Gaskets are mechanical seals, usually formed like a ring and used for sealing of flange joints.
In general, gaskets should not be reused.Various types of gaskets are available depending upon their construction, materials, and features.
The following are the type of gaskets commonly used: Non-Metallic Gaskets (ASME B 16.21) Spiral-Wound Gaskets (ASME B 16.20) Ring Joint Gaskets (ASME B 16.20) Non-Metallic Gaskets are used with flat face or raised face flanges.
They are available with an inner ring and outer ring, which is also known as the cantering ring.Ring Joint Gaskets are used with Ring Type Joint (RTJ) flanges.
They are available in octagonal or oval cross sections. A very high surface stress is developed between an RTJ gasket and the flange groove when RTJ is bolted up in a flange.
This leads to plastic deformation of the gasket.
Thus, the hardness of the gasket is kept less than the hardness of the groove to achieve coining i.e.bringing two metal surfaces of different hardness so tightly together that the softer surface deforms to match harder surface exactly in shape and finish.
This was a source of lead-related health problems in the years before the health hazards of ingesting lead were fully understood; among these were stillbirths and high rates of infant mortality.
Lead water pipes were still widely used in the early 20th century, and remain in many households.
The pipes were hollowed-out logs, which were tapered at the end with a small hole in which the water would pass through.The multiple pipes were then sealed together with hot animal fat.
They were often used in Montreal and Boston in the 1800s, and built-up wooden tubes were widely used in the USA during the 20th century.These pipes, used in place of corrugated iron or reinforced concrete pipes, were made of sections cut from short lengths of wood. Locking of adjacent rings with hardwood dowel pins produced a flexible structure.
About 100,000 feet of these wooden pipes were installed during WW2 in drainage culverts, storm sewers and conduits, under highways and at army camps, naval stations, airfields and ordnance plants. Cast iron and ductile iron pipe was long a lower-cost alternative to copper, before the advent of durable plastic materials but special non-conductive fittings must be used where transitions are to be made to other metallic pipes, except for terminal fittings, in order to avoid corrosion owing to electrochemical reactions between dissimilar metals (see galvanic cell).Źródło: https://en.wikipedia.org/wiki/Water_pipe