Andrew Bassett, President, Aerospace Testing and Pyrometry
A pyrometry compliance company in the heat treat industry recently reported the successful launch of a program to bring 12 of 38 heat treating furnaces up to pyrometry compliance standards for a large manufacturer with a focus in the aerospace industry located on the West Coast. Aerospace Testing & Pyrometry (ATP), an Easton, Pennsylvania-based pyrometry compliance company, reported earlier this week on LinkedIn that their West Coast Division had started assessing the heat treat furnaces for this large manufacturer with a focus in the aerospace industry.
ATP personnel involved in the project included Ivan Mayorga, John Hollman, and Anthony Gomez.
ATP did not disclose the name of the aerospace manufacture for whom they were doing work nor did they comment on the status of the other 26 furnaces not being serviced by ATP.
To see the LinkedIn post from which this press release was taken, click here.
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
Andrew Bassett President Aerospace Testing and Pyrometry Source: Aerospace Testing and Pyrometry
A large aluminum producer in the U.S. Midwest received assistance from a North American pyrometry service provider to ensure their heat treat and laboratory furnaces were ready to run.
After the visit from the pyrometry service provider, Aerospace Testing & Pyrometry, Inc. (ATP), four laboratory furnaces were certified and three of four heat treat furnaces were wired and ready to go. One 40 point survey, two 35 point survey and one 25 point survey on a forty foot tall drop bottom furnace.
"We love our Pyrometry Services," commented Andrew Bassett, president of ATP. "All the certifications will be run through our newest venture, Aerospace Compliance Software."
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
Heat Treat Radio host Doug Glenn continues his conversation with AMS2750F expert Andrew Bassett. This time the pair discusses Revision F changes to System Accuracy Tests (SATs).
Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript.
The following transcript has been edited for your reading enjoyment.
DG: We are back today for our second episode of a three-part series with Andrew Bassett. Andrew is the president and CEO of Aerospace Testing and Pyrometry, headquartered out of Bethlehem, PA, with offices across the county. They do a lot in pyrometry services and related things. Andrew also had a seat on the committee that was responsible for – that owned – the AMS2750 revision F, so he can speak with firsthand knowledge of some of these changes.
If you are interested, you can listen to the first part, which dealt with the major changes in thermocouples and sensors, major changes in instruments, major changes in calibration, and then we also spent a little bit of time right at the end of the last episode talking about offsets.
AB: Yes, and the offsets were one of major changes that we, as a team, did a very good job of spelling out the new requirements for the two different offsets: modification offsets and correction offsets. So that’s a valuable tool to go back and take a look at.
Episode 1 of 3 of AMS2750 series
DG: If you didn’t catch that first episode, you can certainly do that. You can go to www.heattreattoday.com, jump back into the radio section which is under heat treat media on our main navigation tab, and check that out. It would be very worthwhile.
Before we jump into the topic for today, which is the system accuracy tests (SATs), I wanted to ask you a question about this revision. Often, the AMS folks will come out with a minor modification, or not a huge modification, let’s say; other times, it’s pretty much a re-write, end to end. How would you classify this revision F? Where does it fall on that scale?
AB: It leans towards the side of a complete re-write. I think one of the big things that changed was obviously the number of pages of the document; it jumped from roughly 43 pages up to 54 pages. We expanded the number of tables that were from revision E, which had 11 tables, into 25. This was to do some more clarifications of the requirements, or to spell things out a little bit more. I would be leaning on the side of this as being more of a complete re-write. There’s going to be quite a bit in there that is the same old stuff from the previous revisions, but there is quite a bunch of new stuff.
I would lean towards saying that this was a complete re-write and that’s why there were no change bars associated with the spec. Typically, when these specs get revised, the change bars show you where the changes are, but since this was more of a re-write, we left out the change bars this time around.
DG: Instead of having someone go in and “cheat” and just look at the change bars, you’ve got to pretty much start from the beginning and go straight through.
Where do you see some of the major changes in rev F on the overall or the resident SAT?
(source: Andrew Bassett, ATP)
AB: Not a whole lot completely changed on the resident sensors. We still allowed for the same sensors as we did in the previous revisions, where you are limited to different types of sensors based on the temperature ranges, that they were going to be seeing. For instance, if you’re above 500 degrees Fahrenheit, then you’re going to be limited to type N, S, R or B thermocouples, and if you’re above 1,000 degrees, they would have to be what’s called a nonexpendable thermocouple, the metal sheathed type thermocouples. We left that stuff alone. But one of the things we did allow for with the new resident sensors, which I believe is a benefit to the supplies that are using the resident sensors, is that we’re going to allow for some things. Let’s say you have an over temperature sensor, and you also want to use that as your resident sensor. Now you’re allowed to do that as long as you follow the guidelines that say a resident sensor has to be replaced. If it’s a base metal thermocouple it has to be replaced every 90 days, or on a quarterly basis. If it is a noble metal, one of the type R, S, or Bs, it would have to be replaced or recalibrated every six months. We did allow for cases where you have an extra sensor that is being used in dual roles (that is, a resident sensor that also functions as a high limit protection), then you can go ahead and do that. I think that that is something that is beneficial to the suppliers, in that we don’t have to go out and put a third sensor into a furnace or drill a hole to put our resident sensor in.
