This coordinated Nadcap system results in a standardized approach to quality assurance and a reduction in redundant auditing throughout the aerospace industry.

Founded in 1993 and currently led by Cyril Vernault of SAFRAN Group, the Nadcap Heat Treatment (HT) Task Group is responsible for:

  • Determining HT Nadcap audit requirements and developing HT Nadcap Audit Criteria (AC)
  • Reviewing and accepting corrective-action responses submitted by auditees in response to audit nonconformances
  • Making the final decision on accreditation
  • Assisting auditees in successfully passing HT Nadcap audits efficiently

The Nadcap HT Task Group conducts audits to the following Audit Criteria (Fig. 1), which can be found in the PRI eAuditNetSM system under Resources > Documents > Audit Criteria > Heat Treating (AC7102). A selection of their top tips for Nadcap HT audit success is described in this article.

  • AC7102: Nadcap Audit Criteria for Heat Treating
  • AC7102/1: Nadcap Audit Criteria for Heat Treating – Brazing
  • AC7102/2: Nadcap Audit Criteria for Heat Treating – Aluminum Heat Treating
  • AC7102/3: Nadcap Audit Criteria for Carburizing
  • AC7102/4: Nadcap Audit Criteria for Gas and/or Ion/Plasma Nitriding
  • AC7102/5: Nadcap Audit Criteria for Hardness and/or Conductivity Testing for Heat Treating
  • AC7102/6: Nadcap Audit Criteria for Heat Treating – Hot Isostatic Pressing (HIP)
  • AC7102/7: Nadcap Audit Criteria for Heat Treating for Induction Hardening
  • AC7102/8: Nadcap Audit Criteria for Heat Treating – Pyrometry
  • AC7102/9: Nadcap Audit Criteria for Sintering
  • AC7102/10: Nadcap Audit Criteria for Localized Heat Treating

 

Perform a Thorough Self-Audit

As part of the Nadcap Management Council (NMC) “Audit Effectiveness” initiative, a requirement to perform self-audits prior to the Nadcap on-site audits was added to Nadcap Operating Procedure 1105 – Audit Process as well as the Nadcap Audit Criteria (AC) back in May 2017.

Consequently, all Nadcap HT auditees are now required to upload the Nadcap self-audit to the PRI eAuditNet system at least 30 days prior to any Nadcap audit. Uploading attachments later than 30 days prior to the actual audit might result in a nonconformance (NCR).

HT Audit Criteria are revised and updated frequently, meaning that it is crucial for the auditee to ensure they are using the current revision of the Audit Criteria when performing their self-audit and all 10 applicable job audits. In addition, auditees are required to address all NCRs found during the self-audit, using a corrective-action system, prior to the actual Nadcap audit.

This information must then be uploaded to the PRI eAuditNet system as part of the self-audit package, which includes several lists (equipment, purchased services, quality personnel and approved heat-treating personnel, Prime customers and specifications, copy of internal general procedures for heat-treat processing, pyrometry, testing/inspection of heat-treated products, organization chart and more).

The three most common NCRs (without job audits) written against the AC7102 baseline checklist all relate to the self-audit. The most up-to-date Top-10 NCRs can be found in the PRI eAuditNet system under Resources > Documents > Public Documents > Task Groups > Heat Treating > Top NCRs.

 

Personnel Training

An inadequate personnel training program –
or one that does not refer to everyone with heat-treating-related responsibilities – might create uncertainty about the personnel proficiency and even lead to the auditor writing NCR(s) against it. Personnel training programs should include documented training to establish a summary; knowledge and experience; initial and periodic evaluation of the competency; exam, observation, interview and audit; and cleaning.

 

Cleaning

Cleaning prior to the heat treatment of parts is key to process integrity. Similarly, post-cleaning activity is just as important. Training operators to not touch the parts after cleaning as well as transporting them without touching should be considered because finger marks can destroy properties on certain alloys.

 

Process Control

The Nadcap program requires HT auditees to be able to demonstrate they have reviewed process-control requirements for each of their customers and that they have internal procedures and “systems” that document compliance.

The following testing and controls should also be considered: Pyrometric Testing, Lotly or Periodic Tensile Testing, Periodic Metallurgical Testing, Decarburization/Surface Contamination Testing, Leak-up Rate Testing, Hydrogen Pick-Up Testing, and First-Lot Forging Qualification Testing. Other tests that might apply are specified in AC7102/3 and AC7102/4.

 

Refrigeration of Steels

Where required, Nadcap auditees must have procedures that specify timings, temperatures and tolerances and include requirements for sub-ambient (pH steels requiring <30°C or <20°C). There must also be records of time from quench (if required) and time and temperature achieved.

 

Sampling Plans

It is expected that all heat-treating sampling plans contain a method for the inspector to determine the quantity of product to check in the lot and a specified frequency and method of sampling. This reduces the opportunity for individual interpretation and improves control through consistency.

 

Furnace Control, Maintenance and Start of Soak

Per AC7102, the internal procedure should specify the method for determining heat-up rate, start of soaking time, end of soaking time and cooling rate. It should also include methods/definitions of atmosphere, quench delay and quench residence times.

