Sensitization stainless steels

Tubercles grow on nonstainless steels and some cast irons. Sensitized stainless steel and a few other alloys are rarely affected. Surfaces must... 

Figure 15.16 Schematic representation of sensitized stainless steel.

Critical factors. The critical factors governing weld decay include the use of a sensitized stainless steel and the exposure of this metal to an environment that is sufficiently aggressive to cause degradation in the sensitized region. 

Reheating and quenching sensitized stainless steel may not be practical in many cases. Note also that the quenching operation can induce substantial residual stresses and warpage. 

Ford, F. P., Modelling and life prediction of stress corrosion cracking in sensitized stainless steel in high temperature water , Proc. of ASME Fall Meeting, 1985... 

Fig. 40. The advantages of the DL-EPR are (1) only a 100 grit finish is necessary, as the anodic sweep cleans the surface, (2) intragrain pitting does not affect the ratio, and (3) no measurement of either surface area or grain size is necessary. The anodic sweep essentially gives an internal calibration for the method. Majidi and Streicher have shown excellent correlation between SL- and DL-EPR tests for Type 304 SS (32). DOS values measured by EPR have been included in models of intergranular SCC of sensitized stainless steel (34,35).

Figure 6.28 Schema of a grain boundary (on the left), and a concentration profile near the grain boundary (on the right) of a sensitized stainless steel type 304 6...

A schematic representation of downscan polarization curves using the EPR procedure is shown in Fig. 7.65 (Ref 93). A sensitized stainless steel will result in an anodic loop with size depending on the degree of sensitization. With the specified rapid downscan rate, the passive film... 

The Cr-depletion theory has been accepted as the mechanism by which a sensitized stainless steel becomes susceptible to intergranular corrosion [60]. Recall that a minimum of 10 to 13wt.% Gr in solid solution is required to form protective passive films on Fe-Ni-Gr alloys... 

Fig. 18 Cr-depletion profile across a grain boundary in a sensitized stainless steel. (Ref [61], from Corrosion of Stainless Steels A. John Sedriks, copyright John Wiley. Sons. Reprinted by permission of John Wiley Sons, Inc.)...

Fig. 9.22 SEM micrograph showing crack propagation modes (a) in as-received stainless steel and (b) in sensitized stainless steel [94]. 

AR334 1.44 Control of the use of sensitized stainless steel, ML003740109, May 1973. 

Microprobe scans of sensitized stainless steels have indicated chromium depletion and nickel enrichment at grain boimdaries [21]. Radioactive C introduced into an austenitic 18% Cr, 12.8% Ni, 0.12% C stainless steel has demon-... 

Extensive testing on stainless steel mockups, fabricated using production techniques, has been conducted to determine the effect of various welding procedures on the susceptibility of unstabilized 300 series stainless steels to sensitization-induced intergranular corrosion. Only those procedures and/or practices demonstrated not to produce a sensitized structure are used in the fabrication of RCPB components. The ASTM standard A 708 (Strauss Test) is the criterion used to determine susceptibility to intergranular corrosion. This test has shown excellent correlation with a form of localized corrosion peculiar to sensitized stainless steels. As such, ASTM A 708 is utilized as a go/no-go standard for acceptability. 

E. Regulatory Guide 1.44, Control of the Use of Sensitized Stainless Steel, is addressed in Section 5.2.3.4. 

RG. 4—Comparison of Intergranular corrosion in various acid solutions. Measurement of weight-loss and change in electrical resistance on sensitized stainless steel corroding in boiling 65 % nitric acid, and boiling sulfuric acid solutions containing cupric or ferric sulfate. Specimen 0.15 by 0.60 cm In cross section. 

EAC of Sensitized Stainless Steels in High Temperature Water... 

The film rupture/slip dissolution model has been proposed for many systems, including stainless steels in chloride solutions, Fe-Ni-Cr steels, low alloy steels, and mild steel in caustic environments, etc. But the see and eF of sensitized stainless steel in BWR nuclear plants is probably the most... 

Figure 5-49. Example of the application of a film rupture model to sensitized stainless steels in high temperature water (Ford, 1990) a) effect of crack tip strain rate, b) effect of corrosion potential.

Today, the general trend is to consider that transgranular crack propagation involves mechanical rupture and that the dissolution process may account for some intergranular cracking phenomena, particularly when the anodic behavior of grain boundaries is very different from the bulk material (for example, in sensitized stainless steels). 

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