Hydrogen Pipeline GH

The expected frequency of the GH2 pipeline is estimated from the base failure rate for the pipelines given in Table 4-5. It allows one to focus on the likelihood of holes and ruptures. These rates now need to be adjusted to the increased wall thickness used for this pipeline as compared to the typical wall thickness for this diameter. Table 5-22 shows reduction factors of the failure rates for pipe rupture and holes recommended by [3]. The factors were judged based on the benefits of increased wall thickness and surveillance. The likelihood of a rupture or hole was judged to decrease by a factor of roughly 0.7 overall. Looking at individual causes, external interference and material failure/construction defects were also found to decrease by a factor of roughly 0.7. The likelihood of a corrosion-induced failure doubled while other causes were considered only half as likely. Given that a special surveillance system is to be put into place, whereby the pipeline right-of-way will be visually checked once a day, the likelihood of an external interference event is expected to be reduced. Since it is possible that a repair or construction crew could get set up between line surveys, and because some external interference events are due to natural causes that are not affected by the line surveillance, only a 50 percent credit is given. For example, rupture and hole by external interference (in Table 4-5) have been corrected as: ruptures is equal to 3.3 x 10-5 /km-year (i.e. 9.8 x 10-5 /km-year x 0.35); and holes is equal to 7.4 x 10-5 /km-year (i.e. 2.1 x 10-4 /km-year x 0.35). With the same procedure, the result is shown in Table 5-23.

Table 5-22 Reduction factors for failure rates for rupture and hole [3]

Causes of the Pipe failure Wall Thickness Surveillance

Total reduction factor

External interference

0.7 0.5

0.35

Corrosion

1.0 1.0

1.0

Material failure/construction defect

0.7 1.0

0.7

Other

1.0 0.5

0.5

Table 5-23

Estimated failure rates of GH2 pipeline for rupture and hole [/km-yr]

Size

External Interference

Corrosion

Material failure/ construction defects

Others Total

Rupture

3.4E-05

1.3E-06

9.2E-06

2.0E-06 4.7E-05

Hole

7.4E-05

1.4E-06

2.2E-05

1.2E-04 2.2E-04

Total

1.1E-04

2.7E-06

3.1E-05

1.3E-04 2.7E-04

Table 5-24 Expected release frequency of the GH2 pipeline [/yr|

Release size

External Interference

Corrosion

Material fail/ const. defects

Others

Total

Percentage

Pipe rupture

3.6E-05

1.3E-06

9.6E-06

2.1E-06

4.9E-05

32.9%

Hole in the pipe

7.7E-05

1.4E-06

2.3E-05

6.5E-07

1.0E-04

67.1%

Total

1.1E-04

2.7E-06

3.3E-05

2.8E-06

1.5E-04

100.0%

Table 5-25 Accident outcome frequencies of the GH2 pipeline

Release Size

Incident Outcomes

Conditional Probabilities on Release

Outcome Frequencies (/yr)

Pipe rupture

Jet Fire

0.164

2.5E-05

Late Explosion

0.015

2.2E-06

Flash Fire

0.059

8.8E-06

Hole in the pipe

Jet Fire

0.336

5.0E-05

Late Explosion

0.030

4.5E-06

Flash Fire

0.121

1.8E-05

No effect

0.275

4.1E-05

Overall

1.000

1.5E-04

The general calculation procedure for pipelines involves multiplying a pipeline failure rate per km-year (Table 5-23) by the pipeline length and by a release probability, which might be the chance of a significant release. Thus, the overall frequency of a release is calculated using Eq. 4-8. Assumed that the conditional probability for release is 0.02, the release frequency of the GH2 pipeline with a length of 53 km is given in Table 5-24. This table shows that the total failure rate of the pipeline is 1.5 x 104 /yr (once per 6,666 years). This table also shows that the probability of the pipe rupture (32.9%) is less than that for leak in the pipe (67.1%).

The accident outcome frequencies were calculated by multiplying the expected initiating frequency (Table 5-24) with the outcome probabilities resulting from the event tree diagram (Fig. 4.6) for the continuous release. Table 5-25 shows that the fire mostly dominates the accident outcomes (accounting for 68%). Only 4.5% of the accident outcome may lead to an explosion and the remaining (27.5%) of the accidents have no effect on the population.

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Responses

  • Beatrice
    How do derive reduction factor in external interference total failure?
    7 years ago

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