Manhole refers to the opening structure used for personnel to access equipment for installation, maintenance and inspection. It is mainly composed of short tube joint (or short pipe), flange and manhole cover with handle. From the perspective of inspection, the number of manholes required to be opened for pressure vessels and their smaller size are shown in "inspection holes". Manhole materials are carbon steel and stainless steel. According to the pressure situation, the manhole can be divided into atmospheric pressure manhole and pressure manhole; according to the shape of manhole, it can be divided into round manhole, elliptical manhole and rectangular manhole; the rectangular manhole is only suitable for atmospheric pressure equipment; according to the installation position, the manhole can be divided into horizontal and vertical installation manhole; the manhole cover is fixed by rotating cover and hanging cover; the opening speed of manhole is ordinary and quick opening, and the structure and size of manhole are generally standardized, which can be referred to Relevant manual selection or design.
