Seal leakage at the manway flange of the boiler drum

How would you describe this deformation? Are the inner and outer dimensions of the standard pad not suitable?

If the medium permits, try copper; it is relatively soft after annealing

Some use copper pads, and some leak: L

The sealing surface is on the inside, so the gasket must be larger than the sealing surface in order to deform and fit in

Metal wound gaskets can be customized; just inform the manufacturer.

Duplicate replies can be deleted by yourself.

Both flexible graphite composite sheets and toothed gaskets can be used

Who designed these plans? Must be crazy – the self-sealing manholes aren’t round; elliptical shapes are the standard. What if workers seal and weld it before putting the manhole cover inside? Then the cover won’t fit in at all !

This post was last edited by Grey Wolf_FMHHs on 2023-6-28 at 14:42. Asbestos gaskets are now prohibited; metal wound gaskets should be used instead. Analysis of the causes of failure in the sealing surface of the boiler drum. The manhole of the drum serves as an access point for inspecting and maintaining the drum; once the internal maintenance is completed, the manhole must be sealed. The degree of sealing of the manhole directly affects the water filling process of the boiler as well as its safe operation; therefore, ensuring proper sealing of the manhole is also an important aspect of maintenance work. Here is an analysis of the common factors that cause leakage at the sealing surface of the drum manway. 1.1 Improper use of the drum gasket (1) The gasket for the drum manhole is a key component that ensures a tight seal at this manhole. Steam drum gaskets with pressure and temperature ratings higher than those of the steam drum’s operating conditions should be used; the use of gaskets with lower ratings is strictly prohibited. Otherwise, during the boiler pressurization or startup process, as the temperature and pressure inside the steam drum increase, the gaskets with lower ratings will gradually fail, ultimately leading to leaks at the steam drum’s manholes and forcing the boiler to be shut down for maintenance. (2) The steam drum gasket used has defects, such as scratches, irregularities, cracks, and delamination on its working surface. As the pressure and temperature of the steam drum increase, these defects become weak points in the sealing surface, ultimately leading to leaks at the steam drum manway during boiler startup or operation, forcing the boiler to be shut down for maintenance. (3) The thickness deviation of the steam drum gasket used is large, resulting in a failure to provide proper sealing. There are two scenarios for such problems: first, the gasket is too thin, resulting in insufficient compression after sealing of the steam drum, and thus no sealing effect is achieved; second, the gasket is too thick, preventing the sealing surface of the steam drum’s manway from forming a proper interlocking seal with the sealing surface of the steam drum itself, again leading to no sealing effect. The above two situations can directly cause leakage at the manway during boiler pressurization or startup, forcing the boiler to stop operating. 1.2 Improper maintenance of the drum manhole (1) Leakage at the manhole is caused by improper installation of the gasket. Since the drum manhole is of the inward-opening sealing type, when the manhole is closed, its sealing surface is relatively smooth, which makes it impossible to secure the gasket. As a result, the gasket often shifts out of its proper sealing position, or it is not within the effective sealing range; consequently, the effective sealing performance is insufficient, leading to leakage at the drum manhole. (2) The surface finish on both sides of the seal surface of the drum manhole was insufficient; defects such as pitting, depressions, and mechanical damage were present. These issues were not properly addressed during maintenance, which led to leakage at the seal surface after the manhole was reinstalled. The end view of the steam drum is shown in Figure 1. (3) Insufficient bolt tension on the drum manway caused leakage at the sealing surface. There are two factors contributing to this issue: one is insufficient tightening force of the drum bolts themselves – during the boiler startup and pressure increase process, the bolts on the drum manway were not tightened thermally to a pressure range of 0.2–0.5 MPa. The other factor is the large thread clearance between the threads of the drum bolts and those at the bottom of the drum manway; as the boiler starts up, thermal expansion of the bolts further increases this thread clearance, and the insufficient tightening force between the thread bottoms and the bolts causes them to loosen, resulting in no pre-tightening force on the drum manway and thus leakage. 1.3 The sealing gasket of the drum manhole was not replaced in a timely manner. The sealing of the drum manhole is a type of static seal, which achieves its sealing effect under the force applied by the bolts securing the drum. During the startup or shutdown of the boiler, there is always a difference between the temperature of the drum wall and the temperature of the manholes. This temperature difference ultimately leads to relative displacement between the drum wall and the manholes. At the same time, the tightening force of the drum bolts can cause the gasket to stick to the drum wall or either side of the manway, resulting in slight damage to the sealing surface. If the drum gasket is not replaced in a timely manner, frequent starting and stopping of the boiler will lead to the failure of the sealing surface, ultimately causing leakage at the drum manway. 