From the surface roughness measured, it is clear that continuous flow of water is achieved only at SOD of 50mm. At 75mm SOD, the water flow loses it energy and falls in divergent manner. As there is no continuous flow of water at this distance, surface roughness values are high compared to other conditions. When the effect of pressure is considered in surface roughness in this process, it has not much significant effect in varying surface roughness. Thus it is understood that continuous flow of water alone determines surface roughness. Moving towards the nozzle of the water jet, finer surface texture might be achieved and moving still closer beyond a particular distance will result in material removal instead of peening which is not preferred.
Corrosion rate is measured using weight loss method. The samples are immersed in the corrosive environment of concentrated hydrochloric acid (35%) for a time period of 48 hours. Concentrated HCl was chosen as corrosion environment (chlorine environment – the most influencing cause for SCC) as it is most effective corrosive medium. It undergoes following chemical reaction, forming a corrosion product – FeCl2
2Fe + 4Hcl 2FeCl2 + 2H2
Weight loss in milligrams is measured for every 24 hours and corrosion rate in miles per year are calculated and tabulated and shown in table 3.
It is observed that the corrosion rate of the sample peened under the condition 300MPa-50mm, 75mm shows better stress corrosion resistance when compared to other peened parameter and the as welded sample. The samples peened with 250MPa-50mm also has high resistance towards stress corrosion which indicates that inducing high compressive stresses will results in increased resistance towards stress corrosion. Considering the results of surface roughness in SCC, samples peened at minimum SOD (50mm) has lower surface roughness which leads to increased resistance of stress corrosion. Rougher surface will act as a site for corrosion. Thereby optimising the parameter that will create low surface roughness with high compressive stress helps to achieve much better resistance toward SCC.
The samples peened with SOD of 50mm shows reduced stress corrosion rate when compared to 75mm SOD samples. This effect is observed due to the presence of high compressive residual stresses induced by high pressure water droplets with SOD of 50mm. Samples peened with high water pressure and smaller SOD shows increased resistance towards stress corrosion.
An exploratory research on water jet peening of TIG welded 316L SS plates was conducted using 6 different conditions by varying pressure (200,250 & 300MPa) and SOD (50 & 75mm). It was observed that high pressure water jet creates local plastic deformation, thereby inducing residual compressive stress on the weld surface. WJP with 50mm SOD shows better properties compared to 75mm.
• Columnar grains of TIG welded samples becomes finer grains after water jet peening on the surface level
• High hardness of 237 HV was obtained on 250MPa-50mm condition but effect of peening is limited to surface level whereas 300MPa (50 & 75mm) condition results in high depth of penetration of hardness from surface to subsurface level.
• High residual compressive stress of 118.8MPa is induced on the surface when peened under 250MPa50mm condition.
• Surface roughness depends mainly on SOD & not much on pressure was recorded. WJP with 50mm SOD shows lower roughness which was the result of continuous flow of water.
• Stress corrosion resistance increases for 50mm compared to 75mm and high resistance towards stress corrosion was observed on 300MPa (50 & 75mm) and also on 250MPa-50mm condition as a result of high residual compressive stress induced by high pressure water jet.