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Hydrogen induced cracking (HIC) resistance of seamless pipel

Attention:     Issuing time:2019-12-12 10:10

Hydrogen induced cracking (HIC) resistance of seamless pipeline
 

Seamless pipeline is mainly used to transport high-pressure oil and gas near the wellhead. With the increasingly serious problem of hydrogen sulfide corrosion, the development of sulfur resistant seamless pipeline is imminent, and the performance of sulfur resistance is the key. The medium and material factors influencing the HIC properties are discussed. It is considered that the addition of Cu and Ni can improve the HIC properties of seamless pipeline materials, reduce the s content in steel, and reduce the sensitivity of hydrogen bubbling by spraying calcium silicate powder.
 
With the development of oil and natural gas exploitation, there are more and more oil and gas wells with complex exploitation conditions and sulfur-containing environment. In recent years, the demand for sulfur resistant seamless pipeline is increasing. Seamless pipeline is mainly used to transport high-pressure oil and gas near the wellhead. It is a seamless steel pipe without welding seam. This paper intends to discuss the research and manufacture of sulfur resistant seamless pipeline.
 

 
1 Test method
According to iso3183 standard, 7 heats of 1t ingot are smelted in the laboratory by immersion method. After forging, piercing, pipe jacking and stretch reducing, 20 mm × 100 mm × 5 mm plate thickness or tube thickness samples are cut off from the steel pipes, and immersed in the solution prepared according to the standard. After 96 hours, the sections are taken out and rolled vertically. Three parameters (crack length ratio CLR and crack thickness ratio CTR) are calculated by metallographic method In order to compare the sensitivity of HIC.
 

2 Factors affecting HIC performance
 
2.1 medium factor
1) pH value. A large number of research results show that in the range of pH 1-6, the sensitivity of hydrogen bubbling decreases with the increase of pH. when pH > 6, hydrogen bubbling does not occur.
2) H2S concentration. The higher the concentration of hydrogen sulfide, the greater the sensitivity of hydrogen bubbling.
3) chloride ion. In the range of pH 3.5-4.5, the presence of Cl - increased the corrosion rate and the sensitivity of hydrogen bubbling.
4) temperature. At 25 ℃, CLR was the highest and hydrogen bubble was the most sensitive. When the temperature is lower than 25 ℃, the corrosion reaction and hydrogen diffusion speed will be accelerated and the sensitivity of hydrogen bubble will be increased. However, when the temperature is higher than 25 ℃, the sensitivity of hydrogen bubbling decreases due to the decrease of H2S concentration.
5) time. 96 h was used as the contrast in the test. Generally, with the increase of test time, the corrosion degree tends to be serious.
 
2.2 material factors
2.2.1 effect of chemical composition
A round of steel grades designed according to different grades have been smelted in the laboratory. See Table 1 for specific composition, and HIC immersion test has been carried out for them. The bubble area of B2, B6 and B7 is obviously larger than that of B9 and B10. See Table 2 for the result of crack sensitivity index. It can be seen from table 2 that the HIC resistance of B2, B6 and B7 is significantly worse than that of B9 and B10. In Table 1, steel grades B2, B6 and B7 do not contain Cu and Ni, while steel grades B9 and B10 contain Cu and Ni. It can be seen that the addition of Cu and Ni makes the corrosion products form a protective film on the surface of the steel, inhibits the corrosion reaction on the surface, thus reducing the escape of hydrogen, reducing the hydrogen entering the steel matrix from the environment, reducing the hydrogen bubble sensitivity, and increasing the HIC resistance. This is in good agreement with the research results of oriani. Moreover, oriani also points out that only 0.2% Ni and a large Only 0.2% Cu can produce the effect.
 
Table 1 chemical composition
 
Chemical composition
Grade C Si Mn P S Cu Ni Nb V N Ti Mn
B2 0.084 0.27 0.67 0.015 0.0083 - - <0.01 <0.01 0.0022 - -
B6 0.150 0.29 0.95 0.015 0.0078 - - 0.027 0.065 0.0059 0.011 -
B7 0.140 0.44 0.88 0.014 0.0071 - - 0.027 0.065 0.0028 0.023 0.18
B9 0.082 0.17 0.84 0.014 0.0077 0.24 0.23 0.018 0.057 0.013 0.01 0.19
B10 0.13 0.30 0.83 0.014 0.0069 0.21 0.21 0.031 0.06 0.0019 0.019 0.20
 
 
Table 2 HIC test results
 
HIC test results
Sample number CLR CTR CSR
B2 2.79% 1.89% 0.13%
B6 12.31% 13.64% 2.81%
B7 26.47% 25.82% 6.14%
B9 0 0 0
B10 0 0 0
D2 0 0 0
C6 0 0 0
 
 
2.2.2 effect of sulfur content in steel
The chemical composition of B2 and D2 are almost the same, but the s content of D2 is far lower than that of B2. After immersion test (Table 3), it is found that the HIC resistance of D2 is much better than that of B2. It can be seen that increasing the purity of steel and reducing the sulfur content are beneficial to reducing the sensitivity of hydrogen bubbling. The main reason is that hydrogen atoms tend to accumulate at the tip of long MNS inclusions or alumina inclusions and form a great hydrogen pressure, resulting in internal bubbles in the material. Under the action of stress, hydrogen induced cracks pile up and arrange along the direction perpendicular to the stress axis, forming a chain like bubble, and finally a step like fracture. Therefore, reducing the sulfur content in steel can reduce the MNS formed, thus reducing the sensitivity of hydrogen bubbling.
 

2.2.3 effect of calcium treatment on HIC performance
B6 and C6 have the same composition, but B6 has not been treated by spraying calcium silicate powder, while C6 has been treated by ca. Immerse B6 and C6 in the artificial seawater solution specified in tm0284 for 96 h at the same time. It is found that the bubbling area of C6 surface is significantly reduced and there is no crack. See Table 4 for specific HIC test results. It can be seen from table 4 that the HIC resistance of Ca treated steel is significantly better than that of non CA treated steel. This is mainly due to the fact that the shape of sulfide and oxide inclusions is changed after the treatment of spraying calcium silicate powder, and the concentrated inclusions with edges and corners are transformed into dispersed particles inclusions, thus reducing the sensitivity of hydrogen bubbling and improving the HIC resistance.
 
Table 3 chemical composition of B2 and D2
 
Chemical composition of B2 and D2
Grade C Si Mn P S Cu Ni Nb V N
B2 0.084 0.27 0.67 0.015 0.0083 0.02 0.02 <0.01 <0.01 0.0022
D2 0.070 0.16 0.56 0.013 0.0025 0.02 0.02 <0.01 <0.01 0.0013
 
Table 4 chemical composition of B6 and C6
 
Chemical composition of B6 and C6
Grade C Si Mn P S Cu Ni Nb V N Ti Cu
B6 0.15 0.29 0.95 0.015 0.0078 0.02 0.02 0.027 0.065 0.0059 0.011 0.1500
C6 0.15 0.30 0.97 0.015 0.0050 0.02 0.02 0.033 0.075 - - 0.0039
 
 
3 Conclusion
1) the medium factors affecting HIC performance mainly include pH value, H2S concentration, chloride ion, temperature and time.
2) the addition of Cu and Ni can improve HIC resistance.
3) the sensitivity of hydrogen bubbling can be reduced by reducing s content and increasing purity of steel.
4) spraying calcium silicate powder is one of the most effective measures to reduce the sensitivity of hydrogen bubbling.
 
 

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