About the Standard
Scope title: welded steel storage tanks
API 650 is a standard published by American Petroleum Institute (API). It publishes equipment, pipe and lubricant standards for the oil and natural gas industry.
See the other 11 codes from APICoverage areas
Metal and Metallurgy Testing — What Does This Testing Field Cover?
The section below describes the field that code API 650 belongs to; it is not the text of the standard or the regime itself. The scope title of the code is given above, and technical requirements are shared at the quotation stage.
Metal and metallurgical testing determines the load a metal or a welded joint can carry, how it fails and what its internal structure looks like. The output of this family is often not about the product itself but about the identity of the MATERIAL: is the steel really of the declared grade, does the weld seam deliver the strength the design assumes, does the casting contain an unacceptable internal defect?
The practical importance of the field comes from the fact that a metal part rarely fails gradually. A plastic part deforms, ages, cracks and usually gives warning. A weld seam or a fastener, by contrast, often breaks without warning — especially where fatigue and brittle fracture are involved. That is why in fields such as pressure equipment, lifting gear, structural steel and pipelines, material testing is a requirement of REGULATION rather than of design.
The family brings together three groups of methods, and each answers a different question. Mechanical tests quantify how the material behaves under load. Non-destructive examination looks for defects without damaging the part. Metallography and chemical analysis explain why the material behaves the way it does — through grain structure, phase distribution, inclusion content and alloy composition.
The acceptance criterion for these tests almost never comes from the test standard, and this is the key to understanding the field. The test standard says how the measurement is to be made; the acceptable values come from the product standard, the material grade or the fabrication code. ISO 6892-1 tells you how to run a tensile test; EN 10025 tells you what yield strength that steel must deliver. When reading a report, the product standard it was assessed against is essential.
Sampling is an inseparable part of the result in this field. Two specimens taken from the same heat may give different values depending on the direction and location they were taken from; in rolled products, specimens parallel and perpendicular to the rolling direction produce different results. Product standards therefore also govern sampling location and orientation, and the report must document this.
Method groups in this field
Mechanical tests
Tensile, compression, bending, notch impact (Charpy), hardness (Brinell, Vickers, Rockwell), fatigue, creep and fracture toughness. These give the behaviour of the material under load in numerical form.
Non-destructive examination
Radiography, ultrasonic examination, penetrant, magnetic particle and visual examination. It looks for surface and internal defects without damaging the part and is an indispensable step in welded fabrication.
Metallography
Specimen preparation, etching and microscopic examination. Grain size, phase distribution, inclusion content, case depth and the weld heat-affected zone are assessed.
Chemical analysis
Alloy composition is verified by optical emission spectrometry and wet chemistry; confirmation of the material grade runs through this step.
Corrosion behaviour
Salt spray, pitting and crevice corrosion and intergranular corrosion tests. In stainless steels these can indicate the quality of the heat treatment.
Commonly confused in this field
- A material certificate (such as EN 10204 3.1) is not a test report; it is the manufacturer's declaration. In critical applications independent verification is carried out, and the two must not be confused.
- ASTM and ISO tensile tests measure the same quantities but use different specimen geometries; the results are not treated as directly equivalent, and whichever the specification calls for is the one applied.
- Conversion tables between hardness and strength are APPROXIMATE. Calculating yield strength from hardness is not sufficient evidence for material acceptance.
- In non-destructive examination, "no defect found" does not mean there is no defect; defects below the detection limit of the method may be present. The report must state the method applied and the sensitivity level.
- A weld seam passing does not show that the welder or the procedure is qualified; these are separate processes.
Which decisions these results support
- Verifying the material certificate and accepting incoming material
- Approving welded fabrication; welder and procedure qualification
- Manufacturing control of pressure equipment and structural components
- Failure analysis and determining the root cause of field damage
- Verifying heat treatment and surface treatment processes
Structure of the Code
- Published by
- API
- Serial number
- 650
- Part
- without partition
Codes in the library without release year is kept. The current version changes over time; If the year is specified in your specification, that version is taken as basis, if not specified, the most current version is applied.
Scope
Related Tests and Services
A separate test page based on this code has not yet been released. The code falls within the scope of the following test families.
Technical Requirements
Standard texts are copyright of the relevant organization; test condition, sample and acceptance criteria cannot be fitted here.
Technical requirements specific to your product, once we clarify the scope At offer stage shared in writing.
Relevant Product Groups and Legislation
This code is included in the standard tag of the product pages below.
These product pages carry notes for the following markets: European Union, United Kingdom, USA. Whether the standard is mandatory in the relevant market varies depending on the product group and the applicable legislation.
Regulations published with this code on the same product pages:
- 2006/42/ATMachinery DirectiveRisk assessment, essential health and safety requirements and a technical-file obligation.
- (EU) 2023/1230Machinery RegulationReplaces 2006/42/EC, mandatory on 20 January 2027 with no further transition period.
- 2014/35/EULVDElectrical safety under the Low Voltage Directive.
- 2014/30/EUEMCEmission and immunity are assessed together.
- 2014/68/EUPEDThe Pressure Equipment Directive for pressurised parts; the category is determined by pressure and volume.
- 2000/14/ATNoise EmissionSound-power-level declaration and marking for compressors used outdoors.
- (EU) 2024/573F-GasRefrigerant type, GWP value and leak-tightness obligations for systems containing a refrigerant.
- 2014/34/ABATEXEquipment and protective systems used in explosive atmospheres. The category and conformity route are determined by zone classification.
- (AB) 547/2012Ecodesign (water pumps)Ecodesign requirements for water pumps. Sets minimum efficiency index and product-information requirements.
- (AB) 2019/1781Ecodesign (electric motors)Efficiency class requirements for electric motors and variable-speed drives.
- (AT) 1935/2004Food Contact MaterialsGeneral requirements for equipment in contact with food; material conformity is required for valves in food lines.
- (AB) 2020/2184Drinking Water Contact ProductsHygiene requirements for materials in contact with water under the Drinking Water Directive.
Other Adoptions of the Same Number
This number is also published by other bodies. Adoptions may carry a national annex; the code named in your specification is the one required.
Related Standards
Frequently Asked Questions
Is this standard mandatory for my product?
Whether it is mandatory depends on the product group, the target market and the applicable legislation. Once you tell us your product and market, we clarify in writing whether this standard is required.
How long does the test process take?
Duration depends on the scope of the standard, the number of specimens and current capacity. The exact duration is shared, together with the specimen and scope details, at the quote stage.
Do you issue certification against this standard?
Which activity is carried out under which accreditation scope is separately confirmed at the application stage. Up-to-date scope information is published on our corporate page.
What happens if the standard I need is not here?
The library is based on a continuously growing inventory. If you cannot find the code you are looking for, you can send it through the quote form; we will assess the relevant scope and get back to you.