Prestressed hydrogen embrittlement

A prestressed roller bearing is used to detect the presence of hydrogen sulfide, but more specifically it is used to test for hydrogen embrittlement tendency of the drilling fluid. When introduced to the environment, the bearing has sufficient residual stresses to cause failure if sufficient hydrogen sulfide concentration is present. 

On high-strength steel used in prestressed concrete (but not with common reinforcing steel) under very specific environmental, mechanical loading, metallurgical and electrochemical conditions, hydrogen embrittlement can occur, which may lead to brittle fracture of the material (Chapter 10). 

Consequences of pitting corrosion may be very serious in high-strength prestressing steel, where hydrogen embrittlement can be promoted this is discussed in Chapter 10. 

Figure 10.6 Fracture surface of a prestressing bar that failed due to hydrogen embrittlement...

As far as corrosion behaviour is concerned, prestressing steel needs to be distinguished from reinforcing steel with regard to hydrogen embrittlement, since it only affects the former this has been illustrated in Chapter 10. 

Trials. The effectiveness of chloride extraction depends on characteristics of individual structures, such as the concrete composition, the actual chloride-penetration profile and the depth of cover. So, it may be useful to carry out a trial on an area (about 1 to 10 m ), which must be representative of the structure to be treated and should last at least 4 to 8 weeks. The results of such a trial in terms of the chloride profile before, during and after chloride extraction gives an indication of the duration required and can be used to show that chloride-extraction treatment of the particular structure will be effective under field conditions. Trials are most certainly recommended if prestressed structures are to be treated with chloride extraction. Careful monitoring of the potential of the prestressing steel should be carried out to establish the risk of hydrogen embrittlement. As a safe criterion, the potential should not become more negative than -900 mV SCE, as apphes for cathodic protection [13]. 

Prestressed concrete pipelines occasionally require cathodic protection. Protection must be done carefully to avoid damage to the prestressing wire from hydrogen embrittlement or SCC [75]. 

The problems of hydrogen embrittlement and of gas evolution are usually controlled by limiting the potential of the steel to below the hydrogen evolution potential. However, in acidic pits or crevices it may be possible for the potential to exceed the hydrogen evolution potential without being sensed by measuring electrodes. The cathodic protection of prestressed structures should only be undertaken with great care and input from experienced corrosion experts. An excellent state-of-the-art report on the cathodic protection of prestressed has been published (NACE, 2001). 

The steel should not exceed the hydrogen evolution potential, especially for prestressed steel to avoid hydrogen embrittlement. 

Prestressing Ok Ok Ok Difficult Ok Very difficult ICCP cathodic reactions risk hydrogen embrittlement... 

The problem of hydrogen embrittlement and prestressing steel has been discussed in Section 7.8 for cathodic protection, and Section 7.11.5 for realkalization. The realkalization process applies 20-50 V DC between the anode and the steel. It must therefore send the steel potential well beyond the level needed for hydrogen evolution. 

Is there a risk of hydrogen embrittlement of prestressing steel ... 

Chloride removal cannot be applied to prestressed structures due to the risk of hydrogen embrittlement. The use of lithium-based electrolytes suggests that ASR can be controlled. As stated earlier for impressed current cathodic protection, there must be electrical continuity within the reinforcement network for any of the electrochemical techniques to be applied. We do not know how long the treatment process will last but a range of 5-20 years is likely, depending upon conditions. 

Most standards state that cathodic protection should not be applied to prestressed concrete structures. This is because of the risk that if the potential exceeds the hydrogen evolution potential, hydrogen embrittlement could occur with potentially catastrophic failure of the steel These problem, were discussed in Sections 6.2.1 and 6,5. High strength steel may trap atomic hydrogen which weakens grain boundaries and the crystalline structure. There are several issues that can be considered when considering cathodic protection of prestre,ssed concrete structures ... 

Continuity and short circuits can be remedied prior to installation if necessary. At present all applications of cathodic protection to structures with prestressing are experimental with the exception of the cathodic prevention applied to new bridges in Italy to keep corrosion from initiating. This uses very low level currents and voltages with. special control system. to prevent hydrogen embrittlement,... 

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