28 Chrome (UNS N08028), or Alloy 28, is a cold hardened nickel-based alloy intended for corrosion resistance in highly sour (H2S) environments with moderate chloride content, requiring high strength up to 350°F.
28 Chrome offers increased resistance to the effects of H2S relative to stainless steels allowing its use as downhole tubular components, packers, and other subsurface equipment in sour wells with high-pressure and high-temperature (HPHT) conditions and Acid Gas Injection (AGI) wells. In addition, it has a high resistance to pitting and crevice corrosion in the presence of chlorides. However, all environmental factors, including H2S, CO2 , temperature, pH, and chloride concentration, should be considered before final material selection.
The alloy is classified in MR0175/ISO15156 as a type 4c alloy, with no restrictions to a partial pressure of H2S below 270°F and resistant to 200 psi H2S at 350°F.
26 - 28
29.5 - 32.5
3 - 4
0.6 - 1.4
Made by electric furnace process or blast furnace followed by Vacuum Oxygen Decarburization (VOD) process or Argon Oxygen Decarburization (AOD) Process
Manufactured by traditional tube manufacturing processes, High strength tubulars should be furnished in cold worked condition
Solution Annealing Process before final cold drawing
Specified Mechanical Properties
API 5CRA / ISO 13680 Group 3 Category 27-31-4
Yield Strength ksi
Tensile Strength ksi
NACE MR0175/ISO 15156 H2S Sour Service Limits
Table A.14 Type 4c
No limit ≤ 270°F, Refer to table for temperatures up to 450°F
140 Grade not recommended for sour service
*Non-standard mechanical properties and grades are made available upon agreement.