The issue of the minimum operating temperature in hydrogenated dewaxing reactors: how to prevent hydrogen embrittlement and bulging during normal production
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During summer production, the demulsification reactor was removed (by connecting a bypass line), which prevented any material from passing through; as a result, the temperature gradually decreased. However, since it was a hydrogen-rich environment, the equipment specialists were concerned that this could lead to hydrogen-induced cracking. Yet they were unable to specify a minimum operating temperature for the reactor. 1. What determines the general minimum operating temperature? Hydrogen partial pressure? 2. The operating pressure is approximately 4.0 MPa (pressure at the reactor inlet); what is the corresponding lowest operating temperature? Manager Discussion Group
This is usually included in the completion documents. Which discipline is concerned with the minimum operating temperature for hydrogen-induced cracking? Mechanics? Equipment? Process?
The lowest operating temperature corresponding to an operating pressure of about 4.0 MPa
When the wall temperature is 93 degrees, the pressure does not exceed 1/4 of the normal pressure
According to the technical Q&A on hydrocracking units, the material commonly used for the reactors in such units is 2 1/4Cr-1Mo. Since chromium-molybdenum steel becomes brittle when operated at temperatures between 370 and 575°C for extended periods, this type of steel is prone to brittle fracture at temperatures below 121°C. Therefore, it is generally recommended that when the temperature is below 121°C, the pressure in equipment made of 21/4Cr1Mo and 3Cr1Mo steels should be kept within a range such that the resulting stress does not exceed 20% of the material’s yield strength. However, considering the difference between the temperature inside the reactor and the temperature of its outer wall, some systems set this temperature at 135°C. In addition, in areas where there are significantly high residual stresses or mechanical loading stresses, close monitoring and more stringent inspections should be carried out cautiously. To ensure safety, it is generally required that when the temperature is below 135°C, the pressure must not exceed 1/4 of the total pressure. When starting up the reactor, temperature should be increased first followed by pressure; during shutdown, pressure should be reduced first before temperature is lowered. From a mechanical design perspective, the cooling rate should not exceed 25°C/h, and the reactor temperature must not be lowered to below 135°C until the pressure drops to 1/4 of the total pressure. These measures are beneficial for reducing equipment stress, minimizing the tendency of the surfacing layer to peel off, and preventing damage caused by temper brittleness. To prevent the stainless steel surfacing layer of the reactor and the inner walls of the stainless steel process pipes from coming into contact with humid air during shutdown periods, thereby forming polysulfates with iron sulfide on the metal surface and causing stress corrosion cracking in the stainless steel, nitrogen protection measures for the equipment and pipelines, or alkaline neutralization and cleaning procedures, have been specified.
The operating temperature and pressure are determined based on the catalyst, and the selection of your reactor is also made accordingly; the equipment specifications will explain this to you
It doesn’t use the official process kit, right? There should be a hydrogen return pipeline along the way, with temperature control
The minimum operating temperature you mentioned is related to the material; in our reactors, when the pressure is greater than 2.0 MPa, the wall temperature of the reactor must be above 100°C.