The one thing that we really want to emphasize with these resident sensors is that their position is to be verified during the installation process and when it’s replaced. When a resident sensor is in a fixed position, we want to make sure it is not moving. Typically, you see a compression fitting that is going to tie the thermocouple down and lock it into place. We want to make sure it is not moving between tests. So, now when you replace these things, you must verify the positioning when you put it in on a replacement basis.
Also, it’s always been the requirement to put the thermocouple in for the 90 days or 180 days, and leave it in there. We’re going to allow you to take it out between the tests, but only as long as it is verified after every single time it’s replaced. I’m not a big believer in that; just because someone from Quality doesn’t come out and verify it doesn’t mean that it could be in the wrong position. But we are allowing you to independently move this thing in and out between the test if you want; that is acceptable. You still have the same replacement periods as quarterly and 180 days depending on the sensor type. We did give a little leeway on that from the resident sensor standpoint. Again, we didn’t make a whole lot of changes on it. We just wanted to spell out the little bit of differences allowing for other types of sensors to be used, or have a dual purpose, I should say.
DG: Let’s move on to the second issue, and that is the alternate SAT process, which I know has sparked a lot of questions with the articles we’ve had on our website. We’ve always had people asking about what they can do, what they can’t do. Let’s talk about that.
AB: Sure. The previous revision in rev E was kind of this dark black hole of what the alternate SAT process was all about. Finally, it was more spelled out in what’s called the “PyrometryReference Guide.” That’s the document that NADCAP puts out, the “pyrometry for dummies,” so to speak. This is basically their interpretation of AMS2750. And then kind of evolved that into what’s called a “heat treat audit advisory.” There were different interpretations of this alternate SAT which were too conflicting to the suppliers. We said, “Let’s make it more clear-cut of what the expectation of this alternate SAT process is.”
First off, the process applies to load sensors that are used once, or for any other type of sensor control or recording sensors that are replaced at the same, or less frequent than the normal, SAT intervals. One of the things that was in the previous version, which we kept, is that the calibration must be performed from where you connect the sensor. Then, once you do that calibration, one of the following three options have to be met. Option 1 is that we take the sum of the sensor calibration error. That’s when you first complete calibration from the point of connection and run through the whole system, including the connections, the lead wire, and the instruments. Then, you document those results and algebraically add that to the correction factors or the errors of the wire either being used or replaced more frequently, and if the sum of those two correction factors are within the allowable SAT tolerance of AMS2750, you would have to document that. And that’s the first option; it’s basically a math function; it’s sitting at your desk and taking the calibration report of your process instrumentation, typically from the recording, and adding it to the wire that’s being used. If you fall within that certain table of AMS2750 for SAT tolerances, you’re good to go. It’s kind of a “desk SAT,” as they call it.
The other way of doing this is to use the appropriate sensor and instrument calibration correction factors. You can either program them into the system or apply it manually as allowed by the limits in AMS2750. Basically, you’re taking the correction factors for the instrumentation that you have calibrated and the sensors that you have calibration “certs” on, and programming that into your system. Again, as long as that meets within the applicable table of AMS2750, that is the second option that is allowed. Because you’re basically using the correction values from the calibration reports for your instruments and your thermocouples, you will always be within your SAT requirements.
The third option allows you to do a couple of things. For one, you can limit your instrumentation calibration error. A company comes in and does your calibrations, and the supplier says they don’t want any of their channels to be more than one degree out of calibration, so, you adjust the instrument calibration to be within that limit. Or, you can specify when you purchase thermocouples wire that you won’t take any thermocouple wire that is no more than two degrees out throughout the whole range you need them calibrated. In that instance, you will always be compliant to the requirements of the SAT tolerances. So, if you restrict the calibrations and you restrict the error on the thermocouples, then you will always meet that requirement. All you would have to do is show, for documentation purposes, the instrument calibration reports that say it is all within 1 degree and all of the wire certifications are within two degrees, and that will always meet the most stringent requirement for SAT tolerances. As long as that documentation is there, you will be able to show compliance to the requirement.
[blockquote author=”Andrew Bassett” style=”2″]“Before, there was no requirement of how to document all this, so we actually put in some hard requirements down on how to document the alternate SAT requirements.”[/blockquote]
Those are the more defined options you have. Before, if you gave it to 100 different people to read, and they said, “I don’t know what to do with this information.” Well, now we’ve put out what we actually meant and defined it a little further now.
