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RESEARCH PAPERS

# Effect of Rising and Falling $K$ Profiles on SCC Growth Rates in High-Temperature Water

[+] Author and Article Information
Peter L. Andresen, Martin M. Morra

GE Global Research, One Research Circle, CE 2513, Schenectady, NY 12309

J. Pressure Vessel Technol 129(3), 488-506 (Nov 28, 2006) (19 pages) doi:10.1115/1.2748830 History: Received December 07, 2005; Revised November 28, 2006

## Abstract

Effects of rising and falling stress intensity factor $(K)$ profiles on the stress corrosion cracking (SCC) growth rates of stainless steel and nickel alloys has been studied in high-temperature water. Sophisticated test control software was used that changes loading $(P)$ based on crack length $(a)$ to achieve a specific $K$ trajectory by controlling $dK∕da$, not simply $dP∕dt$. The majority of SCC problems develop adjacent to welds, which have a complex residual stress profile versus wall thickness. This, coupled with the dependence of $K$ on crack length, causes $K$ to change as the crack grows, not per se with time $(t)$. The effect of the rate of change in $K$ on crack tip strain rate and the associated crack growth rate is discussed, along with the repercussions to understanding and dispositioning SCC response.

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## Figures

Figure 18

SCC response in 288°C water containing 2000ppbO2 of specimen c247 of alloy 182 weld metal

Figure 19

SCC response in 288°C water containing 2000ppbO2 of specimen c247 of alloy 182 weld metal

Figure 20

SCC response in 288°C water containing 2000ppbO2 of specimen c247 of alloy 182 weld metal

Figure 21

SCC response in 288°C water containing 2000ppbO2 of specimen c290 of alloy 182 weld metal

Figure 22

SCC response in 288°C water containing 2000ppbO2 of specimen c290 of alloy 182 weld metal

Figure 11

SCC response for an unsensitized model “stainless steel” containing 5% Si with 22% CW at 140°C. The “varying-K” profile changed stress intensity factor (K) as the crack length (a) increased, using a dK∕da of −22MPa√mpermm(−500ksi√in.∕in.).

Figure 12

SCC response in 288°C water containing 1.58ppmH2(17.7cc∕kg) for unsensitized Type 304L stainless steel containing 1.5% Si with 21% reduction in thickness at 25°C

Figure 13

SCC response in 288°C water containing 1.58ppmH2(17.7cc∕kg) for unsensitized Type 304L stainless steel containing 1.5% Si with 21% reduction in thickness at 25°C

Figure 14

SCC response in 288°C water containing 1.58ppm(17.7cc∕kg)H2 (apart from the start of the test, as shown on the figure to the right) for unsensitized Type 304L stainless steel containing 1.5% Si with 21% reduction in thickness at 25°C

Figure 15

SCC response in 288°C water containing 2000ppbO2 of specimen c270 of wrought Alloy 182 containing 3% Si with 26% reduction in thickness at 25°C

Figure 16

SCC response in 288°C water containing 2000ppbO2 of specimen c160 of alloy 182 weld metal

Figure 17

SCC response in 288°C water containing 2000ppbO2 of specimen c247 of alloy 182 weld metal

Figure 1

SCC growth rate versus corrosion potential for stainless steels tested in 288°C high purity water containing 2000ppbO2 and 95–3000ppbH2

Figure 2

Stress intensity factor, K, versus crack depth for a 38mm(1.5in.) thick BWR core shroud. The calculated residual stresses (U shaped and positive at the inside and outside of the shroud, which is welded from both sides in alternating passes) were biased upwards by, 5ksi, 7ksi, and 10ksi (35MPa, 49MPa, and 70MPa) to account for fit up stresses that can occur in local regions of any weld. Because of stress relaxation from neutron irradiation, cracks that grow more slowly (e.g., at 0.1μS∕cm) don’t achieve as high a stress intensity factor.

Figure 3

Typical residual stress and stress intensity factor, K, versus crack depth for large diameter stainless steel piping. Upper and lower bound residual stresses were used to calculate different K profiles through wall. Local variations can occur because of fit up stresses and variations in the weld, but such variations cannot exist all around a given weld.

Figure 4

At static load, dynamic strain results from the redistribution of the stress and strain fields as the crack advances. This creates an interdependency in which the crack tip strain rate is responsible for crack advance, and crack advance then produces stress/strain field redistribution, i.e., crack tip strain rate (5,15-16,19,33-34).

Figure 5

SCC response in hydrogenated 288°C water for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at 140°C

Figure 6

SCC response in 288°C water with 2000ppbO2 for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at +140°C

Figure 7

SCC response under varying-K control in 288°C water containing 2000ppbO2 for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at +140°C

Figure 8

SCC response under varying-K control in 288°C water containing 2000ppbO2 for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at +140°C

Figure 9

SCC response under varying-K control in 288°C water containing 2000ppbO2 for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at +140°C

Figure 10

SCC response under varying-K control in 288°C water containing 2000ppbO2 for a 0.5TCT of unsensitized Type 316L SS with 20% reduction in thickness at +140°C

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