A Comprehensive Guide to Nadcap Heat-Treating Checklist AC7102
Understanding the Nadcap checklists is essential for performing thorough internal audits and maintaining overall conformance. This article will break down the requirements of AC7102, a critical checklist for heat-treating suppliers seeking Nadcap accreditation. The insights provided will help suppliers navigate the complexities of Nadcap audits and ensure compliance with stringent industry standards.
Overview of AC7102
AC7102 serves as the baseline checklist for all suppliers pursuing Nadcap accreditation in heat treating, regardless of the specific processes involved. It must be included in every audit, with additional checklists incorporated based on the supplier's scope of thermal processing. Throughout this series, we will explore the key elements of AC7102 and related checklists, providing guidance on how to address the most common non-conformance reports (NCRs) identified by the Performance Review Institute (PRI).
Understanding the Structure of AC7102
The AC7102 checklist is divided into 10 main sections, excluding job audits, which simplifies the process of identifying and meeting requirements. This structure helps suppliers ensure that all necessary areas are addressed during both internal and external audits. It's important to note that certain questions are marked with a (UXY) designation, indicating that these questions must be answered by all suppliers, even if the specific UXY designation does not directly apply to their operations.
Section 1: Nadcap Audit Requirements
The first section of AC7102 focuses on the Nadcap audit requirements, specifically the self-audit (or internal audit) that suppliers must complete before the official Nadcap audit. This section references the Nadcap Operating Procedure OP1105, which is available on the eaudit.net website within the documents section. It’s critical for suppliers to familiarize themselves with Nadcap operating procedures, as they apply universally to all suppliers seeking or maintaining accreditation.
The self-audit must include the Nadcap checklists relevant to the supplier’s current or prospective scope of accreditation, as stated in questions 1.1.1 and 3.5.2. Interestingly, paragraph 3.5.2, which essentially repeats the requirement in 1.1.1, ranks as No. 10 on the list of the top-10 findings for AC7102.
During the self-audit, suppliers are required to identify the procedure and paragraph number for each checklist question that necessitates it. For example, question 3.6.4 asks, “Are there procedures that address the use and placement of load thermocouples when required by specification or customer requirements?” This question uses the term "procedure," indicating that a specific procedure and paragraph must be referenced in the response. Similarly, questions that include phrases like “do documents exist…” signal that supporting documentation should be identified and referenced.
The self-audit is a critical tool for ensuring compliance, and having robust procedures and practices in place for conducting it is essential. When I perform internal audits for suppliers, I typically identify the relevant procedure, its revision, and the paragraph number for each question, even if the checklist does not explicitly require it. This practice serves multiple purposes: it provides clear references during the Nadcap audit if questions arise and it ensures that non-applicable topics are explicitly excluded from procedures. For instance, if titanium processing is not part of the scope, marking it as "N.A." without noting this in your internal procedures could lead to issues later on.
Key Questions from Section 1
Question 1.1.1.1: “Did the auditee perform a self-audit as above, including all applicable job audits?”
This question is No. 3 on the top-10 findings list for a reason—it addresses a common pitfall for suppliers. The self-audit must be completed thoroughly, with all job audits relevant to the supplier’s scope of accreditation included. For example, if your scope includes AC7102, AC7102/8, and AC7102/2, the latter being specific to aluminum heat treating, you must complete the two job audits listed at the end of AC7102/2. However, you do not need to complete all 10 job audits on the AC7102 baseline checklist; you can subtract the job audits included in the additional checklist.
This flexibility is often a point of confusion for suppliers, leading to questions about how many job audits need to be completed. Understanding this allows suppliers to accurately complete the self-audit without unnecessary redundancy.
Question 1.1.2: “Were all non-conformances identified by the auditee’s self-audit addressed by their corrective action system prior to this Nadcap audit?”
This question highlights the importance of addressing any non-conformances identified during the self-audit before the official Nadcap audit. If any checklist questions, including those from additional slash checklists, were marked “NO,” the supplier must ensure that these non-conformances are resolved through their corrective action system. In 2016, heat-treat auditor advisory HT-16-003 provided additional guidance on how to handle these situations, emphasizing the need for thorough follow-up and documentation.
