Selection of process parameters for tower equipment, classification, modification – comprehensive issues
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Basic information: The operating pressure of the tower equipment is 0.09 Mpa, while the design pressure is 1 Mpa. It was designed and manufactured in accordance with GB150-2011; the equipment does not fall into any specific category, and no approval was sought from the special inspection authority； After the equipment was installed in place (but not put into use), when the safety valve installed on the pipeline connected to the equipment (with an opening pressure of 0.2 Mpa) was submitted for inspection, the Special Equipment Inspection Institute raised concerns, arguing that this equipment should be treated as special equipment (requiring an increase in the operating pressure specified in the drawings), or that the opening pressure of the safety valve should be reduced to below 0.1 Mpa ； I have a few questions, and I would be grateful if the experts and professionals here could provide their guidance: 1. GB150’s definition of operating pressure: the highest pressure that may be reached at the top of the container under normal operating conditions ； “What does “normal conditions” mean, and are accident or fire scenarios included? Is the working pressure of 0.09 Mpa indicated on the current drawings reasonable from the perspective of GB150? 2. If the operating pressure is defined as 0.1 MPa or higher, it falls under the category of pressure vessels; may the owner increase the operating pressure of the equipment on their own for reasons such as efficiency, within the limits below the design pressure, during operation or after a three-year overhaul? Does this operation fall under the category of pressure vessel modifications? According to Article 5.2.1 of TSG21-2016, the definition of pressure vessel modification is “......changing the operating parameters of the pressure vessel”; a literal interpretation suggests that modification procedures are required ； 3. Currently, the opening pressure of the safety valve cannot be adjusted due to process requirements; if this equipment were classified as a device of the above type, what would be an appropriate working pressure?
In my opinion, what the Special Inspection Agency proposes is unreasonable; if the working pressure increases, then according to the agency’s logic, it will need to keep increasing further, since the pressure of the safety valve is higher than the working pressure
This device should not be treated as a special equipment, as no supervision and inspection were carried out during its manufacture. The setting pressure of the safety valve should be reduced.
The process cannot reduce the set pressure of the safety valve; does the equipment need to be taken apart and sent back to the factory?
The manufacturing process cannot reduce the set pressure of the safety valve; it must be redesigned and manufactured in accordance with the requirements for pressure vessels
According to GB150, the working pressure is the highest pressure that may be reached at the top of the vessel under normal operating conditions； Under normal operating conditions, I understand it should be in a stable operational state ； The opening of the safety valve (in cases of accidents, fires, etc.) should not be considered normal operating conditions, and it is due to instantaneous pressure ； I’m not sure if the above understanding is correct
The tower is equipped with internal components, and removing them is very costly； Redesign: Adjust the working pressure and classify it as a higher-tier device; this is relatively easy ； Remanufacturing: The material is a non-ferrous metal, and the equipment itself was designed for use under 150 pressure. This manufacturer follows standard procedures in all aspects of its operations; I think what’s needed is simply to add requirements for supervision during the inspection process. Are the inspection points that must be witnessed during this process limited to the water pressure test only?
It is relatively difficult to address this situation through the supervision by the Special Inspection Agency.