Mechanical Stress Effects on 550 °C Hot Corrosion Propagation Rates in Precipitation Hardened Ni-Base Superalloys: CMSX-4, CM247LC DS and IN6203DS

Combinations of temperature, stress and hot corrosion may cause environmentally-assisted cracking in precipitation-hardened Ni-base superalloys, which is little understood. This research aims to increase current understanding by investigating the effects of mechanical stress on the hot corrosion propagation rate during corrosion-fatigue testing of CMSX-4, CM247LC DS and IN6203DS. The parameters used during the tests included a high R-ratio, high frequency, and a temperature of 550 °C. The results showed CMSX-4 experienced a predictable increase in the hot corrosion rate, CM247LC DS also experienced increased rates, but no obvious trend was apparent; whilst IN6203DS showed no evidence of an increased rate. These different behaviours appear to be a result of an interaction between the mechanical stress and microstructural features, which include gamma-prime volume fractions in both the matrix and eutectic regions, along with the distribution of the eutectic structure. The different behaviours in the hot corrosion propagation rate subsequently affected the respective corrosion fatigue results, with both CMSX-4 and CM247LC DS experiencing fracture but with significantly more scatter involved in the CM247LC DS results. All IN6203DS corrosion-fatigue specimens completed the respective tests without fracture and showed no evidence of cracking. It, therefore, appears that precipitation hardened Ni-base superalloys, which are susceptible to environmentally-assisted cracking, also experience increased hot corrosion propagation rates.

Inspection and mitigation for pitting corrosion on stainless steel process piping to prevent process safety event and loss production opportunity in Medco E&P

Stainless steel piping has excellent corrosion resistant properties, both internal or external piping surface. In humid circumstances, sea vapor containing chlorine will be trapped on the pipe surface, especially pipes below deck with minimum sun exposure (more humid). Chlorine on the external pipe surface will damage the passive layer of stainless steel pipe. Damage speed is faster than recovery of passive layer stainless steel. This condition lead to a lot of localized pitting corrosion spread. The corrosion was detected visually and carried out with dye penetrant inspection to assure pitting condition. Actual dimension of pitting (depth, diameter) cannot be measured due to limitation of the NDE technique. This pitting corrosion can result hydrocarbon leakage as a process safety event that contributes loss of production opportunity. Without modification circumstances, this condition can be stopped immediately by application of a viscos elastic coating to prevent pitting corrosion propagation. Application of viscos elastic coating is simpler and faster when compared to conventional coating. Viscos elastic coating will protect stainless steel piping surface against oxygen and chloride in humid circumstances so that stainless steel can recover passive layer and stop pitting corrosion.

Numerical study on the flow characteristics of centrifugal compressor impeller with crack damage

The distribution and characteristics of internal flow field of the impeller with crack damage in service environment was investigated via numerical simulation with RNG k-ε turbulence model. The diffuser and volute are added based on the original impeller to simulate the internal flow field comprehensively. It was found that along the flow direction, the pressure, velocity, and temperature of the fluid increase continuously, and the maximum value appears near the outlet of the impeller. The maximum pressure and velocity in the crack area are distributed around the middle section and the trailing edge of the crack. Entropy production theory was applied in the study of internal flow, which reveals that the entropy production becomes larger around the crack. The further propagation of the crack is promoted by the opening force perpendicular to the entrance direction of the middle crack, the corrosion propagation at the rear edge of the crack, and the thermal deformation of the blade. The accelerated crack process will finally lead to the blade fracture accident.

The Corrosion Propagation Stage of Stainless-Steel Reinforced Concrete: A Review

Stainless steel (SS) reinforcement is increasingly used to control corrosion of reinforced concrete in aggressive marine and deicing salt service. It is well established that the chloride threshold of SS is greater than that of plain steel (PS) rebar, yielding substantially increased duration of the corrosion initiation stage. Much less known, however, is if there is a similar benefit to the duration of the corrosion propagation stage (tp). Thus, credit for increased tp in durability forecasts for SS use tends to be conservatively limited. To reduce that uncertainty the literature was gleaned for the few instances where SS reinforcement had reached, and preferably completed, the corrosion propagation stage. Particular attention was given to actual structural service experience, outdoor tests, and realistic laboratory conditions. Only a single case of actual service in a structure was found for which tp could be estimated, albeit indirectly. The result suggests a tp of several decades for the case of austenitic Cr-Ni rebar in marine service. Outdoor tests without unnatural acceleration showed a few cases where tp was reached, but only for straight Cr ferritic alloys which showed some limited improvement over tp for PS. With the additional insight from laboratory tests, it was concluded that SS rebar made with high pitting resistant grades, and thoroughly descaled, had a positive outlook for propagation stage durations that substantially exceed those of PS rebar. Quantification of that improvement is much in need of further field and laboratory assessment.