Case study planning for an industrial water pipeline

Background, scope and objectives

A mine site in the mountains required additional water. This was to be generated by desalination of seawater near the coast; it would then be pumped to the mine. The water was suitable for industrial purposes, but not for domestic consumption nor agricultural use.

Table 10.4—Benefits of selecting Tender A (summary)

Benefit

Implications

Duration of work shorter by 10 days

Faster mobilization

More experienced personnel

Long history with the client

Dry dock instead of crane

With the stand-by buoy and its restricted flow rates, loading is expected to take about 29 hours. Demurrage is payable if loading extends beyond 30 hours. Delays are unlikely with careful management of loading operations. Nevertheless, if there were a delay it would be costly for the owner. The extended use of the stand-by buoy increases this risk.

This provides more flexibility and allows better planning, with less risk to the loading schedule.

More experienced personnel will do a better job. This is particularly important when refurbishing some of the control equipment in the SPM, which requires careful handling.

More experienced personnel are likely to generate fewer contract variations, and the speed (and price) of rectification of latent defects is likely to be better.

This is likely to provide better project and commercial outcomes, due to the good working relationships between the companies.

Tenderer A will use a dry dock for the overhaul, while Tenderer B will use a crane. The dry dock will impose less structural stress on the buoy, providing better life extension.

The landform and the presence of a nearby village restricted the possible pipeline route. The 28-inch (711 mm) pipeline had to cross the back of a hill behind the village. Along this section the water was at a very high pressure, with a high static head and large inventory due to the length of the pipeline run to the end of the first section.

A major failure of the pipeline above the village could result in a disaster, with water and mud running through the village, potentially killing people and destroying homes. Pipeline failure could arise from natural causes such as earthquake, from accidental damage by an excavator or other digging equipment, or from intentional tapping into the line to gain access to the water.

The risk assessment considered only the section of pipeline that ran past the village. The objectives of the assessment were to:

• understand the risk of pipeline damage, its likely causes and consequences;

• develop risk treatment actions appropriate to the level of risk.

The assessment was conducted by four people over a period of three hours.

Risk assessment approach

Prior to starting the assessment, it had been suggested that a detailed quantitative risk analysis would be needed. This would have been time-consuming and costly, and it was noted that quantitative estimates of the likelihood of pipeline failure could be only guesses. It was concluded that a quantitative assessment would be difficult and based on data that could not be suitably supported, and so a simpler approach was adopted.

The assessment team examined the risk of pipeline failure and developed plausible failure scenarios. The consequences and likelihood of each scenario were analysed to provide qualitative estimates of the levels of risk. Based on these estimates, treatment actions were developed and evaluated. The risks were reassessed with the proposed treatments in place and confirmed as tolerable.

Context and risk analysis scales

After considering the stakeholders and their needs, a set of criteria was developed (Table 10.5).

The analysis of scenario risk used a process similar to that discussed in Chapter 4. The consequence scale (Table 10.6) was linked to the criteria, and a simple likelihood rating was adopted (Table 10.7). The matrix shown in Figure 10.3 was used to derive risk priorities.

Table 10.5—Criteria

Criterion Notes

Safety and environment Safe and environmentally acceptable implementation and safe and environmentally acceptable resultant facility Public image and reputation Government, shareholder and community support

Performance Performance, reliability and availability as required

Costs and timing Capital, operating and maintenance costs within budget

Implementation to schedule

Table 10.6—Consequence scale for the water pipeline

Rating Potential impact on the criteria

Table 10.6—Consequence scale for the water pipeline

Rating Potential impact on the criteria

A

Catastrophic

Most criteria may not be achieved, several severely affected, includes multiple

fatalities

B

Major

Most criteria threatened, one severely affected, includes a single fatality

C

Moderate

Some criteria affected, considerable effort to rectify, includes severe injury

D

Minor

Remedied, with some effort the criteria can be achieved, includes injuries

requiring treatment

E

Insignificant

Very small impact, rectified by normal processes, includes very minor injuries

Table 10.7—Likelihood rating for the water pipeline

Rating

Interpretation

A

Almost certain

Very high probability of occurrence, could occur several times during a year

B

Likely

High probability, may arise once in a one to two year period

C

Possible

Possible, reasonable probability that it may arise during a five to ten year period