Question 1.1.3: “Did the auditee provide the following documents to the auditor 30 days prior to the audit?”
Ranked as No. 2 on the top-10 findings, this question addresses the pre-audit submission of key documents to the auditor or via eaudit.net. The question lists six categories of required documents:
- List of equipment
- List of purchased services
- List of prime customers and specifications
- List of heat-treat specifications
- Copies of general internal procedures applicable to heat treating
- Copy of the organization chart
To streamline this process, I recommend that suppliers create a template that includes all these items. Having the list reviewed and verified by the quality team before submission ensures that nothing is overlooked, reducing the risk of non-conformance.
Quality System Requirements
Within the Quality System Requirements section of AC7102, one of the most critical questions is:
Question 3.4.1: “Are all corrective actions from the previous Nadcap audit still implemented?”
This question is pivotal for maintaining ongoing compliance. During the self-audit, suppliers must verify that all corrective actions from the previous Nadcap audit are still in place and effective. If a Nadcap auditor finds that previous corrective actions have not been implemented or maintained, the supplier will receive two major findings: one against the supplier’s quality system and another against the original finding. Moreover, a non-sustaining finding will negatively impact the supplier’s merit status, which can have significant implications for future audits and accreditation status.
Another important question in this section is:
Question 3.9.2: “Are consumable goods, such as process atmospheres, quenchants, salts, thermocouples, and materials for test samples, ordered and accepted according to an in-house document or to a specific standard?”
This question ties directly to Question 4.1.1, which requires suppliers to have documented procedures for receiving, inspecting, and releasing consumables. For example, when thermocouples are received, a shipping clerk might review the certification. However, there must be evidence of the clerk’s training, as specified in Question 4.1.1, to ensure they are qualified to perform this task. This practice ensures that all consumable goods meet the necessary standards before being used in the heat-treating process.
Key Personnel Requirements
The Personnel section of AC7102 includes two critical questions that are sometimes overlooked:
Question 4.1.1: “Are there training procedures that assure personnel performing contract review, job planning, heat treating, and associated quality and test functions are competent to perform assigned tasks?”
This question is often misunderstood as applying only to furnace operators, but it actually covers five categories of personnel involved in the heat-treating process. Each category must have documented training procedures to ensure that all individuals are competent in their roles, from contract review to final testing.
Question 4.2.2: “Do records indicate that the evaluations are performed at documented frequencies and the results reviewed with employees in a program of continuous improvement of personnel?”
The key part of this question is the emphasis on continuous improvement. Procedures should not only document the frequency of evaluations but also describe how the results are reviewed with employees to foster ongoing development and improvement. This ensures that the workforce remains skilled and up-to-date with the latest industry practices.
Process Control Testing
Process control testing is another area that can be challenging to navigate. The AC7102 checklist requires suppliers to account for all process control testing performed (excluding pyrometry), document the testing requirements, frequency, and expected results. This serves as a tracking tool and can be organized into a process control matrix or a control plan. Those with a background in quality engineering may recognize this as a "process control plan."
During a Nadcap audit, the auditor will typically request documentation for four different tests. These could include mechanical testing, hardness testing, furnace burnouts, or titanium (Alpha Case) testing. It's essential that this part of the checklist is thoroughly completed by your staff during the internal audit to ensure readiness for the official audit.
Furnace Control and Maintenance
Within the Furnace Control and Maintenance section, one particularly important question is:
Question 9.1.2.1: “Does the internal procedure specify the method for determining heat-up rate, start of soaking time, end of soaking time, and cooling rate?”
This question, which ranks as No. 6 on the top-10 findings, requires suppliers to clearly define these critical parameters within their internal procedures. The determination of the heat-up rate may either come from customer specifications or be defined as a default requirement in internal procedures. For example, a default requirement might state, “Unless otherwise specified, the ramp rate shall be 25-45 degrees Fahrenheit per minute.”