There are many different ways to define the start of soak. Auditees will either have defined start-of-soak rules that conform to the specifications being used or, where the specifications have no definition of start of soak, have defined the rules that will apply. This is listed as the sixth most common NCR written during Nadcap HT audits.

 

Quench

There are three main liquid quenchants as part of Nadcap HT audits: water, water-polymer mixes and oil. Other quenchants, such as liquid nitrogen and forced air or gas, have been utilized during Nadcap audits.

Most specifications define the acceptable quench-temperature range, with the maximum temperature typically expected to be <=32°C / 90°F at the beginning of the quench process.

A good practice is to ensure the quench tank is ready before loading the furnace. This is crucial because it prevents avoidable delays and related repercussions, which might be an NCR. Similarly, auditees should record the bath temperature before the material touches the liquid as well as the maximum temperature during the quench process. Quenchant maintenance and quenchant agitation should not be overlooked.

 

Racks, Fixtures and Baskets

The location of the racks/fixtures/baskets in the furnace is another crucial aspect that falls under a Nadcap HT audit scope. Using jigs and location guides – such as track guides on the floor, stops inside the furnace, standard racks, etc. – are one approach to ensuring their integrity. Another is to use marks on the furnace itself to show the maximum extent of any load.

 

Pyrometry

There is a whole section in the Nadcap Heat Treatment Audit Criteria dedicated solely to Pyrometry Testing, and AMS 2750 is considered the leading industry specification in this area.

To ensure the general requirement is satisfied, Nadcap auditors will ask whether you have an internal procedure for pyrometry, addressing all the aspects of AMS 2750F – released on June 29, 2020 – and other customer specifications as applicable to your operations.

In an effort to prevent unnecessary issued NCRs, the HT Task Group will not require implementation of AMS 2750F until the implementation of the revised Audit Criteria AC7102/8 Revision A 90 days after its release. If auditees decide to implement AMS 2750F before implementation of AC7102/8 Revision A, they shall not be penalized. However, auditees must demonstrate full compliance to either AMS 2750E or AMS 2750F during the audit; partial implementation is not allowed.

Nadcap AC7102/8 questions address compliance to AMS 2750F on pyrometry, including:

  • Thermocouples
  • Testing instrumentation types
  • Calibration
  • Process recorders/electronic data collection
  • Furnace classes
  • System accuracy tests (SAT)
  • Temperature uniformity surveys (TUS)
  • Load conditions
  • Offsetting

Calibration represents the two most common NCRs written during Nadcap Pyrometry audits, with the third and fourth being in relation to time and temperature data. The top five NCRs are completed by a question regarding the auditee’s internal procedure(s) covering all aspects of AMS 2750E (the AC7102/8 is currently in the ballot process to update information related to the new AMS 2750F).

 

Thermocouples Example

Thermocouples are a good example of the depth of the Nadcap audit. They represent the last four most common top-10 NCRs written during Nadcap Pyrometry audits. Nadcap AC7102 contains questions such as:

  • Are the thermocouples being calibrated throughout the range in which they are to be used?
  • Are procedures in place to ensure that the base-metal thermocouples are only recalibrated/reused when allowed by the AMS 2750F?

Base-metal thermocouples are defined as thermocouple sensors other than noble-metal types B, R and S. It does, however, include types E, J, K, N and T.

 

AMS 2750F

SAE International released the new AMS 2750F – in replacement of AMS 2750E – on June 29, 2020. The Nadcap HT Task Group is currently working on including the changes coming from this new standard revision in the AC7102 series of Audit Criteria and will then proceed with the balloting process before the new Nadcap Heat Treatment Audit Criteria come into effect.

Changes that can be noted cover: definitions, thermocouples and their calibration accuracy, new thermocouples type M and type C, instrumentation, SAT, TUS and quality-assurance provisions. PRI TrainingSM is currently developing its new Introduction to Pyrometry course, which will cover the main differences between AMS 2750E and AMS 2750F.

You can contact us at heattreating@p-r-i.org with any questions you may have about Nadcap Heat Treating audits.

 

COVID-19

As the COVID-19 pandemic evolves, the safety and well-being of all our stakeholders remains the Performance Review Institute’s®, which administers the Nadcap program, highest priority. While the Nadcap program does continue to conduct on-site audits in locations where the situation permits, all parties involved in the program have a shared responsibility to do as much as they can to mitigate the risk to all participants.

Consequently, PRI issues COVID-19-related communications on a frequent basis. Nadcap stakeholders can find the entire “Nadcap Response to Covid-19” information in the PRI eAuditNet system under Resources > Documents > Public Documents > COVID-19: Nadcap Information. It includes:

  • Advice on safety measures to both Nadcap auditors and auditees during audits
  • Audit response deadlines and cumulative delinquency that can be waived with special circumstances
  • External service provider management and deviations to specification requirements tolerance
  • Guidance on quality-management-systems management and opportunities for accreditation length extensions
  • Recommendation on Nadcap accreditation length extensions, upon certain conditions

In addition, the two 2020 Nadcap meetings that were originally planned to take place in Beijing, China, and London have been successfully conducted virtually instead.

At the time of writing this article, the October Nadcap meeting in Pittsburgh, Pa., is still scheduled to take place face-to-face. However, all Nadcap symposia organized around the world have momentarily been postponed.