PSI - Issue 14

S. Vishnuvardhan et al. / Procedia Structural Integrity 14 (2019) 482–490 S. Vishnuvardhan / Structural Integrity Procedia 00 (2018) 000–000

484

3

were carried out on Eccentrically-loaded Single Edge notch Tension [ESE(T)] specimens made of SA 333 Gr. 6 and SA 516 Gr. 70 steels under demineralized water and 3.5% NaCl aqueous environments. 2. Material Properties The steels used in the present study were SA 333 Gr. 6 carbon steel and SA 516 Gr. 70 carbon steel conforming to ASTM A 333 (2005) and ASTM A 516 (2010) respectively. SA 333 Gr. 6 steel is used in the fabrication of primary heat transfer pipe in nuclear power plant, operate at lower temperatures. Similarly, SA 516 Gr. 70 steel is used throughout oil, gas, petrochemical industry. This particular material is known for its weldability and improved notch toughness characteristics and is ideal for use in lower than ambient temperature services. Chemical analysis and tension tests were carried out on the samples. The chemical composition in weight for the SA 333 Gr. 6 steel was C = 0.124%, Mn = 0.919%, S = 0.001%, P = 0.003%, Si = 0.314% and the remainder was Fe and for SA 516 Gr. 70 steel was C = 0.168%, Mn = 1.08%, S = 0.001%, P = 0.004%, Si = 0.257%, Cr = 0.106%, Mo = 0.03% and the remainder was Fe. Mechanical properties of the samples were determined by carrying out tension tests by using a ±250 kN capacity Universal Testing Machine (UTM) as per ASTM E 8M (2011). Table 1 gives the mechanical properties of both the materials.

Table 1. Mechanical properties of SA 333 Gr. 6 and SA 516 Gr. 70 steels. Properties SA 333 Gr. 6 steel Column B ( t ) Experimental Specified as per ASTM A333/A333M - 05 (min.)

Experimental Specified as per ASTM A516/A516M - 10 (min.)

Yield strength, σ y (MPa)

310

240

330

260

Ultimate Tensile strength, σ u (MPa) Modulus of elasticity, E (GPa)

465

415

530

485-620

205

-

200

-

Elongation (%)

28.00

16.50

19.20

17

3. Specimen Details ASTM E 647-13 (2013) recommends mainly three types of specimens, viz., Compact [C(T)] specimen, Middle tension [M(T)] specimen, Eccentrically-loaded single edge notch tension [ESE(T)] specimen for carrying out FCG studies on materials. In the present studies, ESE(T) specimen was used. The main advantages of ESE(T) specimens are it gives additional working space and its design reduces the T-stress (stress parallel to the crack surface) and crack fracture paths are more self-similar than the other specimens. It is recommended that the thickness of the ESE(T) specimen be in the range of (W/20) ≤ B ≤ (W/4) Where W is the width of the specimen, B is the thickness of the specimen. The ESE(T) specimens made of SA 333 Gr. 6 steel were fabricated from a straight pipe having a length of 525 mm, outer diameter 415 mm and wall thickness 32 mm. The other ESE(T) specimens made of SA 516 Gr. 70 steel were fabricated from a plate of thickness 25 mm. The SA 333 Gr. 6 and SA 516 Gr. 70 steels were machined to get specimens of dimensions 277.5 mm x 75 mm x 8 mm. A straight machined notch of length 11.25 mm was made by electrical discharge machining process at the mid height of these specimens. 4. FCG Studies Fatigue crack growth (FCG) experiments were carried out under demineralized water and 3.5% NaCl aqueous environments by using a servo-hydraulic fatigue rated UTM of ±250 kN capacity. A corrosion chamber made of Perspex sheet was fixed to the test specimen at the notch portion; this chamber contained demineralized water / 3.5% NaCl aqueous solution to a depth of 45 mm. The corrosion process was accelerated by increasing the corrosion current,