API 579-2/ASME FFS-2 2009 Fitness-Fo Fitness-For-Service r-Service Example Problem Manual
PART 4 ASSESSMENT OF GENERAL METAL LOSS EXAMPLE PROBLEMS 4.1 4.2 4.3 4.4 4.1
Example Example Example Example
Problem Problem Problem Problem
1 2 3 4
......................................................................................................... 4-1 ......................................................................................................... 4-6 ....................................................................................................... 4-10 ....................................................................................................... 4-14
Example Problem 1
Internal corrosion on the cylindrical shell of a heat exchanger has been found during an inspection. Details regarding the heat exchanger and inspection data are given below. The heat exchanger was constructed to the ASME B&PV Code, Section VIII, VIII, Division 1, Edition 1989. Determine if the heat exchanger is suitable for continued operation. Vessel Data
Material
=
SA 516 Grade 60 Year 1989
Design Conditions
=
3.85
Inside Diameter
=
484 mm
Nominal Thickness
=
16 mm
Future Corrosion Allowance Future
=
2 mm
Weld Joint Efficiency
=
Tubesheet to tubesheet distance
=
1.0 1524 mm
Pa @ 380 C and full vacuum @ 380 C
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4-1
API 579-2/ASME FFS-2 2009 Fitness-For-Service Example Problem Manual
Inspection Data Based on a visual inspection, the corrosion loss is characterized as general, and point thickness readings will be used in the assessment (see paragraph 4.3.3.1 and 4.3.3.2). Point thickness readings were taken in accordance with paragraph 4.3.3.2. Table E4.1-1
Location
Thickness Reading
t , mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
13 12 11 13 10 12 11 12 13 13 11 12 12 13 13 -
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4-2
API 579-2/ASME FFS-2 2009 Fitness-For-Service Example Problem Manual
Perform a Level 1 assessment for internal pressure per paragraph - 4.4.2 a)
STEP 1 • Use the point thickness readings shown above; and determine the minimum measured thickness, t mm , the average measured thickness, t am , and the Coefficient of Variation, COV. A template for computing the COV is provided in Table 4.3 and is used in Table E4.1-2. Table E4.1-2
Location
Thickness Reading
trd ,i , i 1 to N
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
` ` , , ` , , , , ` , , , , ` , , ` ` , ` ` ` ` ` ` ` , , ` , , ` , ` , , ` -
13 12 11 13 10 12 11 12 13 13 11 12 12 13 13
t am
N
1
t N
rd , i
t rd ,i t am
(t rd ,i t am )2
0.9333 -0.0667 -1.0667 0.9333 -2.0667 -0.0667 -1.0667 -0.0667 0.9333 0.9333 -1.0667 -0.0667 -0.0667 0.9333 0.9333
0.8711 0.0044 1.1378 0.8711 4.2711 0.0044 1.1378 0.0044 0.8711 0.8711 1.1378 0.0044 0.0044 0.8711 0.8711
12.0667
S
i 1
1 S COV tam N 1 b)
N
(t
rd ,i
t am )2 12.9333
i 1
0.5
0.080
STEP 2 • The COV equals 8.0%, which is less than 10%; therefore, the average thickness to be used in the calculation is the average thickness of the thickness distribution, or
tam 12.0667 mm LOSS tnom tam 16 12.0667 3.9333 mm c)
STEP 3 ! Calculate the minimum required thickness (see Annex A). c tmin
t Lmin
PR
SE 0.6 P
PR
2SE 0.4 P
3.85(242 2 3.9333) 96.196(1.0) 0.6(3.85)
10.1670 mm
3.85(242 2 3.9333) 2(96.196)(1.0) 0.4(3.85)
4.9221 mm
c L max[10.1670,4.9221] 10.1670 mm tmin max tmin , t min
d)
STEP 4 • Determine if the component is acceptable for continued operation.
Perform a Level 1 assessment using Table 4.4.
(tam FCA 10.0667 mm) (tmin 10.1670 mm ) False Alternatively, the maximum allowable working pressure
AWP based on the average thickness ( t am ) can be
compared to the design pressure with the design pressure as the criterion.
4-3
API 579-2/ASME FFS-2 2009 Fitness-For-Service Example Problem Manual
t tam FCA 10.0667 mm AWP
SEt R FCA LOSS 0.6t
96.196110.0667 3.813 MPa (242 2 3.9333) 0.610.0667
3.813 MPa 3.85 MPa False The Level 1 assessment criteria are not satisfied.
Perform a Level 2 assessment for internal pressure using Table 4.4.
(tam FCA 10.0667 mm) ( RSFa tmin 0.9 10.1287 9.1158 mm) True Alternatively, the maximum allowable working pressure (
AWP ) based on the average thickness ( t am ) can
be compared to the design pressure with the design pressure as the criterion.
t
(tam FCA) 10.0667 RSF a
AWP
0.9
11.1852 mm
SEt R FCA LOSS 0.6t
96.196111.1852 4.225 MPa (242 2 3.9333) 0.6 11.1852
4.225 MPa 3.85 MPa True Check the minimum measured thickness criterion.
(tmm FCA 8 mm) max[0.5tmin 5.065, tlim ] tlim max[0.2t nom 0.216 3.200,2.500] 3.200 mm 8 mm (max[5.065, 3.200] 5.065 mm ) True The minimum measured thickness criterion is satisfied. The Level 2 assessment criteria for internal pressure are satisfied.
4-4
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