API RP 572-2009 pdf download.Inspection Practices for? Pressure Vessels.
3.1.20 on-stream A condition whereby a pressure vessel has not been prepared for internal inspection and may be in service. 3.1.21 owner-user An owner or user of pressure vessels who exercises control over the operation, engineering, inspection, repair, alteration, testing, and rerating of those pressure vessels. 3.1.22 pressure design thickness Minimum wall thickness needed to hold design pressure at the design temperature as determined using the rating code formula. It does not include thickness for structural loads, corrosion allowance or mill tolerances. 3.1.23 pressure vessel A container designed to withstand internal or external pressure. This pressure may be imposed by an external source, by the application of heat from a direct or indirect source, or by any combination thereof. This definition includes heat exchangers, air-coolers, unfired steam generators and other vapor-generating vessels which use heat from the operation of a processing system or other indirect heat source. 3.1.24 pressure vessel engineer One or more persons or organizations acceptable to the owner-user that are knowledgeable and experienced in the engineering disciplines associated with evaluating mechanical and material characteristics that affect the integrity and reliability of pressure vessels. The pressure vessel engineer, by consulting with appropriate specialists, should be regarded as a composite of all entities necessary to properly address a technical requirement. 3.1.25 repair The work necessary to restore a vessel to a condition suitable for safe operation at the design conditions. If any of the restorative work results in a change to the design temperature, MDMT, or MAWP, the work shall be considered an alteration and the requirements for rerating shall be satisfied. Any welding, cutting, or grinding operation on a pressure-containing component not specifically considered an alteration is considered a repair.
4 Introduction to Pressure Vessels 4.1 General A pressure vessel is a container designed to withstand internal or external pressure. The pressure vessels may have been constructed in accordance with ASME BPVC Section VIII, other recognized pressure vessel codes, or as approved by the jurisdiction. These codes typically limit design basis to an external or internal operating pressure no less than 15 lbf/in. 2 (103 kPa). However, this RP also includes vessels that operate at lower pressures. External pressure on a vessel can be caused by an internal vacuum or by fluid pressure between an outer jacket and the vessel wall. Vessels subject to external pressure are usually inspected in the same manner as those subject to internal pressure. Columns, towers, drums, reactors, heat exchangers, condensers, air coolers, bullets, spheres, and accumulators are common types of industry pressure vessels. [See Annex A for an introduction to exchangers. Storage vessels subject to internal pressures up to 15 lbf/in. 2 (103 kPa) are covered in API 575.] Pressure vessels are designed in various shapes. They may be cylindrical (with flat, conical, toriconical, torispherical, semi-ellipsoidal, or hemispherical heads), spherical, spheroidal, boxed (with flat rectangular or square plate heads, such as those used for the headers of air-cooled exchangers), or lobed. They may be of modular construction.
4.2 Methods of Construction Prior to the development of welding, riveting was the most common method of construction. Seams were either lapped and riveted, or butted with butt straps and then riveted. To prevent leakage, the edges of the seams and rivet heads were caulked. At high temperatures, it was difficult to keep this caulking tight. After the technique of welding was developed, a light bead of weld was applied to the caulking edges. Although some vessels of this type can still be found in older refineries, this method of construction is seldom used today. Today, several different methods are used to construct pressure vessels. Most pressure vessels are constructed with welded joints. Shell rings are usually made by rolling plate at either elevated or ambient temperature. The cylinder is formed by welding the ends of the rolled plate together. This yields a cylinder with a longitudinal weld. Hot forging is another method of making cylindrical vessels. Some vessel manufacturers hot forge cylindrical shell rings for high-pressure, heavy-wall vessels such as those used for hydrotreater or hydrocracker reactors. This method does not produce a longitudinal seam in the cylinder. In the multilayer method, the cylindrical section is made up of a number of thin concentric cylinders fabricated together, one over the other, until the desired thickness is obtained. Multilayer construction is sometimes used for heavy-wall reactors and vessels subject to high pressure.