Susceptibility of steel pipes to cracking in subsequently contact with solutions –either wet sour gas or near neutral solutions- is a dominant factor for residual life of gas-linepipes. Three different cracking phenomens are cause of a major concern for applications in wet H2S environments, namely Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC) and Stress Orientated Hydrogen Induced Cracking (SOHIC). Whereas laboratory test methods for HIC without mechanical loading are established for pipeline steels the situation is different in cases with external stress or additional strain. If the coating is damaged and a near neutral liquid medium is penetrating to the pipe surface a strain induced crack might occur. This type of corrosion is named Near Neutral SCC (NNSCC). A qualified test method for steels - specimens of hot strip, heavy plates and pipes- with simulated cyclic loading conditions for linepipes was not available. A multivalent test stand including pulsating tension on a high level qualified for high strength steels, wet environments with pH-values between 2.7 (sour gas) and 8.3 (synthetic seawater) and bubbling several gases with partial pressures of 0.005 to 1 kPa such as H2S, CO2 or N2 through a test solution with controlled temperature 15°C to 30°C (+/-0.2°C) was developed. This special test equipment is based on a Constant Elongation Rate Tension (CERT)-machine combined with a container for the fluid drive and a data collector. Different loading conditions (saw tooth, sinus, stepwise, constant and complex) in the range of 0 to 100% -i.e. 70% to 90%- of the parent material yield strength were carried out.
Keywords: sour gas, HIC-Test, SOHIC, NNSCC