It is not possible to upgrade steel with a set of impact tests; this is a very big misconception in the industry – indeed, a very dangerous one.
Many people in the steel industry believe that if one conducts a set of impact tests at -20°C and they pass, that this JR material is now compliant with the J2 requirements. This is not at all true. The difference between J2 and JR material is as follows. The Charpy Impact Test measures a metallurgical parameter of the engineering material called the ductile to brittle transition temperature (DBTT). Steel transitions from ductile to brittle at a specific temperature. For JR material this temperature will be around 5°C or so. For J2 material this temperature is much lower less than -20°C.
If one takes a set of impact tests from a piece of JR material and it happens to pass the J2 requirement – in other words, for that set of impacts the DBTT is less than -20°C – it does not mean that all of the material complies with this requirement. This was just a lucky test. It DOES NOT mean the whole batch will pass, and the chances will in fact be that it does not pass. In fact, some laboratories even conduct more than three sets of impacts before a set passes and then regrade the material, with the full knowledge that some of the tests failed.
The DBTT and therefore the designation of the material being JR or J2 is controlled by the hot rolling schedule at the steel mill. The mill has to control the hot rolling process more tightly to achieve the enhanced properties of the J2 requirement. Therefore, it is not at all possible for the JR material to be upgraded to the J2 requirement. If this were the case, why would any steel mill put tighter controls on hot rolling and manufacturing of J2 material if they could just make JR material and conduct one set of impact tests? The sinking of the Titanic is an example of a lack of understanding in those days about the DBTT – no one knew that when the ship hit the iceberg, it would fracture. Essentially in those days JR material was all that was available – advances in hot rolling processes only occurred later. Hence, the ship broke in half.
The risk of this practise, which unfortunately seems to be common in the industry, is catastrophic failure. The “regraded material” could be exposed to cold conditions and because it does not have the right DBTT, it could fail catastrophically. This could cause injury, loss of life, capital loss and other significant losses. In a failure situation such as this, the responsibility for the loss would be entirely on the manufacturer or fabricator because the steel mill never sold J2 material – they only sold the guaranteed JR material. Steel merchants who conduct the tests and sell it on in the upgraded form are taking a severe risk, but if there is a failure the risk is not removed from the manufacturer. It is only the steel mill that can classify the material as JR or J2 or J0, for that matter.
There is a further misconception that the AIA (Authorised Inspection Authority) inspectors sign off this upgrade of the material. This is not what the AIA’s are doing at all. The role of the AIA is to VERIFY the test result that reads on the machine is recorded correctly to the sample number by the technician. The AIA is not there to upgrade the material and is not empowered in any way to upgrade the material, nor can they check that the test was done correctly. The testing is the sole responsibility of the laboratory and the lab cannot upgrade the material either. The only way the end user of the lab results can have any assurance of the test method and traceability is through the ISO 17025 accreditation. This accreditation means that method validations must be done, measurements of uncertainty and calibrations are carried out – and so forth. The only role of the AIA is to verify the result recorded by the machine is the result reported. The AIA cannot comment on the result itself, and they certainly cannot comment on the certainly not on the method or the correctness thereof.
One Eighty is a SANAS accredited ISO 17025 facility which means that any test report that comes out of the lab is verified by way of the quality management system and the audit by SANAS. It is also therefore not required for an AIA to witness any test in our lab as they can provide no further value.
It is not possible for either the lab or an AIA to upgrade steel from JR to J2. This would be compared to asking a lab to upgrade a slab of chocolate to ice cream.
Unfortunately, there are labs that are not run by metallurgical engineers who don’t understand the concept and as a result market upgrading steel from JR to J2 as a service. It is extremely dangerous that this has become accepted practise in the industry, and it should be notes that metallurgical testing is a professional service and should be conducted by professionals so that the basic understanding of metallurgy underpins what is done for the industry. Metallurgical testing is a key risk mitigator for the fabrication and manufacturing industry – the total risk of the performance of the welded item is tied up in the metallurgical testing.
It is extremely sad that there are manufacturers and fabricators that wish to devalue the importance of the metallurgical testing service and not make use of professional organisation who can properly mitigate the risk.
This practise could eventually result in a catastrophic failure, just like the sinking of the Titanic, because the regraded steel simply does not have what it takes to perform in the cold conditions – it will fracture.
For more information on this, please contact Dr Janet Cotton on firstname.lastname@example.org