Attendance at the October 2013 Nadcap meeting was better than most years, but it still yielded fewer heat treaters than there ought to have been. That said, in this article we’ll take a look at the arrival of new specification AMS 2750 Rev. E and some of the changes.
One of the most interesting sessions at Nadcap this year focused on the top-10 nonconformances. Unsurprisingly, eight out of the 10 were regarding pyrometry. Much to the annoyance of quality managers, the devious specification behind countless occurrences of heartburn is still AMS 2750. It seems the industry’s attempt at clarifying the requirements for aerospace primes has, as a side effect, created new fodder for the auditors to reflect on.
Developed by a contingent of industry representatives and prime manufacturers belonging to the AMEC (Aerospace Metals Engineering Committee), this specification seeks to be the standard for pyrometry. The primes’ new approach is to accept AMS 2750 and then select certain paragraphs or clauses that are in disagreement with their specifications and give an option to accept AMS 2750 with a few exceptions. The latest prime to take up this method is Boeing’s Commercial Division with its latest PSD released for BAC 5621k.
Compared to the rest of industry pyrometry specifications, AMS 2750E does do a lot of things right. An important one is organization. The specification is laid out with all tables in the back and few, if any, figures littering the specification. It starts out with the ominous warning, “Changes are extensive and not marked.” To this, I would also add to not forget the free pyrometry guide from Nadcap, which is updated at least twice a year and sometimes more often. This guide serves to explain paragraphs that are confusing or need more detail. Though it does not create requirements, a company can be written up for “clarifications” to existing requirements contained within the guide.
There is a greater focus on standardizing vocabulary. Definitions have been moved from the back to the front for greater emphasis, and several get an update. A few notable ones are Deviation, Digital Instrument, Stabilization and the need for Delegation of Quality Approval. Standardizing all the vocabulary in procedures, vendors and labels used in your facility is incredibly important to avoid needless issues. Delegation for quality approval is an interesting add-in and addresses the concern primes have with documented approval for signing off items on the shop floor. At this juncture, it isn’t enough to be trained in the specification. You need to have a clear link of approval from the quality department to the shop floor for things like chart sign-offs.
Going from AMS 2750C to Rev. D was an absolute roller coaster in this section, but the new revision doesn’t ruffle too many thermocouple feathers. The major changes include clarifying and extending the use of load thermocouples in the 1801-2199°F range to 90 days or 90 uses.
Vacuum heat treaters will now need to take a second look at the policies to see how this relaxes some of the requirements. AMS 2750D was also silent on the replacement for process thermocouples. The new requirement insists on a written schedule that must be based on supporting data such as SAT, TUS and recalibration data. So, gone is that thermocouple that has been in the quench tank for years. Put a limit on the life, which also means you now must very accurately track its installment date. One warning in the specification reads, “Compliance with these intervals does not relieve the user of the responsibility for ensuring that excessive drift has not occurred.” So, failing an SAT really shouldn’t be the time to change thermocouples. Lastly, a fantastic graphic has been added AMS to 2750E (Figure 1) to clarify when to calibrate and what kind of thermocouple to use and for how long.
There are two very important changes to this section. The requirements for test instruments were totally absent from AMS 2750D and are now given some guidelines. The number of test points need to be at a minimum of six within the range used for each channel and must adhere to the requirements of Table 3 and the associated notes.
Previously, there was a requirement to calibrate the exact midpoint of a range, which has now been revised to necessitate picking a point in the middle third of the range. This should ease the needless findings this paragraph produced.
Perhaps the most important change is to the breakout of the paragraph that requires an SAT. Relating to process instruments, if an instrument is checked and adjusted, it must be followed by an SAT. Heat-treatment shops using outside vendors will need to take notice to see if this is included on reports.
System Accuracy Testing (SAT)
One of the most confusing topics for heat treaters is that of the SAT requirement. It creates a perceived burden on maintenance staff, delays production and is likely the source of many errors in calculation. The new revision re-attempts to give this section a lift with new examples and different scenarios from start to finish. The new charts are helpful, but like anything, training is key.
The major change occurred in the Alternate SAT section and is currently referenced in the workshop section of eauditnet.com. Alternate SATs must be done at the calibration points, not just a single point, and should anything change from a calibration or correction-factor standpoint, the previous two months need to be revalidated.
Temperature Uniformity Surveys (TUS)
The section on TUSs has been modified only modestly with the main change coming to the requirement of test points for periodic surveys. If you are in a single class greater than 600°F, you must pick a point to survey within 300°F of BOTH the top and bottom of the qualified range. For example, if you are a heat treater with a vacuum furnace that has class-2 and class-5 ranges, this may trigger a four-or-more-point survey certain times of the year, depending on when and how the temperatures are picked. Heat treaters are advised to revise and settle on monthly points to make sure all points are covered.
The requirement for rounding has been handed down in all sections, and heat treaters should be alerted to understand that not all software (such as Microsoft Excel) automatically meets the requirements. ASTM E-29 was just revised this year and goes into considerable detail on this subject. All procedures should be reviewed and personnel trained extensively to assure conformance.
The specification is confusing, and the first recommendation is to get help from consulting companies, PRI or personnel who have extensive knowledge on the application of pyrometry. If there is ever a doubt on procedure, detail it in writing and send it off to the respective prime for approval. Furthermore, as technology for controlling furnaces gets better and better, expect the specification to get tighter in its requirements and traceability. There is a general lack of investment on training within the heat-treatment industry. Unfortunately, we just do not have the influx of graduates in our field to pass on valuable on-the-job skills. The absolute most-important institution in your companies is the ability to internally audit the training and existing procedures, but that’s an article for another day. IH
For more information:Contact Adeel Karim, president, Doctor Furnace, Inc., 508 West Fletcher Ave. Suite 103, Tampa, FL 33612; tel: 352-315-9190; fax: 352-350-1520; e-mail: email@example.com; web: www.doctorfurnace.com