supervisor's memory, the audit finding writes itself. The heat treatment plants that pass without stress hold every pyrometry event — TUS, SAT, thermocouple calibration, post-maintenance triggers — inside one system where the linkage between the maintenance event and the required follow-up test is automatic, not procedural.
Class
Class-driven cadence engine
Furnace class → TUS + SAT + TC cadence auto-configured · reward-mechanic extensions handled automatically.
Trigger
Post-maintenance SAT trigger
Every maintenance work order carries pyrometry impact flag · SAT auto-scheduled before next production release.
Chain
Calibration evidence chain
Every TC · every calibration · every certificate · linked to the furnace and to the batches it processed. Audit-ready.
UK Heat Treatment Context: Nadcap, Aerospace and Automotive
The UK heat treatment sector sits at the centre of a demanding customer environment. The aerospace supply chain — Rolls-Royce, BAE Systems, Airbus UK, GKN Aerospace — expects Nadcap accreditation and full AMS 2750H compliance evidence. The automotive supply chain — JLR, BMW MINI Oxford, Nissan Sunderland — expects CQI-9 self-assessment records at every audit. Contract heat treaters serving both need one CMMS backbone with two evidence filters. Any plant serving medical device work adds ISO 11135 sterilisation validation on top. To scope this against your UK operation, book a free demo aligned to Nadcap and CQI-9 requirements.
01
Nadcap AS7102 evidence
Aerospace primes expect pyrometry, process control, and calibration evidence discoverable per Nadcap checklist without a reconstruction exercise.
02
CQI-9 for automotive supply
Automotive customers require CQI-9 self-assessment records annually. Process tables A–H evidence filtered per assessment scope.
03
Contract heat treat multi-audit
Serving aerospace + automotive + medical means three parallel audit programmes. One evidence backbone, filtered per standard, avoids fragmented documentation.
A Realistic Rollout for a UK Heat Treatment Plant
A heat treatment CMMS rollout should follow the compliance risk. Pyrometry compliance first — because that is what the audit floor requires. Quench and atmosphere second — because that is where metallurgical failures happen. Utilities and support last. A phased plan captures AMS 2750H evidence value inside the first month.
Weeks 1–4
Pyrometry compliance
Furnace asset register + class assignment
TUS + SAT cadences configured per class
Every TC held as individual asset
Post-maintenance SAT trigger live
Weeks 5–8
Quench + atmosphere
Quench tank sampling cadence live
Agitator + circulation PMs configured
Atmosphere generator monitoring
Carbon potential verification cycles
Weeks 9–12
Audit + reward
Nadcap AS7102 evidence pack
CQI-9 process tables A–H filters
TUS extension reward mechanic tracked
Multi-standard audit filters set up
Bring Every Pyrometry Record Onto One Audit-Ready Screen
Let Oxmaint show you a heat treatment workspace configured for your furnaces, quench, atmosphere and thermocouples — with AMS 2750H, CQI-9 and Nadcap evidence built in.
Frequently Asked Questions
Can Oxmaint configure furnace-class-driven TUS and SAT cadences automatically?
Yes. Each furnace carries an assigned AMS 2750H class or CQI-9 process table reference, which drives the TUS and SAT cadence directly — no manual scheduling per furnace. When a furnace completes consecutive successful TUS passes and qualifies for the AMS 2750H reward-mechanic extension (for example, monthly to quarterly on a Class 2 furnace), the CMMS updates the cadence and retains the evidence chain justifying the extension. Downgrades on failed passes are handled with the same automation.
How does the post-maintenance SAT trigger actually work?
Every furnace maintenance work order carries a pyrometry impact flag. Thermocouple replacements, heating element changes, and controller updates automatically trigger a blocking SAT work order that prevents the furnace from releasing to production until the SAT passes. Door seal repairs and refractory work carry a judgement flag prompting technician decision. Quench and atmosphere maintenance follow their own separate verification triggers rather than SAT. This is one of the highest-value Nadcap compliance integrations.
Does the platform hold every thermocouple as an individual asset?
Yes. Each thermocouple carries its own asset record with calibration history, certificate, maximum permitted error per use case, usage count, and drift trend. Different rules apply to primary calibration TCs, TUS reference TCs, SAT reference TCs, load control TCs, and permanent control TCs. Overdue calibrations flag as blocking events on any asset that uses the TC. Full TC history is retained for aerospace pyrometry audit evidence and quality investigation.
Can we manage quench oil sampling and atmosphere generator monitoring alongside furnace PM?
Yes. Quench tank sampling cadences (viscosity, temperature, water contamination, flash point) are held as scheduled work orders against the quench tank asset. Atmosphere generator monitoring (carbon potential, dew point, catalyst condition) is held against the generator with continuous parameter tracking where controller integration is available. Both operate alongside the AMS 2750H pyrometry loop for the furnace, giving one full asset picture for the metallurgical process rather than fragmented records.
Does the CMMS support both Nadcap and CQI-9 evidence filtering?
Yes. Contract heat treaters serving both aerospace and automotive sectors can filter evidence per standard on demand — Nadcap AS7102 checklist scope for the primes, CQI-9 process tables A–H scope for the automotive supplier audits, and additional filters for ISO 11135 medical device work if applicable. One underlying evidence backbone, multiple audit lenses, no fragmentation. This transforms the audit experience from a reconstruction scramble into a documented, filterable process.
