Issues regarding hydrotesting and heat treatment of horizontal vessels
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Double-saddle horizontal vessel, with a diameter of 5400 mm, a tangent length of 16000 mm, a wall thickness of 28 mm, and made of material Q245R. Currently, the designers have two opinions: one is that since all the design calculations are satisfactory, using a double saddle is sufficient ； Another reason is the fear of problems occurring during construction and manufacturing, such as the collapse or deformation of the cylinder body during hydrostatic testing and heat treatment, which necessitates the use of three saddle supports. I would like to ask experienced sea users: could the cylinder of the aforementioned container collapse or deform during hydrostatic testing and heat treatment?
The design calculations should include strength calculations for the hydrostatic test; if there are no issues with the design calculations, then there will be no problems with the hydrostatic test. As for the possibility of collapse during heat treatment, if there are concerns, the manufacturer can be asked to add a temporary saddle support during this process in order to increase stiffness. However, no problems should arise during heat treatment, as only the stress resulting from the container’s own weight is present, with no other external stresses. When designing, choose two saddles; try to avoid choosing three saddles.
Temporary support is advisable during heat treatment, as the design in this regard is often inadequate. It is difficult to find the strength values at the annealing temperature calculated during heat treatment; basically, there are no official data available for the strength of Q245R at annealing temperatures of 600–650 degrees.
Thank you! Using three saddles is indeed rather troublesome. The idea of using three saddles stems from the fact that in previous cases where similar containers were pressurized, no additional support was provided, resulting in significant deflection of the cylinder between the two saddles.
Heat treatment is generally only something for which manufacturers have practical experience; whether support is needed must be determined by them based on the actual situation.
Yes, the problems that arise during use are determined by the design, while temporary issues that occur during the manufacturing process are decided by the manufacturer.
No saddle is needed; temporary fixtures can be used during heat treatment. If collapse occurs during the hydrostatic test, then the equipment design is inadequate; the design must take into account both the conditions of the hydrostatic test and the most severe operating conditions.
Our company has encountered situations where the stress verification during the double-saddle hydraulic testing failed; the main issue was that the equipment became extremely heavy after filling it with water, reaching almost 400 tons, and since the shell was relatively thin, a 4-saddle setup was used (a 3-saddle setup didn’t work either, as it wasn’t possible to reinforce the structure, and the circumferential stress verification failed).
Using a double saddle will work fine if it fits, but choose a saddle with a 150-degree arc; the gasket plate must not be thinner than the cylinder. Heat treatment: this operating condition is not taken into account during calculations; it is recommended to use a temporary saddle as required by the heat treatment procedures.
I’ve learned that a 400-cubic-meter horizontal tank is indeed very large
During the design calculations, both scenarios of the tank being filled with water at no pressure and under pressure were taken into account; if everything passes, there should be no issues during the pressure test. As for the heat treatment process, temporary supports can be added.