DG: Great, so that covers the first two that we wanted to talk about – the overall of the resident SAT and now the alternate SAT – so let’s wrap up with this SAT waiver, which is obviously of interest.
AB: First, I want to jump back real quick into the alternate SAT. We finally added some documentation requirements. Before, there was no requirement of how to document all this, so we actually put in some hard requirements down on how to document the alternate SAT requirements. You have to list out the thermal processing equipment (you have to identify which furnace you’re doing this on), what is the sensor system that’s being tested, and what sensor or roll of wire that’s being replaced. You also have to identify the reason why you’re doing the SAT; for example, because you replaced the thermocouple after every run, something simple like that. If you’re doing the full calculation method, then you’d have to show all your calculated methods. We did finally put some teeth in to help you document this well.
DG: Now, the SAT waiver. Tell us about it.
AB: In all my years out in the field of pyrometry, I rarely found many suppliers that did this SAT waiver correctly. We didn’t change a lot of the basics of the requirements, but we did change some new requirements regarding how to gather your data to make sure that you do this correctly. We still require that if you’re using noble metal load thermocouples, which are the platinum based thermocouples, you replace and recalibrate them on a quarterly basis. If you have base metal load thermocouples, if they are expendable, they should still be just a single use. If they’re nonexpendable, sheath type thermocouples, they shall meet the requirements of Table 6 in AMS2750F, and that gives you guidelines of how often those need to be replaced.
If you have any kind of observations that are made and recorded on at least a weekly basis and which reveal any unexplainable difference between observable readings and readings of two recording sensors, this is where the change really occurred on those two additional sensors. We spelled out that these weekly readings have to be conducted at one production setpoint and measured within the five minutes at the end of the production soak period. What this weekly log is supposed to be doing is to compare one sensor against another sensor that you’ve identified.
Some people have used the control sensor as the one sensor and, let’s say, the high limit thermocouple as the second sensor. These have to stay within a two-degree relationship from the last successful survey, and so people were wondering when they were to take the weekly reading. We decided to spell this out a little bit further: this weekly reading must be done at production setpoint and measured within the minutes of the production soak period. In other words, you can let your thermocouples soak out for a period of time, during which you can complete your comparison check. These have to be within two degrees of the relationship determined at the most recent TUS temperature and at the nearest temperature tested during the most recent TUS.
For example, let’s say we do a survey at 1600 degrees and the control is reading 1600 degrees and my over temp is reading 1602. Next week, we come along and we’re running a job here at 1500 degrees and my control is reading 1500 degrees and my over temp is reading 1501, you’re good. You’re within that two-degree relationship. That’s where this two-degree relationship needs to occur.
But the one thing that we’ve done now is we’ve asserted that the two sensors have to be different types. Before, you’d have, let say, two type S thermocouples in your furnace; you can’t have two type S thermocouples now. You have to make a different thermocouple type for the relationship. This is more to catch any drifting of your thermocouples over time. For instance, if you had a type S thermocouple in your furnace as your control, you’re going to have to be limited to either a type B or type N thermocouple as that secondary sensor that you’re doing your relationship check with.
That’s what a big change is. Before people just used the two same sensors. What we were concerned about is – and let’s say those two thermocouples were made from the same lot of material – that there is a good chance that when the thermocouples start to drift, they’re going to drift in the same direction.
Again, we did put some similar restrictions on resident thermocouples. For the example I used, if you had type S control thermocouple, you’d be limited to type B or N, but we also allow for R as that extra thermocouple. But R and S are very similar in the chemical composition makeup, so we don’t allow an S to go against an R and vice versa, in that case. If you had a control thermocouple that was K, then really any other thermocouple that is allowed once you’re above 500 degrees you’re limited to the B, R, S, and N. Actually, these requirements are exactly the resident sensor requirements as well.
DG: Anything else on that SAT waiver?
(source: Andrew Bassett, ATP)
AB: We do now have some documentation requirements, too. Again, before there were no requirements there. Now you have to list the equipment that you’re doing the waiver on, you have to identify the control sensor, what type of sensor it is, plus what the additional sensor is used for the sensor relationship test. You have to list out the date of when the control and the additional sensor to be used, when they were installed, and when they were replaced or recalibrated. You have to list out the run number and date, so that when you are completing the production cycle on a weekly, you have some kind of easy identifier to tell you that it was done on run #ABC123, and the date was 9/8/20, so we can go back to the records and verify it. Date and temperature of the recent TUS and the documentation, that weekly log, are necessary; we need to see that weekly log as well.
