In the design of large storage tanks, why shouldn’t the nozzles interfere with the welds on the tank walls?
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This post was last edited by forowhl on 2024-12-20 at 11:19. Below is a screenshot from page P8 of GB/T50128-2014, which explicitly states that it “should not be done”. Given the high pressures and wall thicknesses of pressure vessels, GB/T150 stipulates that \"it is advisable to avoid Class A and B welds on the vessel shell.\" It is generally easy to avoid welds when designing the nozzles for large storage tanks, but sometimes, due to layout considerations, it is only discovered during manufacturing that they interfere with the circumferential welds of the tank wall, making it difficult to make adjustments.
150 itself implies that one should avoid it; if avoidance is not possible, then calculations must be done regarding loss-free operation and so on. Since large storage tanks are of such a large size, in the design phase, the weld layout must take care to avoid areas where connections are made. Manufacturing is carried out according to the design specifications, not after it turns out that there are discrepancies between the actual construction and the design.
It’s indeed true that this should be avoided in advance, but if it happens anyway, shouldn’t the entire storage tank be scrapped just because of the issue of welds that cannot be avoided through some kind of takeover measure? I think, following the practices for pressure vessels, 100% RT or UT of the welds would be sufficient, but the standards do not allow this.
Although it is at atmospheric pressure, the stress level of the steel plate is not necessarily low.
There’s nothing we can do; APIs are allowed, but national standards do not permit it
In which chapter is the API described? Not found. :L
5.7 Shell Openings: The types of openings include those that interfere with longitudinal welds as well as those that interfere with transition welds
Thank you for the guidance; I have found the relevant provisions. However, the owner’s consent is required, and it is also relatively difficult to implement.
It’s a bit strange; longitudinal welds can be avoided during the layout phase, but what about circumferential welds? The height of the pipe opening is fixed; how can the pipe opening be avoided in relation to the circumferential weld?
1. Stress concentration: The interference between the nozzle and the wall panel welds can cause stress concentration near the welds, increasing the risk of weld cracking. Especially during water filling tests or tank operation, factors such as liquid pressure and temperature changes can cause the stress near the welds to increase further, thereby accelerating the fatigue and cracking of those welds. 2. Residual stress: The residual stress generated during welding may also increase due to interference between the fittings and the wall panel welds. These residual stresses may cause fatigue damage to the welds during the long-term operation of the storage tank.