Selection of materials for pipe fittings under hydrogen sulfide stress corrosion resistance

For the selection and evaluation of materials used in equipment designed and manufactured in accordance with the elastic design guidelines can be selected in accordance with ISO 15156-2 (GB/T20972.2) and ISO15156-3 (GB/T20972.3) or NACE_MR0175-2003 standards have been assessed and qualified materials, these standards have been limited to avoid the occurrence of stress corrosion Environmental conditions, only when meeting this qualification can be selected in accordance with the requirements of the corresponding specifications; such as not meeting these qualifications need to carry out HIC and SSC test to meet the requirements of the corresponding standards.

1. The material used must meet the requirements of NACEMR-0175/ISO 15156-2015
2. The hardness of the material should not exceed 22 HRC . (Among them: SA-105 does not exceed 187 HBW)
3. The measured tensile strength of the material is not more than 630 MPa, and the nominal yield strength under the standard is not more than 355 MPa
4. The use of vacuum degassing process or other alternative processes, for fine grain sedimentation steel
5. Materials should be normalized or normalized + tempered state supply
6. Material non-metallic inclusions A, B, C and D shall not exceed 2 levels, the total number shall not exceed 4.0 levels, test methods in accordance with ASTME45 or ISO4967.
7. Material in accordance with ASTM E112 for austenitic grain size testing, requiring an average grain size of 7 or finer.
8. Material ultrasonic testing requirements
9. Chemical composition restrictions.
   C ≤ 0.20% S ≤ 0.012% P ≤ 0.015% Ni <1.0% Mn ≤ 1.0% CE ≤ 0.43 Note: CE = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15
10. The material should meet the impact test requirements under MDMT
11. Material Z-directional tensile requirements (standard: SA-770 or EN10164 or GB/T5313 three specimens average ≥ 35%, individual values ≥ 25%,)
12. HIC test
    Specifications: NACE TM0284-2016 solution: A solution test time: 96h test evaluation: CLR ≤ 15% CTR ≤ 5% CSR ≤ 2% 13. SSC test specifications: NACE TM0177-2016 solution: A solution test time: 720h threshold stress: 80% AYS (the actual yield strength of the material)