D

Unlikely

Plausible, but could occur during the next ten to twenty years

E

Rare

Very low likelihood, but not impossible, unlikely during the next ten years

Consequences

Likelihood

Severe A

Major B

Moderate C

Minor D

Insignificant E

A Almost certain

Extreme

Extreme

High

Medium

Medium

B Likely

Extreme

High

Medium

Medium

Medium

C Possible

High

High

Medium

Medium

Low

D Unlikely

High

Medium

Medium

Low

Negligible

E Rare

Medium

Medium

Medium

Low

Negligible

Figure 10.3—Priority matrix for the water pipeline

Figure 10.3—Priority matrix for the water pipeline

Scenarios and risk assessment

Four scenarios were developed (Table 10.8). They were discussed individually and relevant factors influencing the consequences or likelihood of the associated risk were noted (Table 10.9).

The consequences and likelihoods of the scenarios were analysed and combined to derive the levels of risk shown in Table 10.10.

Table 10.8—Pipeline failure scenarios

Scenario

Description

1. Natural disaster

2. Accidental digging into the pipeline

3. Purposeful attempt to tap into the pipeline to obtain water

4. Pipeline failure due to poor installation and testing

A landslip or earthquake that breaks the pipeline across its full diameter. The water would generate a mudslide that impacts on the village, kills many people, destroys many homes and receives national and possibly international press coverage.

A large leak due to mechanical impact. The water would generate a mudslide that impacts on the village, kills many people, destroys many homes and receives national and possibly international press coverage.

The effect would be a hole in the pipeline (estimated as a 25—50 mm hole near the top of the pipe) and the likely death of the person tapping into the pipe. The leak would have to continue for an hour or more to cause any flooding damage, but it would be very obvious (a fountain). There would be no other fatalities.

A failure when the pipeline is fully pressurized with water, with a break in the worst case up to the full diameter of the pipe. This would cause a flood and mudslide into the village with the potential for multiple fatalities.

Table 10.9—Contributing factors to pipeline failure

Scenario

Contributing factors

1. Natural disaster

2. Accidental damage

3. Wilful damage

4. Poor installation

Earthquakes have occurred in the region, but none have involved faulting and shear forces capable of breaking a pipeline.

A major earthquake of this magnitude would cause a great deal of damage of which the pipeline rupture would be a relatively minor part. The frequency of this was estimated as less than once per 1,000 years, a very rare event.

The only excavators in the village belong to contractors, most of whom have a working relationship with the company and are therefore highly likely to know of the line.

There will be a maintenance access road beside the line. It will be used for regular inspections.

There will be signage along the route indicating the pipeline location.

The villagers do and will know of the existence of the line.

The local authority has a strict permitting system for the kind of work that might dig into the line. The process would involve consideration of the pipeline.

A second pipeline maybe installed in the future, and this would most likely run in the same easement. It is conceivable that the installation contractor for the new line could accidentally dig into the operating water line.

It is most unlikely that an attempt would be made to tap the pipeline in the open above the village. It is more likely to occur in a concealed location, such as in the valley and therefore with a lower risk of a significant impact on the village.

Poor pipeline installation and testing procedures without precautions would contribute to this.

Table 10.10—Pipeline scenario risk assessment

Scenario Consequences Likelihood Level of risk

1. Natural disaster Catastrophic (multiple fatalities and Rare Medium large scale damage)

2. Accidental damage Catastrophic (multiple fatalities and Unlikely High large scale damage)

3. Wilful damage Major (single fatality and significant Possible High damage)

4. Poor installation Catastrophic (multiple fatalities and Unlikely High large scale damage)

Risk Treatment Options

Possible risk treatment options were generated for the High risks, commencing with Scenario 2 (Table 10.11). Scenarios 3 and 4 were addressed and additional options generated and short-listed (Table 10.12). The Medium risk, Scenario 1, was then reviewed. Risk

Table 10.11—Scenario 2 options

No

Prompt

Feasible option

Evaluation

1

Prevention

Horizontally drill from the plant to the valley beyond the village. (This eliminates much of the risk.)

Price and review

2

Prevention

Pressure test the line before burying. (This also reduces Scenario 4.)

