Chemical composition and mechanical properties of API 5L sour service pipe
Last article we know what is sour service pipe,today let’s see the chemical composition and mechanical properties of API 5L sour service pipe.
API 5L Sour Service pipe Chemical Composition
1). C and carbon equivalent effect to sour pipe
C and carbon equivalent: With the mass fraction of carbon increases, the HIC sensitivity increases. The reduction of carbon and carbon equivalent can improve the H2S corrosion resistance of pipeline steel. And it will generate the harmful martensite formulas, which is very sensitive to H bubbles for the hot rolled steel.
2). P element for sour pipe
The P element is an easy to segregation element, so the increase of phosphorus mass fraction will lead to the increase of banded structure, thus increasing the sensitivity of the steel HIC.
3). S element effect for sour pipe
S element can promote the occurrence of HIC, the higher the sulfur content of the pipe body material, the easier to produce HIC. In addition, the anti – SSC performance of the pipes with high sulfur content is poor.
4). Mn element
In order to ensure the carbon content in high grade pipeline steel, manganese is usually used to improve its strength. The influence of manganese on HIC resistance of pipeline steel is mainly divided into three kinds:
1.Hot rolled line pipe steel with carbon content of 0.05 % ~ 0. 15 %
When the manganese content is 1. 0 %, the HIC sensitivity will increase abruptly:
- For the quenched and tempered line pipe steel
When the manganese content reaches 1.6 %, the hic resistance of the steel is not significantly affected by the manganese.
- In case carbon content is less than 0.02 %
If carbon less 0.02%, even if the manganese content exceeds 2.0%, the pipe still has good HIC resistance.
- Hardness requirement of sour service pipe
The hardness of the sour service pipe is strict, because the hardness value has a great influence on HIC. The results show that in low and medium strength steels, the higher the material strength, the greater the hardness, the stronger the HIC sensitivity.
- Corrosion test
In API 5L for sour service pipe, the hardness value of the base metal, weld and hot zone should not exceed 250 HV10. The hardness of the sour service pipe is more strict, because the hardness value has a greater impact on HIC. The research shows that the higher the material strength, the greater the hardness, the stronger the HIC sensitivity in low and medium strength steel.
Mechanical properties of API 5L pipe for sour service
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