The American Petroleum Institute (API) is a trade organization associated with the oil and natural gas industries. Welding standards issued by this organization are usually limited to welding for the oil and gas industry. Some of the more common welding work involves guidelines for piping and vessels under pressure.

The API welding code is lengthy and included below is a portion of the

API 570 Piping Inspection Code- This code covers the inspection, repair, alteration, and rerating of in-service piping systems.

  • API 570 was developed for the petroleum refining and chemical process industries but may be used, where practical, for any piping system. It is intended for use by organizations that maintain or have access to an authorized inspection agency, a repair organization, and technically qualified piping engineers, inspectors, and examiners, all as defined in Section 3.
  • API 620 This code lists the requirements for Design and Construction of Large, Welded, Low Pressure Tanks. This code applies to carbon steel above ground, including flat bottom tanks, that have a single vertical axis of revolution. The tanks described in this standard are designed for metal temperatures not greater than 250°F and with pressures in their gas or vapor spaces not more than 15 psi.
  • API 650 Welded Steel Tanks for Oil Storage. This standard covers material, design, fabrication, erection, and testing requirements for vertical, cylindrical, aboveground, closed and open-top, welded steel storage tanks in various sizes and capacities for internal pressures approximating atmospheric pressure (internal pressure not exceeding the weight of the roof plates), but a higher internal pressure is permitted when additional requirements are met. This standard applies only to tanks whose entire bottom is uniformly supported and to tanks in non-refrigerated service that have a maximum operating temperature of 90°C (200°F).
  • API 653 Tank Inspection, Repair, Alteration, and Reconstruction. This standard covers carbon and low alloy steel tanks built to API Standard 650 and its predecessor API Specification 12C. API 653 provides minimum requirements for maintaining the integrity of welded or riveted, atmospheric pressure, aboveground storage tanks after they have been placed in service. It covers the maintenance inspection, repair, alteration, relocation, and reconstruction of such tanks. The scope of this publication is limited to the tank foundation, bottom, shell, structure, roof, attached appurtenances, and nozzles to the face of the first flange, first threaded joint, or first welding-end connection. This standard employs the principles of API 650; however, storage tank owner/operators may apply this standard to any steel tank constructed in accordance with a tank specification.
  • API 1104 Welding of Pipelines and Related Facilities. This standard covers the gas and arc welding of butt, fillet, and socket welds in carbon and low-alloy steel piping used in the compression, pumping, and transmission of crude petroleum, petroleum products, fuel gases, carbon dioxide, and nitrogen, and where applicable, covers welding on distribution systems. It applies to both new construction and in-service welding. The welding may be done by a shielded metal-arc welding, submerged arc welding, gas tungsten-arc welding, gas metal-arc welding, flux-cored arc welding, plasma arc welding, oxyacetylene welding, or flash butt welding process or by a combination of these processes using a manual, semi-automatic, or automatic welding technique or a combination of these techniques, The welds may be produced by position or roll welding or by a combination of position and roll welding. This standard also covers the procedures for radiographic, magnetic particle, liquid penetrant, and ultrasonic testing as well as the acceptance standards to be applied to production welds tested to destruction or inspected by radiographic, magnetic particle, liquid penetrant, ultrasonic, and visual testing methods.