Should it be classified?
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Just received an order: Diesel alkaline cleaning tank: design pressure of 1.6 MPA, design temperature of 60°C; medium: diesel, water, alkali； The volume is 40 cubic meters. The user specified in the provided conditions that the container should be classified as a Class 2 pressure vessel and that heat treatment be carried out. I think that container is sufficient for this purpose, as the boiling point of diesel is between 180 and 370°C, and no heat treatment is required. I appreciate your advice.
It should be classified as category two; you haven’t taken into account future conditions such as steam purging, nor the stress corrosion caused by alkaline solutions, which is why heat treatment is necessary.
The boiling point of diesel mentioned by the poster is 180–370°C; I wonder if this refers to the boiling point at a design pressure of 1.6 MPa According to the regulatory requirements, if the maximum temperature of the primary medium in the container is below the standard boiling point of a liquid, and the gas space (non-transient) is 0.025 cubic meters or more, classification is still required. Regarding heat treatment, since alkali solutions are present in the medium, stress corrosion can occur in carbon steel and low-alloy steel containers; therefore, heat treatment is necessary.
Replying to posts 2 and 4: the operating pressure of this container is 1. 5MPA, with a boiling point of 180–370 at standard conditions℃
Since the boiling point is already so high at such low pressures, it should be even higher at 1.5 Mpa
Did the original poster leave out another parameter? It’s the filling coefficient.
The diesel storage tank has a gas space, and the volume of this gas space is certainly greater than 0.025 cubic meters; therefore it should be classified as category II. As for heat treatment, it depends on the proportion of the alkaline solution, as well as whether it meets the upper temperature limit specified in the standards. Aside: The designer’s basic principle is to have rules to follow and guidelines to adhere to in order to protect themselves.
Heat treatment can be carried out according to the user’s requirements； Diesel is a volatile, flammable, and explosive substance; it is correct to classify it as a Class II container
Is steam purging classified by steam pressure or by operating pressure?
It is probably mainly due to considerations regarding the gas-phase space during operation. Additionally, a design pressure of 1.6 MPa falls under medium pressure, so it is classified as a Class 2 pressure vessel. What should be considered in heat treatment is the cause of alkaline embrittlement.