We recently delivered a live online demonstration of the analysis of aluminum and steel alloys with OES, covering reporting, data management, grade identification and maintenance. If you missed it, you can watch the recording here.
We gave those attending the opportunity to submit questions. Since these could be interesting to any OES user we’ve answered them in this article, partly more detailed than in the in the scarce time of the live demo.
There are two ASTM standards for OES inspection of stainless steel: ASTM E415 and EASTM 1086.
ASTM E415-15 is the Standard Test Method for Analysis of Carbon and Low-Alloy Steel by Spark Atomic Emission Spectrometry. The standard covers many common elements, but the element of particular interest is nitrogen, which must be controlled to very low levels.
ASTM E1086-14 is the Standard Test Method for Analysis of Austenitic Stainless Steel by Spark Atomic Emission Spectrometry.
It’s very difficult to give a definitive thickness because every material or alloy type behaves in a different way. For example, the behavior during the spark process of a 1-2 mm low alloy aluminum sample is different from 1-2 mm duplex steel and different again from 1-2 mm low alloy lead.
To give some direction, we can say that it is possible to work on 2 mm samples, but you must do an optimization of the spark parameters first to ensure that the individual spark doesn’t burn a hole in the thin material.
We have carried out analysis on thin steel sheets, with good results. For more specific applications, please get in touch to speak with an application specialist.
As we have seen in the question above, there is a minimum thickness of sample required, so it’s always recommended that the sample be above a certain thickness. However, as there are many types of samples, such as ferrous-based, Al-alloy, Cu-alloy or Pb-alloy, the technique of sample preparation will be different for each type of alloy. As a rule, use grinding for ferrous-based samples and milling for non-ferrous.
Find more detailed information on sample preparation in this article: Non-ferrous melt chemistry verification: it's all in the sample.
No, it is not possible to attach a portable head to the OE720 or OE750. This is because the OE Series of instruments are designed for high analytical performance as stationary spectrometers.
If you need a probe because your samples are very heavy, are not able to be cut, or are integrated into a larger system, you might be able to use the OE Series as the spark stand design is open on three sides and it’s possible to analyze irregular, large, or heavy samples.
However, if you do need a movable head, our mobile OES instruments, the PMI-MASTER Smart and the PMI-MASTER Pro2, fit the bill. They are very good for iron and steel applications, including nitrogen analysis.
Can we subtract the 0.1% error from the other steel samples tested, or are there better ways of correcting errors in tested results?
This is a great question, but a little too complex for a simple answer without looking into it further. However, general advice I would give is that there are a few things you can do to correct your OES results. The main thing is classic recalibration. Every instrument is supplied with standardization samples for each matrix. You can measure these to correct the original calibration on the instrument to compensate for the inevitable drift that occurs over time for all OES analyzers.
If you need to use user-specific standardization and have only one sample that represents your typical results, then you can use type standardization. As this topic is so important for reliable OES analysis, we’ve created a webinar that goes into more detail, and I would recommend watching this webinar on-demand: Best 5 Expert Tips for Optimal Non-ferrous/ferrous melt control with Spark OES.
You can use the function in the operating software called ‘concentration adjustments’ which is a manual type standardization.
Possibly, it depends on the age of your instrument. Please contact our service department with the serial number and they will be able to advise you further.
It does differ a little. The optical design layout is different for the OE750 compared with the OE720. This is because the OE750 offers a wavelength range from 119 nm. This means that the OE750 is equipped with a membrane pump and mid-pressure argon system. The difference in terms of the argon flush is that the OE750 might need a 10-minute flush prior to measuring the first sample at the beginning of a shift. The software includes a tool that tells the operator when the instrument is fully operational and ready to use.
This can be done via Hitachi’s GRADE Database, which contains all the grades for aluminum and other alloys. It’s very easy to select the grades you need and export them from the database library to your own instrument’s library. The GRADE Database is included with all our OES instruments and is updated annually free of charge.
Typically, ‘high sulfur steel’ contains sulfur at 0.3%. This should not be a problem for spark spectrometry. If you do have difficulty, then you can modify the pre-burn time or take several measurements on the same burn spot.
The issue with this, especially for free-cutting steel samples, is that you end up needing to use a very long pre-burn time to get accurate results. The OE series gets round this with the robust design of the spark source. This means that both the OE720 and OE750 can be pre-calibrated with the free-cutting steel method, making it simple to analyze high sulfur and high lead samples.
Our SpArcfire software offers a lot of features to its users. As you mention, the operator is able to carry out manual adjustments, however in terms of analytical procedure, we suggest that this option should be chosen last. There are many reasons that measured results might not match what you expected and some of them are not spectrometer related. For example, incorrect sample preparation, poor argon quality, or even running the wrong sub-program can all give anomalous results. We also advise that manual adjustments should only be carried out by experienced users.
All our spectrometers are factory calibrated and they all offer functions like recalibration and type-standardization to ensure reliable results can be obtained during the lifetime of the instrument. If you need more information on this, please get in touch and we can discuss further.
Regular maintenance and servicing are essential for all spectrometers and analytical instruments. Our OES instruments are all designed so that the daily routine maintenance, such as cleaning the spark stand and electrode, can be done easily by the operator. You can find detailed specific information on what you need to do for your instrument in the analyzer’s service and operation manual.
For calibration you will need to do a recalibration or type recalibration depending on what kind of samples you are measuring. As with routine maintenance, this is a simple procedure that can be carried out quickly by the operator. Again, the detail of this is within the software manual of the instrument.
For more information on maintenance and calibration, please get in touch to speak with one of our OES experts.
The OE720 and OE750 are stationary instruments delivering excellent analytical performance in terms of low detection limits and high precision. If we look at the actual ‘spark’ process, where a discharge between the sample and electrode occurs, any air present would interfere with the result. The ideal solution is to carry out the spark in an inert gas atmosphere, and argon is the preferred and most cost-effective gas.
It’s interesting to note that when reading various literature, OES is often defined as Optical Emission Spectrometry using SDAR, where SDAR is Spark Discharge Under Argon.
All Hitachi stationary OES use argon to provide the inert atmosphere. However, the argon consumption of the OE series is exceptionally low, thanks to its innovative design.
If you’d like to see the recording of the live demo, you can watch it here.
In our guides Optimal non-ferrous melt control with OES and Optimal melt control in cast iron with OES we go into more detail on the sample-taking process and preparation techniques to get reliable results first time when verifying melt chemistry. Download your copy by clicking on the links above or on the button below.Get the cast-iron guide Get the non-ferrous guide Watch the live demo recording