Adopt

3

Prevention

Use line testing procedures that are thorough and enforced. (This also reduces Scenario 4.)

Adopt

4

Prevention

Maintain signage and other items agreed to protect the line from being accidentally damaged by digging.

Adopt

5

Prevention

Regular inspections — at least twice per week.

Adopt

6

Prevention

Give the villagers water. (Pipeline water is unsuitable for use; the company may have to generate potable water separately; this would introduce a new liability and risk.)

Discard

7

Protection

Install an outer sleeve.

Discard

8

Protection

Dig into rock and backfill with concrete.

Discard

9

Protection

Design extra thickness in the pipe wall such that the machines most likely to dig into the line are most unlikely to be able to penetrate it.

Adopt

10

Protection

Install a concrete slab over the line.

Adopt

11

Protection

Install warning tape in the trench between the slab and the surface.

Adopt

12

Protection

Dig to a depth of at least 2 m (the normal depth is 1 m).

Adopt

13

Mitigation

Construct a major water drain downhill of the line to prevent the water and mud from getting to the village.

Discard

14

Mitigation

Install a check valve (able to be pigged) downstream of the village.

Adopt

15

Mitigation

Install a second flow measurement device on the inlet to the tank at the end of the first pipeline section. On detection of a major leak shut down the pumps at the desalination plant.

Adopt

16

Mitigation

Install an alarm line above the concrete slab that if broken either raises an alarm at the desalination plant or automatically shuts down the pumps.

Review

treatment options were prompted in the areas of prevention, protection and mitigation to aid in generating a comprehensive list.

Scenario 1 will benefit from the extra pipeline wall thickness and the mitigation strategies recommended for Scenario 2. The horizontally drilled pipeline option could remove the pipeline from the area and eliminate the risk entirely.

Residual risk

The recommended actions for all four risks were considered effective in reducing the risks to tolerable levels. Table 10.13 shows the risk levels after taking all the actions marked Adopt, and after taking all those marked Review as well. Figure 10.4 shows the intended effects of the options on the design and installation of the pipeline.

Table 10.12—Additional options from other scenarios

Scenario

Feasible option

Evaluation

17 Scenario 2 Control the access to the inspection road and the Adopt pipeline route above the village, for example, with a fence and locked gates.

18 Scenario 2 Enhance the access road to make it a more accessible Adopt route for inspection.

19 Scenario 2 Inspect the valley area as part of the regular Adopt inspection.

20 Scenario 2 Include signage along the pipeline route with a Adopt suitable warning sign denoting the dangerous pressure and the fact that the water is industrial quality and unsuitable for agricultural or domestic use.

21 Scenario 2 Ensure that all the village is informed about the Adopt hazards associated with the water.

22 Scenario 2 Review the flow meters at both ends (option 15) Price and of the first section of the line and determine if it is review feasible to detect 50 mm, 25 mm and even smaller leaks.

23 Scenario 4 Specify a high quality of installation, inspection and Adopt testing prior to water being admitted into the line.

24 Scenario 4 Develop monitoring and line failure contingency Adopt plans when the line is first filled and pressurized.

25 Scenario 1 Sleeve the pipe such that a leak can be captured and Discard directed from the ends of the sleeve away from the village. There are some concerns about corrosion, inspection and effectiveness.

Table 10.13—Effect of actions on risk rankings for the pipeline failure scenarios

Scenario Initial risk Residual risk after Residual risk after Adopt and Review actions level Adopt actions i Natural disaster

Medium Medium

2 Accidental damage High Low

3 Wilful damage High Medium

4 Poor installation High Low

Low (a drilled line would not affect the village)

Conclusions

This case illustrates the level of detail that can be generated by a focused team in a short period, using an approach that covers all the main steps of the risk management process but in an abbreviated form. The assessment was simple to understand and the results were

Downhill to the village

Figure 10.4—Recommended options acceptable to the organization. There was no need for quantitative analysis, as the outcomes from the qualitative approach were quite sufficient for making the necessary decisions about the pipeline, its design and its route. Option 1, using horizontal drilling through the hill to avoid the risk altogether, had not been considered previously, and more detailed analysis of this option was planned.

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