PSI - Issue 5

Rui F. Martins et al. / Procedia Structural Integrity 5 (2017) 640–646 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

642

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2. Materials and Methods

2.1. Materials

Three different materials, namely an AISI 316L austenitic stainless steel, a 445M2 ferritic marine stainless steel and a Chromium-Manganese austenitic stainless steel, were considered in the numerical analyses, in order to assess the differences that the type of material could cause in the mechanical and thermal behaviour of the exhaust systems. The mechanical properties for some working temperatures of each stainless steel were obtained from Martins (2005), Cruz et al. (2010), Martins et al. (2010), Australwright, and are presented in Table 1. The chemical compositions of the stainless steels referred in Table 1 are presented in Table 2, and each determines the mechanical behaviour and the corrosion resistance of each material, as shown in (Cruz et al. 2010).

Table 1. Mechanical properties of the stainless steels considered in the structural assessments.

Yield strength at 24º C (MPa)

Tensile strength at 24º C (MPa)

Yield strength at 350º C (MPa)

Tensile strength at 350º C (MPa)

Yield strength at 500º C (MPa)

Tensile strength at 500º C (MPa)

Material

AISI 316L austenitic stainless steel Chromium-Manganese austenitic stainless steel 445M2 ferritic marine stainless steel

290

560

233

484

210

410

430

800

270

510

260

500

350

520

---

---

---

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Table 2. Chemical composition of the structural stainless steels considered in the assessments.

Material

Chemical composition

C

Si

Mn

P

S

Cr

Mo

Ni

Cu

V

N

AISI 316L austenitic stainless steel

0.05 0.37 1.30 0.03 0.004 17.34 2.23 11.11 0.22 0.07

0.08

C

Si

Mn

P

S

Cr

Mo

Ni

Cu

V

N

Cr-Mn austenitic stainless steel

0.05 0.34 6.54 0.02 0.001 18.31 0.10 4.40

0.16 0.06

0.18

C

Si

Mn

P

S

Cr

Mo

Ni

Nb

Ti+Al

N

445M2 ferritic marine stainless steel

0.01 0.18 0.20 ----

----

22.1

1.20 ----

0.23 0.19+0.09 ----

Additionally, these exhaust systems work in a highly corrosive environment. Hence, the pitting corrosion resistance was evaluated taking into account the percentages of Chromium, Molybdenum and Nitrogen (Eq. 1) (Kovach 2000), and the pitting resistance equivalent number for each material (PREN) was calculated (Table 3).

PREN = %Cr+3.3× %Mo+16× %N

(1)

Table 3. Pitting resistance equivalent number (PREN) of the stainless steels considered in the structural assessments. Material PREN AISI 316L austenitic stainless steel 17.34+3.3×2.23+16×0.08= 25.98 Cr-Mn austenitic stainless steel 18.31+3.3×0.10+16×0.18= 21.52 445M2 ferritic marine stainless steel 22.1+3.3×1.20+16×0= 26.06

In addition, since the exhaust systems can reach temperatures up to 500 ºC, specific thermal properties of the materials, such as thermal conductivity and thermal expansion coefficient, were very important to define in order to estimate deformations and temperature distributions in the exhaust systems. Table 4 shows some physical values for some relevant temperatures ( Matweb and Australwright ).