The start and end of soak are particularly critical and may be defined by applicable AMS/SAE specifications or customer requirements. Suppliers must have a clear procedure for determining when the soak period begins—typically when all furnace and load thermocouples have reached the specified temperature, including the minimum tolerance—and when it ends. This clarity ensures that the process is consistent and meets customer expectations.
Special Considerations for Vacuum Furnaces
The Vacuum Furnaces section of AC7102 includes a question that is crucial for suppliers using this type of equipment:
Question 11.2.1.2: “Calibration of vacuum instruments, flowmeters, dew point meter(s), and the related master gauges as appropriate.”
In my experience, the vacuum calibration portion of this question is often a common source of non-conformance. Since the revision of AMS2769, vacuum calibrations have become more controlled, and if a standard like GE’s P10TF3 applies to your operations, the requirements become even stricter. Suppliers must ensure that vacuum calibrations are performed according to the specifications that flow down to their operations to maintain conformance.
The Importance of Job Audits
Although job audits are not included in the 10 main sections of AC7102, they are critical components of the internal audit process. The job audit section typically includes one job audit, eight short jobs, and two long jobs. Short jobs involve a single temperature/treatment (such as annealing or aging), while long jobs involve a two-stage process (such as solution-age or austenitize-harden). It’s important to include all materials processed within these job audits to ensure comprehensive coverage.
One challenge I’ve encountered is when suppliers perform more focused thermal processing, such as a captive heat treater that only processes titanium. In such cases, the supplier may only have short jobs to offer, with no long jobs available. This situation should be discussed with the staff engineer before the internal audit to ensure compliance.
It’s also essential to consider jobs that are deemed export-controlled (EC). Throughout the job audit section, the designation “EC” indicates that if the job is export-controlled, no detailed information should be recorded in those fields—only the notation “EC.” The PRI monitors this closely, so it’s important to document job audits with care when export control applies.
Sections of AC7102/1: Furnace Brazing as a Heat-Treat Commodity
One of the initial challenges suppliers face is recognizing that furnace brazing, while technically a joining process, falls under the heat-treat commodity due to the use of a furnace. This distinction is crucial when structuring procedures for Nadcap qualification. For instance, a supplier might process both aluminum and furnace brazing—two distinct tasks requiring different furnaces. Since furnace brazing is included in the heat-treat commodity, it’s important to incorporate general brazing requirements into the overall heat-treat procedure. Understanding that AC7102 requirements apply to both furnace brazing and general heat treating will help you structure your procedures correctly.
AC7102/1 is divided into 13 sections, each capturing critical variables in the furnace brazing process. These requirements may be flowed down to suppliers through purchase orders, prints, or industry specifications like AWS C3.6M/C3.6. However, it’s important to note that not all requirements will be reflected in the AC7102/1 checklist. For example, AWS C3.6 mandates quarterly temperature uniformity surveys (TUS) for furnaces operating above 2,000°F. A supplier with a Class 3, Type B furnace must adhere to this quarterly frequency and cannot extend it to a semi-annual interval, despite what might be permitted in other standards. Such nuances must be considered when drafting internal procedures for furnace brazing and pyrometry.
Section 1: Validation
Section 1 focuses on Braze Process Specifications (BPS) and Braze Qualification Records (BQR). A BPS details the specific braze application and process parameters for particular part numbers, often tailored by suppliers to meet their needs. In contrast, a BQR qualifies the braze process itself, covering aspects like base metal, filler metal, joint type, and thermal cycle parameters. It also includes inspection techniques and metallurgical examinations. Question 2.1 in AC7102/1 addresses the importance of BQRs and any associated customer qualifications.
Section 2: Personnel
A common challenge in this section is Question 3.2.1, which asks, “Do procedures require periodic evaluation to ensure that approved personnel maintain proficiency in their assigned brazing filler metal application and related tasks?” This question aims to ensure that ongoing training occurs regularly to maintain personnel proficiency. Internal procedures should clearly specify the frequency of reoccurring training for those involved in braze application and furnace operations.
