Factors affecting the HIC performance of seamless steel pipes

Posted by zora li on September 19th, 2023

Factors affecting the HIC performance of seamless steel pipes

Seamless line pipes are mainly used to transport high-pressure oil and gas near the wellhead. With the deepening of oil and gas exploitation, there are more and more oil and gas wells with complex mining conditions and sulfur-containing environments, and the problem of hydrogen sulfide corrosion is becoming more and more serious. The development of sulfur-resistant seamless line pipes is urgent. The addition of Cu and Ni can improve the HIC performance of seamless line pipe materials, reduce the S content in steel, and reduce the sensitivity of hydrogen bubbling by spraying calcium silicon powder.

1 Test method
In accordance with the ISO3183 standard, the immersion method was used to smelt 7 furnaces of 1 ton steel ingots in the laboratory. After forging, perforating, pipe jacking, and stretching, the pipe is made, and a 20 mm × 100 mm × 5 mm plate or pipe thickness is cut from the steel pipe for testing. The sample is immersed in a standard solution, taken out after 96 hours, and the cross-section is rolled vertically to calculate three parameters (crack length ratio CLR, crack thickness ratio CTR, and crack sensitivity ratio CSR). Metallographic method. Comparison of susceptibility to hydrogen-induced cracking (HIC).

2 Factors affecting HIC performance

1) pH value. A large number of research results show that in the pH range of 1-6, the sensitivity of hydrogen bubbling decreases with increasing pH, while when pH>6, hydrogen bubbling does not occur.
2) H2S concentration. The higher the hydrogen sulfide concentration, the greater the sensitivity to hydrogen bubbling.
3) Chloride ions. In the pH range of 3.5 to 4.5, the presence of Cl- increases the corrosion rate and increases the sensitivity to hydrogen bubbling.
4) Temperature. CLR is maximum at 25°C, and sensitivity to hydrogen bubbling is maximum. When the temperature is lower than 25°C, as the temperature increases, the corrosion reaction and hydrogen diffusion rate accelerate, thereby increasing the sensitivity to hydrogen bubbling. However, when the temperature is higher than 25°C, the sensitivity of hydrogen bubbling decreases due to the decrease in H2S concentration.
5) Time. The test uses 96h as a comparison. In general, as the test time increases, the degree of corrosion becomes more serious.