API RP 572:2009 pdf download

API RP 572:2009 pdf download.lnspection Practices for Pressure Vessels.
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.
4.3 Materials of Construction
Carbon steel is the most common material used to construct pressure vessels. For special purposes, a suitable austenitic or femtic alloy, Alloy 400, nickel, titanium, high-nickel alloys or aluminum may be used. Copper and copper alloys (except Alloy 400) are seldom used in refinery vessels but are common with heat exchanger tubes and may be found in petrochemical plant vessels.
Materials used to constwct the various parts of heat exchangers are selected to safely handle the service and the heat load required. Materials that will most economically resist the type of corrosion expected are selected.
Exchanger shells are usually made of carbon steel but may be made of a corrosion-resistant alloy or dad with a corrosion-resistant material. Exchanger channels and baffles are made of carbon steel or a suitable corrosion- resistant alloy material, usually similar to the material of the tubes.
Tubes for exchanger bundles may be a variety of materials. Where water is used as a cooling or condensing medium, they are generally made of copper based alloys or steel. In water applications where copper alloys or steels will not provide sufficient corrosion protection, higher alloy materials may be used such as duplex stainless steel, or the tube ID may be coated (baked epoxy or similar). Titanium may be used in seawater applications. Where the exchange is between two different hydrocarbons, the tubes may be made of steel or a suitable corrosion-resistant alloy. Tubes, consisting of an inner layer of one material and an outer layer of a different material (bimetallic), may in some cases be required to resist two different corrosive mediums.
Tubesheets for exchanger bundles are made of a variety of materials. Where water is the cooling or condensing medium, they are usually made of admiralty brass or steel, but may also be constructed of high-alloy steels (clad or solid). Titanium may be used in seawater applications. Where the exchange of heat is between two hydrocarbons, the tubesheets may be composed of steel or a suitable corrosion-resistant alloy. In some cases it may be necessary to face one side of the tubesheet with a material different from that facing the other to resist two different corrosive mediums.
If carbon steel would not resist the corrosion or erosion expected or would cause contamination of the product, vessels may be lined with other metals or nonmetals.