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Figure 2: Analyzed PSA vessels.

The PSA equipment

is a carbon steel

SA-516 gr. 70,

vessel whose

mechanical properties for the operational temperature

(40°C)

are: Young modulus

(207,000 MPa), Poisson ratio (0.3), Yield stress (262 MPa) and Ultimate tensile stress

(483 MPa), obtained from the ASME and data sheets.

Toughness is not obtained from tables. Instead, it is necessary to measure or

calculate. This work employs the Lower Bound Method, described by the API 579

.

56

036 .0 exp 084 .35.36 ;

110 min

ref

IC

TT

m MPa

K

(5)

In Eq. 5, T is the evaluation temperature,

40ºC,

and T

ref

is equal to

-6 °C,

obtained

from the Impact Test Exemption curve (ASME Section VIII Division 1 – UCS-66) for

the SA-516 gr. 70 and a thickness of

23.5 mm

(head thickness). Replacing all values in

Eq. 5, we obtain

m MPa m MPa

K

IC

158 ;

110 min

and then we select

m MPa

K

IC

110

, the maximum allowable toughness according to this methodology.

Material constants for using with Paris law was obtained from BS-7910 for steel in a

marine atmosphere. Point 1:

K=0, m=3.42, C=1.72x10

-13

; Point 2:

K=748

2

3

/

mmN

,

m=1.11, C=7.48x10

-7

.

Finite element model and fatigue results

Stresses were calculated using a linear elastic analysis on an axisymmetric Finite

Element model, implanted in the software Ansys Mechanical R. 11.0 SP1. Stresses were

used for both crack assessment and fatigue crack growth evaluation.

shows

both the geometric model and some mesh details from the interest regions.

745