Fatigue Strength In Air Research Articles

The Effect of Cathodic Protection on the Corrosion Fatigue Behavior of Carbon Steel In Synthetic Sea Water

Certain questions can be asked about the steel used on offshore platforms: What effect do the various properties of the steel have platforms: What effect do the various properties of the steel have on its corrosion fatigue behavior in sea water? What effect does cathodic protection have on this behavior? Is there a combination of properties, cathodic protection, and coatings that will yield optimum properties, cathodic protection, and coatings that will yield optimum fatigue performance? Here are some answers. Introduction Metallurgical study of structural failures in four offshore platforms has shown that the primary mode of failure was brittle fracture and that failure occurred almost exclusively near weld areas. Although some laminations in the steel and some weld failures were found, it has been reported that the primary cause of failure was the extremely high notch brittleness of the steel used in these structures. To prevent recurrence of this type of failure, changes in steel chemistry and microstructure have been recommended that greatly improve the mechanical and metallurgical properties of the steel. It has been further properties of the steel. It has been further recommended that a notch toughness specification be included in the over-all steel specifications. The recommended changes should significantly reduce the occurrence of failures of this type in future platforms. Once brittle failures are eliminated or reduced to an acceptable minimum, it is necessary to consider the problem of fatigue failures. The combination of a corrosive medium (aerated sea water) and cyclic loading due to the wind and wave action makes this type of failure a very real possibility. The critical area will be the welded tubular joints. To evaluate the possible contribution of this failure mode, several questions need to be answered: What effect do the various compositional, microstructural, and mechanical properties of the steel have on its corrosion fatigue behavior in sea water? What effect does cathodic protection have on the corrosion fatigue behavior? Is there a combination of properties, cathodic protection, and coatings for optimum fatigue performance? protection, and coatings for optimum fatigue performance? Corrosion Fatigue Behavior of Carbon Steel It has been conclusively shown that most metal treatments that are of great benefit in extending air fatigue life are usually of very limited help in a comoske environment. This is graphically illustrated in Fig. 1 for fresh water. The results show that the fatigue strength in air (endurance limit at 10(7) cycles) is approximately proportional to tensile strength. The fatigue strength of the carbon and low-alloy steels in water, however, is almost independent of the tensile strength. All the results on carbon steels, covering a range of carbon content from 0.03 to 1.09 percent, both annealed and hardened and tempered, showed corrosion fatigue strengths between 12,000 and 22,000 psi. For the low-alloy steels, with tensile strengths ranging from 80,000 to 224,000 psi, the range was 11,000 to 27,000 psi. JPT P. 283

FATIGUE STRENGTH OF PRESTRESSED CONCRETE FLEXURAL MEMBERS.

Keywords IMPERIAL COLLEGE FATIGUE, CONCRETE, INVESTIGATIONS, BONDED, POST TENSIONED, EFFECT, BONDS, STRESS, PATTERNS, STRANDS, THEORY, PREDICTION, INSTRUMENTATION, FATIGUE LIFE, STRENGTH, FLEXURAL, CRACKING, BEAMS, STATIC, LOADS, FACTORS, DEFORMATION, AIR, REDUCTION, FRACTURE, FLEXURE, EQUIPMENT, ESTIMATING, PRESTRESSED, MEMBERS, FAILURES, I BEAMS, TESTS, REPEATED, STEEL, CRACKS, PRESTRESSING, EMBEDDED, REINFORCEMENT, RANGE, BEHAVIOUR, LIFE... Show All

Estimation of Corrosion Fatigue Strength by Corrosion Resistance and Notch Sensitivity of Materials

Corrosion fatigue tests of various materials have been carried out in 1% saline and in 0.3N hydrochloric acid, accompanied with the measurements of corrosion current and notch sensitivity. In corrosion fatigue the critical depth of pits from which fatigue cracks initiate is determined by the stress concentration of pits depending on the corrosion resistance of materials and by the notch sensitivity. Corrosion effects κ (the ratio of fatigue strength in air σ to that in corrosive media σc) are referred to the static and the dynamic corrosion resistance, which are indicated by the corrosion current density ic0 at the beginning of the tests and by the inclination s of the corrosion current-testing time curve respectively, and to the notch sensitivity which is obtained by fatigue tests in air with notched specimens. Finally Eq. (14), (κ-1)/η=K3K4√((e<SUP)<K1K2>-1)/K1>√(i<SUB)c0τT> is obtained. (κ-1)/η is proportional to K3K4√(i<SUB)c0τT> for the same corrosive media irrespective of materials and of testing conditions. Test results show a linear relation between (κ-1)/η and √(i<SUB)c0τT> for the variety of materials, K3 and K4 being constant for the materials used in the present experiment. Thus, the meaning of the corrosion effect κ proposed by one of the authors is made clear. Besides sτT=K1 is obtained between the corrosion fatigue life τT and the dynamic corrosion resistance s, where the value of K1 is 4 in 1% saline and 2 in 0.3N hydrochroric acid.

Repairing defects of the open crack type by a diffusion metallization method

It was demonstrated that it is possible to “heal” defects of the open crack type of various origins in structural steels by the formation of diffused copper and chromium coatings. This method makes it possible fully or partially to restore to steel its compactness and strength, especially its fatigue strength in air and in corrosive media.

腐食疲労強度に及ぼす腐食液温度の影響

Corrosion fatigue tests were carried out in the solution of NaCl at -5, 20, and 70°C. The corrosion effect k, which is the ratio of the fatigue strength in air to the one under corrosion at the same cycles, is indicated by k=1+Ae-B/T, by using the absolute temperature T of the corrosive solution. Further, the corrosion fatigue strength σC is given by σC=σB×A'eB'E, where σB is the ultimate tensile strength and E is the potential vs. saturated calomel cell. It may be concluded that the corrosion fatigue strength is decided by the intensity of corrosion and the strength of materials and also by the notch sensitivity of corrosion cracks.