We finally put some teeth into the requirements of the SAT waiver. I don’t think it’s going to be a big change for a lot of the suppliers out there. They will have to change over that one sensor, but, for the most part, I think we tweaked it enough where we felt more comfortable, especially changing those two different sensors so that we didn’t have drift occurring at the same time. That was our biggest concern as a committee.
DG: So, you’re basically trying to ensure reliability and you’re going to actually test for what you’re testing for. That makes sense.
We talked briefly about the overall or resident SAT, the alternate SAT, and the waiver. If you, the listeners, have questions, be sure to email them into us and we can potentially get Andrew to respond to them. Send those to htt@heattreattoday.com. We’ll leave Andrew’s information at the end of each of these podcasts.
Andrew, I’ve got a final question for you, not dealing with any specific aspect of the revision, but just to give people a sense of the amount of time that folks in your shoes, people that have invested time or actually on the committee: How much time do you think you’ve invested in the rev F portion of AMS2750?
AB: It was a long process. To put it in perspective, we developed our sub team and had our first meeting back in October of 2017, during one of the NADCAP meetings. We were kind of on a fast-track to get this spec revised and put out there. It wasn’t actually released until June of 2020; so three year plus is a fast-track in the eyes of the AMS world. We did meet at least six or seven times a year, either during an AMEC meeting or during one of the NADCAP meetings, and we had numerous Webex calls. When we actually met face to face, they were good 8 – 10 hour sessions of hammering out the spec. Then, we would take it back to our own groups and muddle through what we discussed. It was a long period of time. I would hate to put an hour on it. I wish we’d gotten paid for that! Taking into account what our company is and what we do, we have to live, breathe and eat this spec, day in and day out, for our customers. I just wanted to be a part of the process of getting this documentation, so the world can understand the issues in pyrometry.
DG: I actually have one other question for you. You told us in the first episode how you got onto the committee. Are they always looking for people to participate on the committee, or do they carefully fence that and only invite in certain types?
AB: Anybody can be a member of AMEC. So anybody that wants to get involved with the revisions of any of these specifications, including the AMS2750, they’re more than welcome to show up at an AMEC meeting, get involved, and volunteer to get involved with the specifications. I remember my first meeting where the chairman said, “You’ve got to get on this 2750 team. And, oh by the way, we’re thinking about writing some other specs that we’re going to throw you under the bus for.” They’re looking for young blood to get involved with these specifications and be a part of it, so yes, anybody can get involved with these specifications.
DG: If you are listening and you’re one of those people that might be interested in participating in that, you can certainly get a hold of Andrew.
This was our second part in a three part series. Our last episode will be on temperature uniformity surveys, the issue of rounding, and quality assurance provisions. If you’d like to learn more or reach out to Andrew, you can go to www.atp-cal.com and look at their ‘about our team’ section in the main navigation bar. I’d also be happy to receive emails on behalf of Andrew. My email is doug@heattreattoday.com. Thanks for listening.
Doug Glenn,Heat Treat Today publisher and Heat Treat Radio host.
To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio and look in the list of Heat Treat Radio episodes listed.
In this first of a three-episode series on AMS2750F,Heat Treat Radio host, Doug Glenn, discusses Andrew Bassett of Aerospace Testing & Pyrometry discusses the significant changes in the specification in the areas of thermocouples and calibrations.
Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript.
The following transcript has been edited for your reading enjoyment.
Doug Glenn (DG): This past June AMS2750 released revision F, but what does that mean to you? We caught up with AMS2750F committee participant, Andrew Bassett, to find out. Our conversation about this revision will stretch over 3 episodes with the first dealing with thermocouples and sensors, the second dealing with system accuracy tests and the third, temperature uniformity surveys. This first episode will be all about thermocouples, sensors and calibration.
Andrew, welcome to Heat Treat Radio. We're excited to have you to discuss this AMS2750F revision. If you don't mind, why don't you take a minute and introduce yourself to our listeners?
Andrew Bassett (AB): I'm president and owner of Aerospace Testing & Pyrometry, headquartered out of beautiful Bethlehem, Pennsylvania. I've been in the aerospace pyrometry field for going on 30 years, after graduating from college at Davis and Elkins college in Elkins, West Virginia with a degree in communications. I discovered by myself that I would end up starving in radio broadcasting, which my field was, and got involved with a company called Pyrometer Equipment Co., a family owned pyrometry business. They needed some help as they were expanding operations, and it was the father of my girlfriend (at the time)—now my wife--who had started that business in 1956. That's how I got my break into pyrometry.
Davis and Elkins College (photo source: dewv.edu)
This was also the time when NADCAP was starting to put its foothold on the aerospace industry. I kind of self-taught myself in the ways of aerospace pyrometry. I spent many years getting to know the specification and understanding what the requirements were, dealing with the auditors themselves, and having them teach me about what they look for during audits. I've taken that knowledge with me for the last 26 years.