Section 4: Material Control
Section 4 deals with the control of braze filler metal, focusing on storage and mixing. A key question here is Question 4.4: “Is there objective evidence that the raw materials certifications are reviewed?” It’s one thing to have a procedure that mandates reviewing filler metal certifications, but consistently providing evidence of this practice can be challenging for some suppliers. It’s essential to receive and thoroughly review these certifications to confirm that the chemical composition and other purchase order requirements are met.
Section 6: Braze Equipment
This section covers the requirements for the braze furnace, typically a vacuum furnace, though it also includes requirements for dip salt brazing and atmosphere brazing. Questions 6.1.1 and 6.1.2 are often overlooked. These questions ask, “Is the gas dew point monitored?” and “Is the dew point monitored at the required location?” It’s important to note that these questions do not offer an option to mark “NA” and must be addressed. Procedures should specify how often the dew point is checked, the limitations (e.g., less than minus-60°F), and where the dew point sample is taken (e.g., as it enters the furnace, at the furnace point from the supply, etc.).
Section 7: Braze Filler Metal Application and Assembly Planning
Section 7 outlines the specific items required in the braze process planning documentation, such as routers, BPS and procedures. Question 7.7 asks, “Does the braze filler metal application/assembly work instruction/procedure contain the following, if required?” The following questions list the items that need to be documented. This is often where suppliers encounter gaps, so it’s crucial to ensure all required details are included in the planning documents.
Section 8: Braze Processing
This section builds on Section 7, focusing on what must be included in internal documents. Question 8.1.7 asks, “Instructions for determining when to start the brazing time and when to complete the brazing time?” The response to this question may depend on your internal heat-treat procedure, as this requirement is also included in AC7102. The start and end of soak times can vary based on the braze cycle. For example, some cycles specify a time range, such as “Braze for 6-10 minutes,” while others, like aluminum brazing, may require cooling once a thermocouple reaches a certain temperature.
Another important question is 8.1.16: “Instructions when to remove parts from the brazing equipment?” Although this question allows for an “NA” option, it’s relevant for materials like titanium or other sensitive alloys. If your procedures specify a temperature at which parts should be removed from the brazing furnace, the furnace recording must reflect this, and recording should not stop until the specified temperature is reached. In such cases, the furnace recording system must be calibrated to the designated temperature.
Section 9: Post-Braze Cleaning
Post-braze cleaning methods can vary depending on the brazing process used. For suppliers using stop-off, cleaning procedures will differ from those who do not. Question 9.1.1 asks, “Does the post-brazing cleaning work instruction contain the following, if required: Method and product used for post-cleaning?” This question does not provide an “NA” option (unless the entire section is marked “NA”), so it’s essential to document a cleaning method.
Section 13: Brazing Rework
Brazing rework is often necessary to correct non-conforming aspects of a braze joint. Question 13.1 asks, “Where required, are the total rework cycles or the total time tracked and recorded to verify that the maximum time at temperature, or the maximum number of cycles, meet the requirements of the engineering drawing or specification?” Tracking braze rework cycles can be challenging, but a practical approach is to route defective parts through your non-conforming material system, where they will undergo material review and have rework assigned accordingly.
Sections of AC7102/2: Aluminum Heat-Treat
Aluminum heat treating is a specialized process that requires precise control and careful adherence to standards. Heat treatable aluminum alloys, which contain magnesium, are known for their strength and ductility. Magnesium not only enhances strength but also provides corrosion resistance. The successful heat treatment of aluminum hinges on the dissolution of Mg2Si, typically achieved at temperatures 10-15°F below the eutectic point. This sensitivity necessitates the use of Class 2 furnaces (±10°F) per AMS2750. Failing to maintain this temperature uniformity can lead to incipient melting at the grain boundaries, rendering the aluminum irreparable and necessitating its scrapping. Given the sensitivity and widespread application of aluminum heat treating, Nadcap has developed a separate checklist: AC7102/2.
AC7102/2 consists of 13 sections, each addressing different aspects of the aluminum heat-treating process. The checklist incorporates several industry and prime specifications relevant to aluminum heat treating, as the PRI Heat Treating Task Group has included these general requirements in AC7102/2.
