Example Problem 4
A dent containing a gouge has been found on a pipeline. The pipeline is
constructed to ASME B31.3.
Determine if the dent-gouge is acceptable for continued operation
using a Level 1 approach.
Pipeline Data:
• Material
• Dent Depth
• Gouge Depth
• Dent Radius
• Outside Diameter
• Measured Wall Thickness
• Allowable Stress
• Yield Strength
• Operating Pressure
• Minimum Temperature
• Future Corrosion Allowance
• Distance to discontinuity
• Distance to nearest weld
• Weld Joint Efficiency
= API L Grade X Year 5 42 1999
= 25.4 (mm measured during shutdown)
= 1.27 mm
= 50 mm
= 508 mm
= 12.7 mm
= 137.9 MPa
= 290 MPa
= 5.0 MPa
= 0° C
= 0.5 mm (internal)
= 1000 mm
= 300 mm
= 1.0 (machine welded)
Example Problem 4 – DENT-GOUGE ASSESSMENT
Inspection data:
 The dent is located on the base metal away from a weld and has a
smooth appearance. No cracking originating from the gouge has been
detected.
 Perform a Level 1 Dent-Gouge Combination assessment per API 579-1.
 STEP 1 - Determine the input parameters.
1) Calculate the maximum allowable working pressure.
Determine the future wall thickness:
tc = trd − FCA
tc = 12.7 − 0.5 = 12.2 mm
Calculate the maximum allowable working pressure:
Example Problem 4 – DENT-GOUGE ASSESSMENT
Determine whether the operating pressure is greater than or equal to
70% of the Max. Allowable Working Pressure (MAWP):
5.0 MPa ≥ ((0.7) (6.7533) = 4.7273 MPa)
True
The dent depth on the pipe in pressurized condition is therefore
calculated using equation the following equation:
ddp = 0.7dd0
ddp = 0.7(25.4) = 17.7800 mm
2) Gouge depth, dg = 1.27 mm
3) The minimum specified yield strength, σys = 290 MPa
4) Dent spacing to the nearest weld joint, Lw = 300 mm
5) Dent spacing to the nearest structural discontinuity, Lmsd = 1000
mm
 STEP 2 - Determine the future wall thickness. See STEP 1.
Example Problem 4 – DENT-GOUGE ASSESSMENT
 STEP 3 - Verify minimum required wall thickness.
tmm = trd - dg
tmm = 12.7 – 1.27 = 11.43 mm
tmm - FCA ≥ 2.5 mm
((11.43 – 0.5) = 10.93 mm) ≥ 2.5 mm
True
Verify minimum required distance to structural discontinuities:
Lmsd ≥ 1.8 √(Dtc)
1000 mm ≥ ((1.8) √(508)(12.2) = 141.7047 mm)
True
Verify minimum required distance to the weld:
Lw ≥ max. [2tc, 25 mm]
300 mm ≥ (max.[(2)(12.2), 25] = 25 mm)
True
Example Problem 4 – DENT-GOUGE ASSESSMENT
 STEP 4 – Determine the circumferential (hoop) stress:
 STEP 5 – Determine the parameters needed in Fig. 12.3 (API 579) –
the gouge depth to corroded wall thickness ratio:
The dent depth to component diameter ratio:
Example Problem 4 – DENT-GOUGE ASSESSMENT
The circumferential (hoop) stress to the Specified Min. Yield Strength
(SMYS) ratio:
Entering the data into Figure 12.4 it is shown that the intersection point is
above the relevant curve. The analyzed dent-gouge combination is
unacceptable
The Level 1 assessment criteria are not satisfied.
Design a repair.
Example Problem 4 – DENT-GOUGE ASSESSMENT
Figure 12.4: Interaction Diagram for Determining the Acceptability of a Dent-Gouge Combination (API 579-1)