After I left the family business, I worked for another start-up company in the field of pyrometry, left that company, and worked for a large commercial heat treat company based in the Southeast as their pyrometry director. At that time I started to feel like I wanted to start my own pyrometry business. So, in 2007, I started Aerospace Testing and Pyrometry (ATP). I was doing it part-time for a while, but then in 2009, I decided to go full force. To this day, it is not just me anymore: there are 16 of us in the company which is spread from coast to coast to take care of pyrometry services as well as other things we have branched off in with ATP. I call it our four headed monster. We have our pyrometry services, which includes calibration and testing of thermal processing equipment. We do get involved with other testing as well, like vacuum measuring systems for vacuum furnaces. We've also done humidity pressure gauges and gotten involved with different types of calibrations as well. Additionally, we have our laboratory, which is based in Ohio, where we do calibrations of secondary standards and field test equipment. Finally, we have our consultant and training arm, with which we have a full-time ex-NADCAP auditor on staff who is able to assist our customers with pre-assessments of NADCAP audits.
AMS2750 is the main aerospace material specification in pyrometry. If you actually try to do a Webster's Dictionary search on pyrometry, you'll find it is a made-up word. We've interpreted it as the calibration and testing of thermal processing equipment; that is, heat treating equipment and any type of thermal processing will fall under this specification when it comes to testing.
AMS2750 has also now been adopted by others; it is not just a heat treating specification anymore. Two years ago, the FDA adopted AMS2750. Those facilities that are heat treating medical implants or dental drill bits will now have to follow the requirements of AMS2750. The one industry that walked away from this specification is the automotive industry. They have their own requirements called CQI-9. I always make a joke that the one good thing about AMS2750 in dealing with aircraft is that we don't see planes falling out of the sky, but we do see a few more recalls on automobiles and automotive parts.
DG: Just as a little preview for our listeners, Heat Treat Radio will be doing probably a two to four-part series, similar to what we're doing here with Andrew, on CQI-9, so stay tuned for that.
Andrew, how exactly did your company get involved with AMS2750?
AB: So, they had started to revise—and this goes back several revisions ago—revision C to create revision D. Revision C, I always said, was the Bible: You can give it to 100 different people and you would get 100 different interpretations. It was a much-needed change that was needed in revision D. At this time in my career, I only had about 8 years experience in pyrometry, but I had to live and breathe this document day-in and day-out. So, I approached several members from the AMS2750B team to get involved with the spec. I didn't have the great experience like some of the other members of the team who were from Boeing, Bodycote, and Carpenter Technology and other folks, and they said, “Well, we kind of have our team set into place. We'll ask you questions if we need anything.” I didn't hear much from them, but one of the team members did keep me posted of some of the changes.
Then when it came to the rev. E, I heard rumblings that they were going to revise the spec again, and it was at this time that I decided to attend an AMEC meeting. AMEC is basically the think tank of all of the AMS specifications that are dealt with. AMEC stands for the Aerospace Metals Engineering Committee. The various segment specifications fall under various commodity groups, I believe it's A thru H. AMS2750 is actually owned by committee B for NSAE. So AMS guys write the specifications, the commodity committees own the specifications and that's how this process works.
I did attend my first AMEC meeting and the chairman at the time was a gentleman from Lockheed Martin. Anybody can join the AMEC meetings and be a part of them, but at that meeting he asked who I was and my background. I told him and said that I wanted to get involved with this specification and he said, “By all means you need to get involved with this specification. Since you do this for a living, I think we'd like to have that perspective.” So that's how I got on the AMS2750 team for rev. E. I'm still young enough, and dumb enough, to keep going on to this revision of rev. F and will probably be around for the next revision after that.
I did have my inputs in both the specs. We had a great team for rev. F which included myself, Doug Matson from Boeing, who has since just retired, Marcel Cuperman, who is a staff engineer for heat treating for PRI NADCAP, Cyril Vernault from Safran Aerospace, (he is also the heat treat task group chairman in NADCAP), Brian Reynolds from Arconic, Douglas Shuler from Pyro Consulting and a NADCAP auditor, and James LaFollette from GeoCorp. Our team has consisted of people across various parts of the industry. From Arconic’s standpoint, we were looking from the raw material producers. Obviously, with GeoCorp, it was from the thermocouple side of things. And from Cyril Vernault based in France, we wanted the European influence of what's going on over there. So, a good, broad range of people from various sectors of the industry are involved with the specification.
[blocktext align="left"]“I'm an end-user, so I'm able give my input and say, ‘Hey, this doesn't make sense. What you want to add into the spec is not real world.’”[/blocktext]One of the things I always had in my mind when I first got involved with the specification was that the specifications were written by the aerospace "primes," but that's not the case; it involves people, such as myself, who are end-users of this specification. I'm an end-user, so I'm able give my input and say, “Hey, this doesn't make sense. What you want to add into the spec is not real world.” It’s nice that people such as us get involved with these specifications.
