Procedural issues regarding technical contacts
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Recently, I encountered a container unit in which the weld between the lower head and the cylinder of its original design used a welded structure with gussets (double-sided welding was not possible due to the absence of manholes). The drawings provided specifications for this weld: 100% RT inspection was required, with a weld factor of 0.9; for the other Class A and Class B welds, 100% RT inspection was required as well, with a weld factor of 1. Now, the welding process developed by our company’s welding engineers involves using TIG welding for the root pass and automatic welding for the cover pass. This welding structure in the drawings uses an old-fashioned welding method, as argon arc welding technology was not yet developed at that time. The question now is: is it necessary to contact the original design firm? There are currently two opinions: 1) We will use our own welding processes (furthermore, our company does not have any welding process evaluations for processes involving gaskets), so it is not necessary to contact the original design team. 2) Since changes have already been made to the drawings, and it is a main weld, plus it can be seen from the photographic film as well, are changes still necessary? So, what follows from this question is: What authorities does our company have (i.e., the corresponding design and manufacturing qualifications) to make relevant changes to the original design without having to contact the original designer? Please explain in detail.
Written consent from the original design unit must be obtained.
Following the practices of my previous manufacturing plants*, I simply followed our company’s welding procedures. After communicating with the design team, it became clear that they didn’t understand these procedures either. The larger the design firm, the more specialized the roles become; those in charge of design don’t know anything about welding, and they’re unaware that using shims will result in failures in inspections. I’ve worked on design as well as on riveting and welding processes. The welding groove diagrams provided in the design drawings are only for reference by the manufacturing plant; ultimately, our own welding procedures must be followed. I’ve encountered situations where 80% of the RT tests failed due to the use of shims, so we stopped using them altogether. Among the qualified criteria for fellow welders, there is an issue related to coverage marked with a K; those without a K can weld those with a K, meaning that welding without a backing plate represents a higher level of skill. One last question, sir: are you sure that your welding process of using TIG welding for the root pass and automatic welding for the cover pass is feasible? No manual arc welding in the middle? Not afraid of burning through?
I just checked the NB standards – there is no need for re-evaluation when removing or adding gaskets; therefore, whether the evaluation was done with gaskets or not doesn’t affect your ability to change the gaskets
Bro, you’re absolutely right: many design firms that handle design work don’t understand manufacturing processes at all. The actual difficulties faced by manufacturing plants have nothing to do with them, and design changes are not used as a basis for evaluating their work. Being conservative, inflexible, and unwilling to take any risks are characteristics of those who have been working in design for a long time; these traits are sometimes also considered advantages. I remember there was such a device: a horizontal tank equipped with a steam drum (DN300×18, length 1400, material Q345R). We submitted an application for a design change to use Q345D pipes as a replacement (for re-inspection purposes), but the request was denied. Let’s think about it: how to roll DN300×18? Where can we find a rolling machine with such capabilities? This forces us to use pipes, issue fake material sheets, and create fake welds and fake parts. As a manufacturer, one should naturally revere regulations; fraud is absolutely unacceptable. But isn’t there also a problem with those who are the original designers? Additionally, the welding process naturally involves TIG welding for the root pass, manual welding for the fill pass, and automatic welding for the finish pass. (Automatic welding: The thinnest steel plate we have used is 6mm thick Q345R, with welding flux placed on its back side.) It’s fine to figure out the welding parameters as needed.)
There’s definitely no issue with 6m automatic welding; I’ve conducted welding evaluations for over 50 different processes, including Fe1-8, gas shielded welding, TIG welding, automatic welding, and electrode-clad welding. I’ve never tried using TIG welding in automatic mode, as TIG welding only allows for a thickness of 2-3 mm per pass, which isn’t efficient enough. I wonder if you guys have ever tried performing two automatic welds, one on the front side and one on the back side, on plates with a thickness of 8-10 mm. I heard from small manufacturing plants that this method yields a fairly high success rate; however, our factory is too cautious to give it a try.
We have manufactured LNG double-walled tanks, with the outer tank made of Q345R material with a thickness of 6 mm. Full-automatic welding is used on both the front and back sides; however, a welding flux is required as a protective layer on the back side. After automatic welding, gas tungsten arc cutting is used to remove any residual material (just a slight scraping), followed by another round of automatic welding. The efficiency is quite high, but it’s important to maintain the correct welding parameters (current, voltage, welding speed are all crucial)
As per the regulations, any deviation in your manufacturing process from the requirements specified in the drawings (such as material substitution, structural adjustments, welding methods, etc.) requires permission from the design agency. Currently, since each manufacturing plant has its own welding assessment procedures for welding processes, the design agency and the special inspection institute do not require that the welding method used be identical to that specified in the drawings; however, it is necessary to meet the design requirements, and the design agency must be informed and give its approval.