Experimental Study on SCC Susceptibility of X60 Steel Using Full Pipe Sections in Near-Neutral pH Environment

Abstract

Stress corrosion cracking (SCC) tests were performed using the pipe section buried in a clay type of soil with the pH adjusted to near-neutral range. Pipe specimens with various sizes of fatigue pre-cracks ahead of artifical notch tips on the outer surface were subjected to cyclic loading tests. Maximum level of hoop stress was 105% SMYS, and R-value (Ratio of minimum load to maximum load) was 0.5. Growth of cracks was observed from the fatigue crack tips. Fractographic and metallographic examination has confirmed the quasi-cleavage nature of the transgranular SCC that is typically observed in near-neutral pH SCC. Crack depth measurement using DCPD method revealed the relatively high crack growth rate up to 10−5 mm/s. Metallographic examinations showed the existence of many micro-cracks associated with MnS inclusions in the highly strained field ahead of the initial crack tips. The relatively high crack growth rate may be caused by MnS inclusions. The loading rate, dJ/dt, was calculated for each crack condition in order to correlate qualitatively the crack growth rate with the loading rate. J-integral was calculated through non-linear FEM analyses for semi-elliptical cracks based on the stress-strain relationships obtained from the tensile tests using the same X60 steel specimen. Linear relationship was then obtained between the crack growth rate and the loading rate, and therefore the possibility to predict crack growth rates for various loading condition in the field was demonstrated.

Investigation of stress-corrosion cracking of welded joint of H70 steel under cathodic polarization in near neutral environment

“…2, a). The ferrite grain corresponds to the (10)(11) Microstructure of the external seam metal of welded joint is dispersed acicular ferrite with intergranular pre-eutectoid ferrite allocations in the form of thin continuous layers, individual grains, and individual coarse conglomerates of the socalled massive pre-eutectoid ferrite (Fig. 2, b, c).…”

Mechanical and Environmental Influences on Stress Corrosion Cracking of an X-70 Pipeline Steel in Dilute Near-Neutral pH Solutions

“…As a consequence, a lot of work about pipeline steels susceptibility to SCC in near-neutral pH solutions, including the infl uences of different parameters involved in promoting cracking, has been carried out in different laboratories throughout the world and many publications about this topic have appeared. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Such infl uences include loading conditions, temperature, pH, electrochemical potential, dissolved carbon dioxide (CO 2 ) content, metallurgy, and surface condition. This type of SCC is usually transgranular in nature, is sometimes called "TGSCC," and is associated with an appreciable amount of corrosion product within the crack enclaves, and a large quantity of iron carbonate is deposited near the failure sites.…”