Since section 3 (salt baths), section 6 (spray quench/forced air quench), section 9 (water/polymer quenchant used in conjunction with salt baths) and section 11 (handling fasteners) have limited uses for our purposes today, we will be skipping these sections.
Section 1 — Facilities
Section 1 focuses on the furnace class and instrumentation type required for thermal processing equipment. These requirements are typically specified in the industry or prime specifications provided to suppliers via purchase orders or prints. For example, if AMS2770 is specified for a solution heat treatment, the furnace used must comply with Class 2 standards as outlined in AMS2750. This requirement is directly linked to the critical temperature uniformity needed to prevent incipient melting.
Section 2 — Control of Heating Environment Above 400°F
Section 2 addresses the control of products of combustion entering the furnace and the use of protective compounds. It’s important to note that each question in this section includes the phrase “…when required by specification…” or “…when required….” This means that if you’re processing in an environment above 400°F, these questions must be considered, even if all are marked N/A because they don’t apply. For example, AMS2770 might not require these controls, but AMS2771 might, making it essential to evaluate which specifications apply to your process.
Section 4 — Racks, Fixtures, and Baskets
Question 5.1 in this section parallels AC7102’s question 9.14.1, requiring that when shop paperwork specifies the use of a specifically designed rack, the tooling must be identifiable and used accordingly.
Question 5.2 focuses on preventing entrapped water within the fixture or rack from entering the furnace. This is particularly relevant to aluminum solution heat-treating furnaces where parts are quenched directly in water. Operators must check for entrapped water to ensure it does not enter the furnace after quenching.
Question 5.3 requires that procedures include a statement regarding part spacing. Both AMS2770 and AMS2771 specify that spacing must allow for free flow of quench and air. Prime specifications like BAC5602 may have even more detailed requirements. Proper spacing is crucial during aluminum solution heat treating, as it affects the quench process, which has three stages: vapor, boiling and convection. Ensuring proper agitation during these stages is essential to achieving the desired heat transfer and minimizing distortion.
Section 5 — Quench Systems
Section 5 focuses entirely on quench delay, defined as the time from when the furnace doors open to when the parts are fully submerged in the quench solution. This delay must be specified in your work instructions and verified during each quench cycle. There are systems available to measure quench delay automatically, but it can also be tracked manually using a stopwatch. Logging the quench delay for each cycle is critical, as it is a key process parameter that must be controlled.
Section 7 — Quench Control
In addition to the three stages of the quench process, this section emphasizes the importance of temperature and agitation. If the quench solution needs to be heated to minimize distortion and prevent cracking, the temperature requirements must be clearly indicated in your work instructions. The quench solution must reach the required temperature (or range) before the parts are immersed.
Section 8 — Water/Polymer Quenchant Solutions
This section is relevant only to suppliers using a water/polymer mix for quenching. If you use only water, this section should be marked N/A. For those using water/polymer solutions, it’s necessary to certify the solution in accordance with AMS3025. Each batch must have a certificate on file, and there should be evidence of review and approval. Additionally, the concentration of the solution must be checked at specified intervals. If a refractometer is used for this purpose, it must be calibrated regularly.
Section 10 — Refrigeration When Required by Specification
Not all suppliers use refrigeration to retain tempers, but those that do must have clear instructions regarding time and temperature, including how the refrigeration cycle is recorded. The control and recording system must also be calibrated, and a System Accuracy Test (SAT) performed on the refrigeration unit.
Section 12 — Aluminum Solution Heat Treating Furnaces with the Heat Source in Walls
This section has two important parts. The first question requires that the heat source does not have a direct line of sight to the parts being processed. The second involves radiation survey testing. In my consulting experience, suppliers often struggle to provide evidence of a radiation survey, even though it was likely performed at some point. The radiation survey is a one-time test detailed in AMS2750, and it must be repeated if the radiation characteristics change.
Section 13 — Periodic Testing
Periodic testing requirements typically flow down from industry or prime specifications. If these requirements apply to your facility, you must document the frequency of these tests and retain evidence that the testing was performed as required.
