Steel grades
Steel grades to classify various steels by their composition and physical properties have been developed by a number of standards organizations.
Steel grades standards by country
- For alloys in general, unified numbering system of ASTM International and the Society of Automotive Engineers.
- American steel grades : AISI/SAE steel grades standard
- British Standards
- International Organization for Standardization ISO/TS 4949:2003
- European standards - EN 10027
- Japanese steel grades : Japanese Industrial Standards standard and NK standard
- Germany steel grades : DIN standard
- China steel grades : GB standard
- Czech steel grades : ČSN standard
- Russia steel grades : GOST standard
- Spain steel grades : UNE standard
- France steel grades : AFNOR standard
- Italy steel grades : UNI standard
- Sweden steel grades : SIS standard
- Norway steel grades : DNV standard
European standard steel grades
European standard steel grade names fall into two categories:- Steel specified by purpose of use and mechanical properties.
- Steel specified by chemical composition.
Category 1
Basic grade designations for category 1 steels consist of a single letter then a number signifying the mechanical property dictated in the standard for that application designation. For some application designations another letter is included before the property value, this number is used to indicate any special requirements or conditions. These additional letters and values depend entirely on the application of the steel and are specified in the standard and far too numerous to mention here.The next set of 3 digits gives the steel's minimum yield strength. So S355 has a minimum yield strength of 355 MPa for the smallest thickness range covered by the relevant standard – i.e. EN10025.
Below is a table indicating the most common application codes.
| Application symbol | Meaning | Mechanical Property | Details |
| S | Structural steel | Minimum Yield Strength | |
| P | Steel for pressure lines and vessels | Minimum Yield Strength | |
| L | Steel for pipe and tube | Minimum Yield Strength | |
| E | Engineering steels | Minimum Yield Strength | |
| B | Steel for reinforced concrete | Characteristic Yield Case | |
| R | Steel for rail use | Minimum Yield Case | |
| H | High Tensile Strength Flat products | Minimum Yield Case | If followed by T then the given mechanical property is minimum tensile strength |
| D | Flat Products for Cold Forming | Followed by C, D or X and two numbers characterising steel | |
| T | Tinmill Products | Nominal Yield Case | |
| M | Electrical Steel | Number = 100 × specific loss in W/kg Number = 100 × nom thick in mm Letter for type of product |
Additional symbols
In addition to the above category codes there are symbols that can be added to the grade code to identify any additional compositional requirements, delivery conditions, mechanical properties, &c. These values depend solely on the type/application code given in the first part of the code and are so numerous as to be impossible to indicate here. Additional symbols are separated from the main code by the plus sign.The most common additional symbols are the impact and temperature codes for structural steels, category 1 - Sxxx.
Delivery condition codes are also relatively common, the most common being:
| Code | Condition |
| A | Annealed |
| QT | Quenched and tempered |
| N | Normalised |
| SR | Stress relieved |
| C | Cold worked |
| U | Untreated |
Electrical steel type of product letters :
| Code | Maximum specific loss expressed for magnetic induction | Type of product |
| A | 1.5 T @50 Hz | non oriented |
| D | " | non-alloy semi-finished |
| E | " | alloy semi-finished |
| K | " | non-alloy and alloy electrical steel sheet/strip in the semi-processed state |
| N | " | for normal grain oriented products |
| P | 1.7 T @50 Hz | high permeability grain oriented |
| S | " | conventional grain oriented |
European standard steel number
In addition to the descriptive steel grade naming system indicated above, within EN 10027-2 is defined a system for creating unique steel grade numbers. While less descriptive and intuitive than the grand names they are easier to tabulate and use in data processing applications.The number is in the following format: x.yyzz
Where x is the material type, yy is the steel group number and zz is a sequential number designated by the certifying body, the number in brackets being unused but reserved for later use.
The steel groups are indicated below:
The current certification body is the VDEh in Düsseldorf, Germany.
Comparisons
Below is a table comparing steel grades from different grading systems.American Petroleum Institute (API) steel grades
Color coding
In order to clearly distinguish the steel grade, tubing, casing and its coupling should be painted with color codes respectively. Color bands should be painted on body longer than 600mm to either end. The whole outer-body of the coupling needs to be painted color and then color codes| Steel Grade | Coupling | Tubular Body | |
| API Tubing and Casing | H40 | - | None or black band at the manufacturer's option |
| API Tubing and Casing | J55 | all green. | one green band |
| API Tubing and Casing | K55 | all green | two green bands |
| API Tubing and Casing | N80-1 | all red | one red band |
| API Tubing and Casing | N80-Q | all red + one green band | one red band + one green band |
| API Tubing and Casing | L80-1 | all red + one brown band | one red band + one brown band |
| API Tubing and Casing | L80-9Cr | colorless + two yellow bands | one red band + one brown band + two yellow bands |
| API Tubing and Casing | L80-13Cr | colorless + one yellow band | one red band + one brown band + one yellow band |
| API Tubing and Casing | C90-1 | all purple | one purple band |
| API Tubing and Casing | T95-1 | all silver | one silver band |
| API Tubing and Casing | C110 | all white + two brown bands | one white band + two brown bands |
| API Tubing and Casing | P110 | all white | one white band |
| API Tubing and Casing | Q125 | all orange | one orange band |
API 5B and 5CT provide various steel grades and color codes of each grade, offering detailed and overall information of casing and tubing, which help you clearly pick out the most suitable products for different well application.