| Level | Degree | Model |
| G1 | Mild | The environment is sufficiently controlled that corrosion is not a factor affecting equipment reliability |
| G2 | Moderate | The impact of corrosion in the environment can be measured and corrosion may be a factor affecting the reliability of equipment |
| G3 | Harsh | The possibility of corrosion in the environment is very high. After further evaluation of the severity of the environment. |
| GX | Severe | Only specially designed equipment can survive in such an environment. The technical specification of this class of equipment is a point of discussion between the customer and the supplier . |
| Concentration Level | G1 | G2 | G3 | G4 |
| Concentration Level | < 300 | < 1,000 | < 2,000 | ≥ 2,000 |
| Siliver coupon reaction rate (Å) | < 200 | < 1,000 | < 2,000 | ≥ 2,000 |
| Common gas type | Common gas concentration (ppb) | |||
| (H²S) | <3 | <10 | <50 | ≥50 |
| (SO²) | <10 | <100 | <300 | ≥300 |
| (Cl²) | <1 | <2 | <10 | ≥10 |
| (NO²) | <50 | <125 | <1,250 | ≥1,250 |
| (HF) | <1 | <2 | <10 | ≥10 |
| (NH³) | <500 | <1,000 | <25,000 | ≥25,000 |
| (O³) | <2 | <25 | <100 | ≥100 |