Sections of AC7102/5: Hardness & Conductivity Testing
Hardness and conductivity testing are essential processes for validating specific heat treatments. Depending on the material and the heat treatment involved, different types of tests are used to ensure the required results are achieved. While Nadcap does not provide a top-10 list of findings associated with hardness testing, there are several common challenges that suppliers often encounter. In this section, we will explore the critical aspects of AC7102/5, the Nadcap checklist for hardness and conductivity testing and discuss how to navigate these challenges effectively.
AC7102/5 is organized into 13 sections, each addressing different aspects of hardness and conductivity testing. This checklist incorporates several industry and prime specifications relevant to these tests.
That said, we are going to be skipping over section 5 (material identification and control), section 6 (alternative methods) and section 12 (Vickers hardness testing), as these sections don’t present significant challenges.
Section 1: Written Procedures
Section 1 of AC7102/5 is similar to other checklists in that it outlines the minimum documentation requirements for internal procedures. One common challenge is the omission of specific items, such as the number of tests or impressions needed for each reported value. For example, if three impressions are taken and averaged, this process should be clearly documented in the procedures. If a single test or impression equates to one reported value, this should also be specified. Another frequent omission is the location for performing testing. Suppliers often include default language in their procedures, referencing travelers or work instructions for specific areas based on purchase orders or prints.
Section 2: Personnel and Training
Qualification of hardness-testing personnel is crucial and should be specific to the testing processes used by the supplier. A common issue is the general approach to training, where operators are taught procedures for tests that are not performed at the facility. This section requires that hardness test operators receive training, per industry standards, on verification testing and part testing. Training should include representative geometries of parts, such as round or flat specimens, depending on what is tested. Operator qualification typically involves a written test covering procedural requirements and a practical test where the trainee performs both verification and part testing under supervision. Requalification should occur at defined intervals, such as when an operator has not used the machine for more than six months or if their competency is in question.
Section 3: Facilities, Equipment, and Maintenance
The key challenge in this section is ensuring maintenance is properly documented. ASTM E-18 requires regular maintenance, typically noted on the indirect verification certification. When issuing a purchase order to an external service provider for indirect verification, suppliers should request that maintenance is included. Internal procedures should also specify that maintenance is performed during indirect verification and that it must be confirmed on the certification upon completion.
Section 4: Calibration
One of the most challenging aspects of this section is compliance with the direct verification requirement outlined in paragraph 3.2.4.1. In October 2018, a Nadcap HT Auditor Advisory (HT 18-009) stated that all testing machines must have evidence of direct verification, which is typically performed by the manufacturer when the machine is new or after major repairs. Some suppliers may no longer have this evidence if the machine is old, but compliance is mandatory. If necessary, the machine must be sent back to the manufacturer for direct verification.
Section 7: Hardness Conversion
When using hardness conversions, this section mandates the use of ASTM E-140 for the conversion process. Both the measured value and the converted value must be reported, ensuring transparency and accuracy in the testing process.
Section 8: Hardness Test Reports
A common challenge in this section is the requirement in paragraph 3.6.4, which often lacks a designated place for operators to log specific information. This could be documented in the daily verification report or the hardness testing log, depending on the supplier's practices.
Section 9: Hardness Periodic (Indirect and Daily) Verification
Section 9 outlines the requirements for both indirect (typically annual) and daily verification. ASTM E-18 provides detailed guidance on Rockwell hardness testing, which is more extensive than the checklist itself. Two common challenges in this section include indenter qualification and referencing the correct ASTM E-18 revision. When reviewing an indirect verification certification, suppliers should ensure that all indenters available for use are listed and that records are kept when indenters are removed or replaced. Additionally, the certification should reflect the correct ASTM E-18 revision applicable at the time of calibration.
Section 10: Brinell Hardness Testing
The Brinell hardness testing section mirrors the hardness testing section but includes specific requirements, such as sample thickness and major load cycle time. The most common challenge here is ensuring the load is applied for 10 to 15 seconds, as required.