1.4 Common faults that occur during the operation of the drum include leakage at the welds of the connection fittings, cracks in the head, damage to the gasket of the manway, rusting of the manway bolts, short circuits in the steam-water flow caused by changes in the internal components of the drum, corrosion, scaling, malfunctioning expansion indicators, loosening or displacement of the steam-water separation device, accumulation of sludge, blockage of the chemical dosing pipes, and peeling of the insulation. 2. Measures for addressing leaks at the manhole doors: (1) The gasket used at the drum manhole door is a critical component for ensuring a tight seal; high-strength asbestos sheets or wound gaskets that are of higher quality and capable of withstanding higher pressure and temperature levels than those required for the drum should be used. Before use, the gasket should be checked to ensure it is flat and smooth, with no scratches or grooves; the inner and outer dimensions of the gasket must meet the sealing requirements for the drum manway, and its effective sealing width should be at least 20 mm. The thickness of the gasket used should be between 1.5 and 2.0 mm; it should neither be too thick nor too thin, as long as it meets the required compression amount for sealing. (2) The reinstallation process of the drum manhole door shall strictly comply with the \"Guidelines for Maintenance of Boiler Units in Thermal Power Plants.\" During maintenance, special attention should be paid to the manhole door: it should open and close smoothly without any sticking. The joint surface of the manhole door must be intact and smooth, and the door frame and door cover should be free of cracks, pitting, or mechanical damage. Any such defects must be addressed and corrected promptly. (3) Before entering the boiler drum, maintenance personnel should count and check the tools that need to be taken in along with the special work clothes. Before opening the manhole door, ensure that there is no residual pressure inside the boiler drum. After it is opened, a temporary manhole door should be installed; once the maintenance personnel have left the boiler drum, the temporary manhole door must be closed immediately, locked, and sealed with a special seal. The electrical equipment used inside the boiler drum must meet the requirements. The visible pipe openings in the lower half of the cylinder should be equipped with secure temporary sealing devices, and the pre-installed fixed sealing mesh covers should be inspected. (4) The steam-water separation device shall be tight and intact; the separator shall not be loose or tilted, and the joints shall remain flat and secure. The pins and fastening nuts on the separator shall not be loose or fallen off. All pipe socket holes, as well as the connection tubes for the water level gauge and pressure gauge, shall remain unobstructed, with no dirt accumulation or blockages on the inner walls. The horizontal deviation of the overflow threshold shall not exceed 0.5 mm/m, and the maximum overall horizontal deviation shall not exceed 4 mm. The inner walls of the boiler drum, along with the surfaces of its internal components and accessories, must be smooth, and the openings in the cleaning orifices and flow equalizing orifices shall not be blocked. (5) Inspect the longitudinal and circumferential seams on the inner and outer walls of the boiler drum, as well as the welds of the manway reinforcement rings and embedded components; inspect the fillet welds at the pipe seat ends of the concentrated downcomers, distributed downcomers, and other visible pipes. (6) Each time the drum manhole is opened, the bolts of the manhole and the threads of the bottom nuts should be measured and inspected; the threads must be free from wear and corrosion, and the bolt tension must meet the required standards. During boiler startup, the manhole bolts should be tightened again once the drum pressure reaches 0.3–0.5 MPa. (7) The reinstallation of the seal gasket for the drum manhole should be carried out by experienced maintenance personnel. During the process, it is necessary to first ensure that the seal gasket fits perfectly with the areas that need to be sealed by the manhole, and then the bolts should be pre-tightened. After pre-tightening, it is important to check that the gaps around the manhole are even and that the seal gasket is not skewed. Once everything is confirmed to be in order, the bolts of the manhole should be tightened evenly again until the required tension is achieved. (8) For boilers that are started and stopped frequently, the gasket replacement for the drum manhole should be scheduled regularly, taking into account the number of times the boiler is started and stopped. Power plants under certain conditions can shorten the replacement cycle for the gasket on the drum manway; under normal circumstances, it should be replaced every 3 years, while for boilers that are started and shut down frequently, this period can be appropriately reduced to 2 years.