DG: Let's talk about the main sections of this specification. If you break them down, what are the main sections?
AB: There are really only five sections of the specification. You can break it down into thermocouples, calibrations and thermal processing classification, SAT (system accuracy testing), TUS (temperature uniformity surveys), and the very last five or six paragraphs are on the quality provisions (what happens if you have a failed test). Those are the 5 main sections of AMS2750.
DG: So focusing on the topic of this episode, thermocouples and sensors, let's highlight some of the profound changes that have been made in rev. F. First, what are the biggest changes regarding thermocouples and sensors?
AB: The bigger changes relate to how we address some different thermocouple types that were not addressed in previous revisions of the spec. In rev. F, we added and gave a thermocouple designation, type M, to Nickel/Nickel-Moly thermocouple. These thermocouples have been around for a long period of time. We do know that they're being used in aerospace application, especially at very high, elevated temperatures. It's more cost-effective than going into the platinum or the noble-based thermocouples. Type M was one of the newer thermocouples we added.
We also addressed the use of RTDs, which is, again, something that we had seen in the aerospace industry for quite a while. As I mentioned before, this is also a crossing over from the heat treat world into the chem-processing world. A lot of these chem-processing tanks use RTDs to measure chem temperatures, so we thought we better address these type of thermocouples.
RTDs in AMS2750F explained (photo source: Andrew Bassett, ATP)
Then we also added refractory thermocouples, which people weren't all that familiar with, unless you're dealing with the hot isostatic pressing (HIP) process. We're seeing more and more of the HIP furnaces out there now, with all of the additive manufacturing that is going on. We see people adding HIP furnaces everywhere, and a lot of those HIP furnaces are coming with type C thermocouples, because they are rated for these elevated temperatures that the HIP processes do. I think the type C thermocouples are rated close to 4,000 degrees Fahrenheit. We had to add some of these extra sensors that have been around for a while, but we wanted to bring them out a little bit further.
One of the other changes that was pretty significant—though I don't think it will affect the industry all that much—is that now we require thermocouples to be accurate to what's called “special limits of error.” The previous revision allowed for two different types: You were allowed special limits of error, which the accuracy is + or –2 degrees Fahrenheit, or .4% of reading. That was only required for a system accuracy test sensor or for a sensor that was being put in a Class 1 or 2 furnace. All other sensors, such as TUS of load sensors, and class 3-6, we allowed for standard limits of air, which was + or –4 or .75% of reading, whichever is greater.
We did some polling of major thermocouple suppliers out there. With my personal experience and that of some of the other people on the committee, we kind of said, “Hey, you know what? No one really orders the junky stuff, the standard limits; everyone orders special limits of error.” James LaFollette said, “Come to think of it, I don't think I've ever seen a purchase order that says give me the crappy stuff. We all order special limits.” So that's what we discovered – that no one was ordering the bare minimum because there wasn't a price difference between the two. Everyone had already been ordering the good stuff, so we just made that a little bit of a tighter requirement. Again, I don't think it's going to affect any suppliers out there.
I think the biggest change, when it came to thermocouples and sensors, was a big restriction that we put on what's called “expendable test sensors.” This was dealing with the base metal thermocouples. Base metal thermocouples are type K, type J, type T, type N, type M, and a couple other type base metals.
Click to read the Heat Treat Today article on thermocouples.
Primarily in the heat treating and thermal processing world, you pretty much see the K, J, N, and T. We had done some studies as a sub-team within 2750 to look at the drifting of thermocouples, that is, where thermocouples start to lose their accuracy. In the previous revision, we had some provisions in place that allowed people to use these expendable thermocouples that were attached to a temperature uniformity survey rack and were preserved. They could use them up to three years or 90 uses when below 1200 degrees. We thought that seemed kind of excessive on a 20-gauge wire that is covered with fiberglass coating. They're probably not going to hold up, but maybe we should see if there is any drifting of these thermocouples. So, we had one of the major thermocouple suppliers, Cleveland Electric Lab, run some drift studies on type K thermocouples, and we found out that these wires were actually starting to drift after three or four runs. The drift study included a cycling test where they ran it up to temperature and back down 30 different times. We asked, “Why don't we try to simulate how these thermocouples are going to interact coming in and out of thermal processing equipment? Why not pull them out every single time and do it that way?” Again, we found that thermocouples were drifting even further and even quicker.
At this point we decided we better put a restriction on this, and that gave the biggest uproar regarding the reuse of these thermocouples. Previous drafts before the final release of the spec was, if it's used above 500, your expendable wire is one and done above 500 degrees. A lot of the suppliers out there came screaming and said this is going to cost us millions and millions of dollars more in thermocouples. But we stood firm and said, “Hey look, if you're using these test thermocouples to validate your furnaces, either through a system accuracy test or uniformity survey, you really do not know what your error of that wire is after the first use.”