Section 11: Rockwell Hardness Testing
Rockwell hardness testing is perhaps the most widely used section of AC7102/5. This section covers verification testing requirements and manual control, with several common challenges. Direct verification, as discussed in Section 9, is crucial, and suppliers must have evidence of compliance with ASTM E-18 to avoid findings during an audit.
Frequent issues arise with the following paragraphs:
- 3.9.2.2 - Asks if center-to-center spacing on test blocks is in accordance with the applicable specification (usually ASTM E-18). To mitigate spacing violations, internal procedures should clearly outline the spacing requirements, and suppliers may consider using test blocks with grid lines or marking indentations with a Sharpie-type pen.
- 3.9.2.8 - Asks whether the hardness testing operator verifies the anvil/fixture to ensure there is no damage before testing. Operators may forget to perform this examination, leading to non-conformance.
It’s also important to clarify that inspecting the indenter prior to testing is not an ASTM E-18 or Nadcap requirement but is required by Boeing. If you follow Boeing specifications, this inspection is mandatory. For other specifications, while it’s not required, inspecting the diamond indenter with magnification before daily verification testing is a good practice that can prevent issues.
Section 13: Conductivity Testing
This section covers conductivity testing for aluminum, with common challenges including properly stating the oscillator frequency in procedures and records. This frequency should be verified during calibration and at the time of purchase. Another challenge is adhering to the calibration frequency, which may be more stringent for different prime customers than the manufacturer’s recommendations. It’s important to fully understand customer requirements to ensure compliance.
Sections of AC7102/8: Pyrometry
AC7102/8 is one of the most critical—and often most challenging—checklists for suppliers undergoing a heat-treat audit. Pyrometry, which involves testing thermal-processing equipment to ensure uniformity and accuracy, is essential for achieving consistent and satisfactory results in heat-treated materials. The stakes are high; any deviation in uniformity or accuracy can lead to non-conforming products, resulting in costly rework or scrap. In this section, we’ll explore the key sections of AC7102/8 and discuss the most common challenges suppliers face, using examples to illustrate the importance of pyrometry in maintaining compliance.
AC7102/8 is divided into eight sections, each addressing different aspects of pyrometry. This article will focus on the sections that typically pose the greatest challenges to suppliers. We will also highlight the top-10 findings related to AC7102/8 as published by the Performance Review Institute (PRI) in 2019, which, although based on the previous version (AMS2750E), remain relevant under the current AMS2750F standard.
Section 1: General Requirements
One of the most significant updates in this section is the requirement that any third-party service provider performing pyrometry must be ISO/IEC 17025 accredited for the specific tests they conduct. For instance, if a service provider is hired to perform temperature uniformity surveys (TUS) and instrument calibrations, their accreditation must explicitly cover these activities and reference AMS2750.
Another key point is Question 2.3, which ranks sixth on the top-10 findings for pyrometry. This question pertains to the review of all pyrometry-related tests and calibrations, including thermocouple certifications, SAT and TUS reports, and instrument calibrations. Even if a third party conducts these tests, the supplier must have a system in place to review the results thoroughly and ensure they conform to AMS2750F.
Section 2: Temperature Sensors
A common issue in this section relates to Question 3.3. For example, a supplier might use a nonexpendable Type N thermocouple as an SAT sensor (nonresident), inserting it into various pieces of equipment, including quench tanks. However, if the thermocouple’s calibration starts at 100°F, it wouldn’t cover the lower temperatures of the quench tank, leading to potential non-conformance.
Question 3.7 has long been a challenge, particularly regarding the depth of insertion for Type E and K thermocouples used above 500°F. Suppliers must clearly state this requirement in their internal procedures and implement a control method at the furnace, such as mechanical means, to ensure compliance. The rule is that thermocouples exposed to heat in the work zone must remain in position, or more of the thermocouple may be inserted—retraction is not allowed.
