Regarding the issue of the low-temperature impact temperature for forgings
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Previously, a set of drawings was designed for equipment with an MDMT temperature of -5℃. The design institute required that the forging material be 16MnD, and the engineering drawings specified that these 16MnD forgings should undergo low-temperature impact testing at -40℃. However, according to the NB/T47009 standard for forgings, 16MnD forgings with a nominal thickness of ≤100mm are required to undergo low-temperature impact testing at -45℃ (all the equipment in question has a small diameter, so the nominal thickness of its forgings is less than 100mm). Therefore, the supervisor now claims that the low-temperature impact temperature specified for the equipment’s forgings does not meet the requirements of the standard. We explained that the MDMT temperature for this equipment is only -5℃, and that the standard specifies this as the minimum operating temperature for forgings made of this material; the impact temperature we are using is much lower than the MDMT temperature. Yet the supervisor still refuses to accept this explanation. We would like to ask if such a situation indeed violates the regulations? Can’t it be given like this?
In my opinion, the supervisor is right – -45 degrees is the impact temperature within a specific thickness range specified by the standards for forgings. If the certificate states that the forging was tested at -40 degrees for impact resistance, then it does not meet the requirements of the material standards; and this is not the same as determining whether the forging can be used or not.
I agree with this. A few days ago, a colleague attended training for pressure vessel auditors, and the instructor explained this point in detail: it is necessary to meet the impact temperature requirements specified in the standards first; only after that can this material be used. Even if there is a large difference between the material’s minimum design temperature and its impact temperature, with plenty of margin available, the impact temperature requirements set by the standards still must be met first.
We also have some equipment made of Q345R/16Mn material, with an MDMT of -9°C. The engineering drawings provided by the design institute require that the material undergo impact testing at -9°C. Based on this, since the standards specify impact testing only at 0°C or -20°C, does that mean we can only conduct impact testing at -20°C? Is it wrong to set it at -9℃?
Indeed, the standard specifications clearly state that it is necessary to follow those specifications, and the special inspection agency is very rigid in this regard.
This post was last edited by zjq1962 on 2022-7-8 09:53. Material standard specifications and re-inspection of materials are two different things; it would be best for the original poster to upload a diagram to see how the technical requirements specified in the drawings are laid out.
I used to think that it was sufficient for the temperature to be no lower than that of MDMT. From what I remember, the equipment shown in the drawings provided by design firms in the past also had requirements regarding low-temperature shock other than 0°C or -20°C; it seems I need to pay more attention to this going forward.
When I encounter such problems, I usually contact the design institute; it’s not necessarily that the temperature specified by them is incorrect – it’s possible that they use different standards. It would be best to be able to explain things clearly to the Special Inspection Agency; if that’s not possible, we’ll have to follow their decision.
It is either a retest or the impact temperature specified on the material’s certificate of origin. The drawings are prepared based on the engineering drawings from the design institute, specifying that the 16MnD forgings be subjected to low-temperature impact tests at -40°C.
The design specifies that the impact temperature of the material meets the usage requirements, and the design institute confirms that there are no issues with this
Well, after going around once, they threw us in there. Actually, during the design phase it was found that this didn’t meet the standards for forgings; it was my mistake due to a misunderstanding. Fortunately, only a few pieces from this batch were processed urgently, so the forging factory was asked to take samples from the pieces that hadn’t been processed yet and conduct impact tests at -45°C. :(