PSI - Issue 3

J.L. González et al. / Procedia Structural Integrity 3 (2017) 48–56

51

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Author name / Structural Integrity Procedia 00 (2017) 000–000

2. Operating window estimation As mentioned before the plant operator had the need to operate the plant as long as possible in order to meet the refinery’s production demands, but at the same time, stop the operation just on time to avoid the collapse of the damaged section of the reactor. This extreme operating window may be estimated by the calculation of the creep rupture time by a proven engineering method as those depicted in Part 10 of the API 579/ASME FFS-1 [API (2007)]. The damaged section of the catalyzer reformer reactor is a cylindrical shell of 7200 mm (283.46”) external diameter, 25.4 mm (1”) thickness and vertical height of 3300 mm (129.92”). It is made of A 516 Gr 70 steel plate, butt welded to the rest of the reactor’s body. The design code is ASME Secc. VIII Division I, with maximum allowable operating pressure of .44 kg/cm2 (34.7 psi), design operation temperature of 722  C (1331.6  F) and maximum external shell temperature of 343  C (649.4  F). The collapse of the internal refractory lining caused temperatures in the shell above 450 ºC (842  F), with spots up to 600 ºC (1112  F); according to the paragraph 4.1.1 of the API 579/ASME FFS-1, the temperature limit to consider that A516 Gr70 steel plate is in the creep regime is 371 ºC, therefore the use of the methods depicted in Part 10 of the API 579/ASME FFS-1 standard is feasible, nonetheless since this is not a rigorous fitness for service assessment, some engineering criteria had to be used, as described below. 1. The failure mode is creep rupture under internal pressure and vertical dead weight load. Live and secondary loads are no considered in the assessment. 2. The effective stress in the deformed section of the shell is assumed to be the yield strength at the service temperature since the material has already plastically deformed. 3. The average service temperature assumed for the damaged ring is 538 ºC (1000  F). 4. The limit condition is creep rupture and the time of rupture is estimated following the procedure of a Level 2 assessment by Part 10 of API 579/ASME FFS-1standard. 5. The assessment is done in customary US units. The Table 1 summarizes the estimation of the rupture time following the procedure of a Level 2 assessment as for Part 10 of API 579/ASME FFS-1standard.

Table 1. Estimation of the creep rupture time of the damaged section of the reactor.

Step

Description

Data

Result

1

Assessment data:

Material

A 516 Gr70

Service Temperature

1000  F

Internal pressure

34.7 psig.

Internal Raduis

142”

Average measured thickness tam

1.000”

2

Effective stress from Table F.2

22.2 psi

Yield strength at 1000  F

3

Larson-Mille parameter at Seff) from Table F.31

LMP(Seff) =45.56157 – 3.9292158 ln(Seff)

33.38

  eff

730 h 14 min

4

Creep rupture time (L)

1000

LMP S

logL

C





LMP





460

T



C LMP = 20.0

The estimation of the creep rupture time is 730:14 h, which roughly corresponds to 30.4 days. Now it is clear that