API 5CRA specifies corrosion resistant alloy seamless tubes for casing, tubing and coupling stock. It is the specification behind the CRA tubulars used in sour and CO2-bearing wells, and it is deliberately built around the environment rather than around the alloy alone.
How the specification is organised
Grades are designated by a combination of alloy type and minimum yield strength, and each combination has a defined set of mechanical properties and delivery conditions. That structure exists because the same alloy at two strength levels behaves very differently in sour service.
| Family | Typical designation | Used for |
|---|---|---|
| 13 % Cr | 13Cr-80 / 13Cr-95 | Sweet wells with CO2, moderate temperature |
| Super 13 % Cr | S13Cr-110 | Higher CO2 and chloride, still low H2S |
| 22 % Cr duplex | 22Cr-110 | Sour with chlorides, moderate temperature |
| 25 % Cr super duplex | 25Cr-125 | More severe sour and chloride service |
The environmental part is the point
5CRA does not say a grade is suitable for a well. Suitability is set by ISO 15156 / NACE MR0175 against H2S partial pressure, pH and temperature, and 5CRA references those limits rather than replacing them. A tube can meet 5CRA mechanically and still be prohibited for the environment it is ordered for.
What to put on the purchase order
- Grade designation with strength level
- Environment: H2S partial pressure, CO2, chloride content, temperature and pH
- Connection type and whether coupling stock is included
- NDT and pressure test requirements
- Traceability and third-party inspection, if required
Download the standard
API 5CRA — Corrosion resistant alloy seamless tubes for casing, tubing and coupling stock (PDF)
Related reading
- ISO 15156 / NACE MR0175 — the standard that sets the environmental limits.
- F55 super duplex — the grade behind many 25Cr tubulars.
- Stainless steel in oil and gas — choosing by H2S severity.