Most of the major thermocouple suppliers will even state on certifications that they will only guarantee accuracy at the time of calibration. Once it goes in a furnace, atmosphere and different conditions of the furnace will affect the wire. We stood our ground, but we ended up backing off a little bit. If you were using them strictly below 500, you're allowed to use them for 3 months (90 days) and you're going to have to keep a log. If you're using them between 500 and 1200, we're going to allow you to use them for 90 days, but now you're only restricted to five usages. And then again, above 1200, you use it once and throw it away. That was probably the biggest hassle, trying to get that. We did finally compromise on that three month or five usages. I do see the burden on the suppliers because they were used to three years or 90 usages, so now it's down to three months or five usages.
DG: I see on the chart that I've got here in front of me that base metal types of M, T, K, and E are all the three month or five use, but you've also got base metal type J and N which is three months or 10 uses. But all of them, above 1200, one and done.
Table for SAT and TUS Sensor Reuse (photo source: Andrew Bassett, ATP)
AB: Correct. That's one of the things I was trying to explain to some of the suppliers that were having heartache about the original change of 500 one-and-done. We only left it to the types M, T, K, and E; we always left this out of types J and N. My personal experience with type J has been (and we've switched over to type J wire a while ago for testing below 1200 degrees),that it's a little bit cheaper in price than the type K wire, and there was always this allowance for doubling the amount of usage if you just switch over to type J or type N.
DG: We have a few significant changes in the area of calibrations. What's another area of change in this section?
AB: One of the big things which really surprised me when we wrote it into the standard, but which was kind of overlooked by some of the suppliers, was the requirement of test instruments to have a .1 readability. So when it deals with test instruments and also now data acquisition systems. Now, if you have a chart recorder that is on your furnace (most people are going to data acquisition systems, some sort of SCADA systems), that recorder must have a .1 readability. That caused an uproar since that may create big changes.
Now, we don't put out these changes because we think it's a good idea; AMEC is data driven. The big thing with the .1 readability is that we were actually fixing a flaw that has been in the spec since the first day it was written, when it was just rev. A. We allowed for percentages of readings for your accuracy requirements. Let's say, for instance, on your instruments that are on your furnace calibrated controller an if it's in Fahrenheit, you're allowed + or –2, but if it's in Celsius, it has to be + or – 1.1. And if your instrumentation doesn't show .1 readability, how can you show compliance? That question is one of the reasons—that is, fixing a flaw in specification.
(photo source: www.atp-cal.com/laboratory/)
But we also allow for percentage of reading, which is + or –2 Fahrenheit or 1.1 Celsius or .2 % of reading, whichever is greater. Let's say you have a calibration point at 1400 degrees, you're actually allowed an error of 2.8. If you can't show that decimal point readability, how can you show compliance? That was one of the biggest issues.
Originally, the first draft said all digital instruments need to be .1 readability and then we backed that off to only say that the data acquisition system had to be .1 readability. At the end of the day, the recorders or the data acquisition system is the proof. As long as that shows the tenth of degree of readability, and it meets the requirements, then you're good to go there.
We did look at how many customers are already using digital data acquisition systems through NADCAP. There's actually a NADCAP checklist question that talks about chart speed verification, and if you answer that “N/A” then you obviously have digital data acquisition. At that time, we did look at that data and 78% of the NADCAP heat treating suppliers out there already had paperless systems. On top of that, two years after the release of 2750F, so as of June 29, 2022, you're not allowed to have paper chart recorders anymore. Everything is pushed to a digital data acquisition system 2 years after the release of this spec. I'd say, that's another one of the bigger changes when it deals with the instrumentation.
So the biggest changes are the .1 readability for your chart papers and the two years after the release requirement to go with a paperless system.
DG: Now question three: What are the changes that were made in the calibration section?
AB: There were a few changes when it came to calibration.
One of the things we added this time was the calibration of timing devices. A lot of facilities have timers or clocks that they're basing their times and temperatures, and again, there was no requirement to calibrate this. Therefore, we added a whole section on calibration of timing devices.
There was some push back on that. Certain people, who have suppliers who use certain control operated by computers and which are always synchronized in their server systems, asked if they were going to have to go out and buy calibrated stopwatches and sit at their PC to make sure it's within these new requirements. We finally said, no, you don't have to do that, but if you can procedurally address how that whole system works—that your server is always verified—you would be okay as long as you procedurally address that.