Suppliers often ask how frequently furnace thermocouples (e.g., control, overtemperature) should be replaced. Under AMS2750F, the supplier must determine a replacement frequency, supported by data from SAT, TUS or instrument calibration. Note that prime and industry specifications may impose stricter frequencies. If a SAT waiver is in place, a specific control thermocouple replacement frequency is required.
A new requirement, Question 3.14, addresses how hot junctions are made. The hot junction, where dissimilar wires touch to generate a millivolt signal converted to temperature, can be created by twisting, welding, or both, as long as no filler metal is used.
Section 3: Instrumentation
Question 4.2.3 mandates that each thermocouple type and input/output being used must be calibrated. It’s not uncommon to find a type or input/output uncalibrated when reviewing certifications, so suppliers must be diligent in ensuring all necessary calibrations are performed.
Questions 4.2.4 (test instruments) and 4.3.2.4 (furnace instruments) can sometimes cause confusion. These questions require calibration of each channel, either individually or as a group, depending on the equipment’s design. For example, a Yokogawa DX model recorder might calibrate multiple channels simultaneously, while other models may require individual calibration. It’s up to the supplier to consult the manual and calibrate accordingly.
Calibration of sensor systems that qualify instrumentation types is critical, as highlighted in Question 4.3.2. For example, in Type D instrumentation, where a load thermocouple is occasionally used, both the main sensor system and the load thermocouple system must be calibrated, as they contribute to product acceptance.
Question 4.3.3 has been updated to reflect a change in AMS2750F: Sensitivity testing is now required only for analog instruments, not digital ones.
The top finding related to AC7102/8, as per PRI, involves stickers and calibration records, which is addressed in Questions 4.3.4 through 4.3.4.5 and 4.3.5.1 through 4.3.5.19. To ensure compliance, suppliers should document these requirements in their internal procedures and include them in quality verification processes.
Section 4: System Accuracy Testing
Question 5.3.3 requires that System Accuracy Tests (SATs) be performed consistently each time. The position and depth of the test thermocouple must match the initial SAT setup, which should be documented in internal procedures to avoid errors during testing.
Another common issue involves Question 5.3.5, which requires SATs on sensor systems that qualify the equipment’s instrumentation type and any additional systems used for product acceptance. For example, if a supplier designates equipment as Type D but occasionally uses load thermocouples for product acceptance, those thermocouples must undergo SATs as well.
Question 5.3.5.3 addresses additional systems used to justify SAT interval extensions. For instance, if two Type N thermocouples are installed—one for control and one for overtemperature—the overtemperature thermocouple would require an SAT if it’s used to justify the extension.
Question 5.5 covers the alternate SAT requirements, which some suppliers initially found confusing. By now, most suppliers understand the documentation requirements for alternate SATs. However, it’s crucial to recognize the new documentation standards and ensure all required details are properly recorded.
Section 5: Temperature Uniformity Surveys
One of the initial challenges under AMS2750F is the extended TUS frequency. Tables 18 and 19 in AMS2750F specify the number of successful TUSs needed before extending the interval. For example, a supplier with Class 2 Type D equipment must perform TUSs monthly for four consecutive successful tests before extending to bimonthly. Under AMS2750E, the initial survey counted as one of the four required tests, but this is no longer the case in AMS2750F.
Another issue arises with Question 6.1.5, which requires that vacuum furnaces using partial pressure perform one periodic TUS annually with partial pressure in the range used, involving one of the partial pressure gasses. Although this is a new requirement, some suppliers have missed it during audits.
Question 6.2.5 requires suppliers to maintain a detailed diagram showing the location of furnace and test thermocouples. It’s common to find diagrams that either omit the control thermocouple’s location or incorrectly identify it. Accurate documentation of thermocouple locations on the TUS certification and internal procedures is essential.
Reach Out To Conrad Kacsik Today
Pyrometry is undoubtedly one of the most challenging aspects of a heat-treat audit. The key to mastering pyrometry lies in continuous training and hands-on practice. Numerous training programs are available to support suppliers in this endeavor.
If you’re interested in learning more about how Conrad Kacsik can help you remain compliant and competitive for pyrometry audits and more, reach out to contact us today.
