【Q&A Question 135】2016.09.02

Prevent thermal expansion and contraction, bolt loosening, and flange leakage.

Since the thermal conductivity and the coefficient of thermal expansion are different, this prevents the components from loosening due to thermal expansion and contraction.

After maintenance or at the time of initial operation, the bolts of the equipment’s pipelines are replaced or tightened/loosened, and this is done at normal temperature, that is, at low temperatures; whereas during the equipment’s normal operation, these tasks are carried out at higher temperatures. As the temperature rises, pipelines, flanges, and bolts undergo thermal expansion. The coefficient of thermal expansion for bolts is different from that of the equipment or pipeline flanges; as a result, some of the bolts used to secure the flanges may loosen, or the seal between the flanges may fail due to insufficient tightening force caused by thermal expansion. To prevent leaks and ensure the safe operation of the device, it is necessary to tighten it thermally

Bolts, or certain flanges, may loosen or deform when exposed to uneven heat at high temperatures; without proper tightening, leaks can occur

After maintenance or at the time of initial operation, the bolts of the equipment’s pipelines are replaced or tightened/loosened, and this is done at normal temperature, that is, at low temperatures; whereas during the equipment’s normal operation, these tasks are carried out at higher temperatures. As the temperature rises, pipelines, flanges, and bolts undergo thermal expansion. The coefficient of thermal expansion for bolts is different from that of the equipment or pipeline flanges; as a result, some of the bolts used to secure the flanges may loosen, or the seal between the flanges may fail due to insufficient tightening force caused by thermal expansion. To prevent leaks and ensure the safe operation of the device, heat tightening is necessary; it is recommended to carry out this process at a temperature of 250 degrees ； At low heat-setting temperatures, the metal’s coefficient of expansion is small; however, if the temperature is too high, the contracting force during heat setting in the cold state becomes excessive.

Before starting up, the pipeline bolts that are removed, installed, or replaced are tightened at room temperature, whereas during normal operation of the equipment, this is done at higher temperatures. As the temperature rises, pipelines, flanges, and bolts undergo thermal expansion. The coefficient of thermal expansion for bolts is different from that of the equipment or pipeline flanges; as a result, some of the bolts used to secure the flanges may loosen, or the flange seals may leak due to insufficient tightening force caused by thermal expansion. To ensure no leaks and the safe operation of the equipment, heat tightening is necessary; this is carried out when the bottom temperature of each tower in the distillation system reaches 205 degrees, during the operation of the hot oil.

Prevent leaks caused by a decrease in flange tightening pressure as temperature rises

After maintenance or at the time of initial operation, the bolts of the equipment’s pipelines are replaced or tightened/loosened, and this is done at normal temperature, that is, at low temperatures; whereas during the equipment’s normal operation, these tasks are carried out at higher temperatures. As the temperature rises, pipelines, flanges, and bolts undergo thermal expansion. The coefficient of thermal expansion for bolts is different from that of the equipment or pipeline flanges; as a result, some of the bolts used to secure the flanges may loosen, or the seal between the flanges may fail due to insufficient tightening force caused by thermal expansion. To prevent leaks and ensure the safe operation of the device, heat tightening is necessary; it is recommended to carry out this process at a temperature of 250 degrees ； At low heat-setting temperatures, the metal’s coefficient of expansion is small; however, if the temperature is too high, the contracting force during heat setting in the cold state becomes excessive. Thermal tightening is only required in the original state and when components are replaced or removed; it is not necessary during normal start-up and shutdown operations ； It is recommended to perform thermal tightening on key areas when resuming operation after an emergency shutdown, especially when there are significant fluctuations in temperature and pressure