Again, we were loose on the accuracy requirements. Some of these external devices that you have only need to be calibrated every two years. Comparing it to people's standards that they use—we personally do calibration of timers as well, and our standards are required to be calibrated every two years—we ended up just tossing these devices away because it's more expensive to send them back for recalibration than it is to buy new ones. So, we gave some of the suppliers an easier way out. But we just wanted to address, again, something that has never been brought up in the specifications, which, though not technically dealing in the pyrometry world, does sit on furnaces. We need to get these things looked at every now and then as well.
[blocktext align="left"]“So, we gave some of the suppliers an easier way out. But we just wanted to address, again, something that has never been brought up in the specifications, which, though not technically dealing in the pyrometry world, does sit on furnaces.”[/blocktext]Some of the other changes come in the documentation. We did change some things that need to be required for the documentation of your calibration results. One of the things was that we need you to document the sensor that you're calibrating for that particular piece of equipment. For instance, you have a vacuum furnace and most vacuum furnace control sensors are a noble metal type S or type R thermocouple, but then the load thermocouples that measure the parts inside might be set as type K or type N. We just want you to denote that the control system is type S and the load thermocouples are type K. Not real big game changers, it's not going to cause too many issues out there from the supplier base, it's just adding basically another column in your calibration reports to say what sensor you're calibrating.
We didn't go too overly crazy on the calibration portion. The one thing, kind of in the calibration field, is we did add a new instrumentation type. When you look at thermal processing equipment, it's broken down into two different sections. You have your furnace classification which is your uniformity tolerance and then you have what's called your instrumentation type. You have class 1 - 6 and you have instrumentation A – E, now instrumentation D+. This was more for Safron Aerospace. Cyril Vernault was very adamant that we add this D+ instrumentation because Safron's specifications state that they want this extra sensor that is basically 3 inches away from the controlling sensor, so they can measure if there is a big difference between these two sensors to determine if there is drifting of your thermocouples. So we added this new D+ instrumentation. We didn't realize this was big over in Europe, but it was nice to have someone like Cyril say that a lot of European suppliers use this and that he’d like to see it in AMS2750. Again, having this broad range of people on the specification helped us find out what's going on in different parts of the world.
DG: How about we close with the fourth part of thermocouples? Could you delve into the expanded section on offsets?
AB: Absolutely. Always one of the areas, especially when it comes to NADCAP audits, is the use of offsets. We basically broke it down into two different types of offsets that are allowed. We have what's called a correction offset, which is basically either a manual or electronic means to bring an instrument back to a nominal temperature. And we have a modification offset, which is just the opposite. It takes either a manual or electronic offset or a shift in the temperature to bring it away from nominal. There are different ways that people have used these offsets. For instance, let’s say you go into a facility and you're doing your calibration of a controller, and the instrument is off linear by two degrees. People would use the offset to bring the instrument back a nominal temperature. Instead of maybe doing a full factory calibration, they would just go into the instrument, hit some magic buttons, and (say I need to offset it -2 because my instrument was two degrees high) set a two degree correction offset.
A modification offset generally is only going to be used for when you're doing a temperature uniformity survey. Let's say it is skewed to one side of your temperature median. For instance, (I always like to use this in my pyrometry training class), we know temperature uniformity and I go in and do a temperature uniformity on your furnace at 1000 degrees. I have to hold it to be + or –10. When I get my final results and I look at everything with all my calculations, I have a survey that actually comes out to be 992 – 998 degrees. It's well within the + or –10, but it’s skewed down to the lower end.
So, there's different things you can do to try to correct that. Maybe change air flow, or thermocouple location, but a lot of time, what happens is you get a furnace that was made in the 1940s and you're trying to make it comply to 2020 specifications. The only thing you can do is go in and shift the controller away from the nominal to actually make it read hotter. In this example that I'm giving you, what I would do is go in and put in an electronic offset and tell the controller to read colder now, as I will drive more heat into the furnace. So, I go in and put a -5 degree offset into the control and now, in theory, when you do the survey, you're shifting that temperature up by five degrees. Now if you look at that split, it would be 997 – 1003—it’s more centered around your set point temperature. That would be what's called a modification offset. You're taking that TUS distribution and skewing it to better center around the set point.
We really did some “spelling” on this: we put some maximums, the amount of offsets that are allowed as we don't want people to go too crazy on these things, so we did put some offsets in there. But I think we did a great job of trying to spell out what these offsets are being used for, how you're supposed to document them, and make sure that you're consistent with your practice every time. Again, procedures will have to be written to fully understand how you're going to do the offset. Am I going to put it electronically? Am I going to do a manual offset, just shift my temperature up five degrees because I know my furnace is cold by five degrees? I think with that whole new section in there, I think we did a good job of spelling that out for the suppliers.
DG: Thanks so much, Andrew for joining us on the podcast.
AB: Thanks for having me, Doug. Looking forward to chatting more with you about AMS2750F.
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