ALINA
(Pipeline Leak Detection and Identification)
Introduction
OK-Solutions is now introducing our new service for pipeline leak detection (ALINA).
Hardware related leak detection methods (optic fibers, sensing lines, acoustic sensors, etc.) are
expensive. Alternative software methods are inexpensive but rely on flow measurements only.
With ALINA, we incorporate the use of hydraulic calculations and pressure measurements on
top of flow measurements. The advantage of our new service is that it not only detects but also
locates the leak for both gas and oil pipelines. A comparison between ALINA and leaks
detected via large flow discrepancies is provided in this report.
Background
A significant problem for pipeline operators is the formation of leaks along a pipeline. Because
a leak can lead to large losses of the product and environmental and property damage, the
pipeline must be examined to minimize leakage. Without a methodology or service, operators
can only rely on large flow discrepancies or visual inspection. If a leak is too small to be detected
from flow discrepancies or a thorough inspection is not scheduled for some time, it could remain
present from weeks to months leading to potentially millions of dollars lost. Leak detection
services provide a means to detect these smaller leaks; however, the time it takes to locate a leak
after detection may still lead to significant losses.
The service we provide operates with recently developed software based on data reconciliation
using pressures and flow measurements and the use of the generalized likelihood ratio. The
power of this method is related to the number of measurements and the precision of the
instruments used. The method can detect a leak of approximately 2% of total pipeline flow
within seconds or minutes, which prevents leaks from going undetected for long periods. The
most beneficial aspect of ALINA is that it detects the location of the leak, thus saving location
time.
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Benefits
1) Compared to just using large flow discrepancies (no software), ALINA can detect much
smaller leaks.
2) ALINA can predict the size of the leak. The power of ALINA (minimum leak size
detected) varies with the number and precision of the instruments used.
3) False positives are preventable. ALINA can distinguish leaks from biased instruments.
4) The largest benefit is the location of the leak. If a leak is detected, there are miles of
pipeline that the leak may be located. ALINA estimates the location of the leak, within
small distances (a function of the number of measurements and their precision) even for
small leaks. Thus, both time and money can be saved from locating a leak.
Assumptions
We now present a typical example: Table 1 displays all of the assumptions made pertaining to
this example analysis. The US average annual natural gas price is the average price for 2011.
(U.S. Energy Informaiton Administration)
Table 1. Assumptions for economic analysis
Pipe line network (miles)
Nominal Pipe Size (in)
Flow (Mscf/day)
Gas price ($/MMBTU)
Cost of locating leak ($)
Upstream Pressure (psia)
Downstream pressure (psia)
Distance between compressors (mi.)
Temperature, °F
Specific gravity
pipe material
Reynolds number (laminar flow)
Time to repair/clean
Time to locate leak(large flow
discrepancies)
6890
24
281,585
$3.95
$209,327
936
500
50
60
0.6
steel
2500
3 days
4 days
Analytical Methods
Leak Frequency
To analyze the economics, we assumed that the frequency of a particular leak size is proportional
to the probability of a leak size. Figure 1 depicts the number of times a specific leak size occurs
per year over 300,000 miles of pipeline. We assume that beyond ~10%, the leaks are large
enough that they are easily detectable by any means, and would lead to an emergency pipeline
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shutdown. This portion is not considered in this analysis. The frequency was determined using
significant incident data compiled by PHMSA.
Frequency vs leak size
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Frequency of leak
16
14
12
10
8
6
4
2
0
0%
2%
4%
6%
8%
10%
Leak size as a percent of total pipeline flow
Figure 1. Frequency of a leak versus the size of the leak as a percent of total flow
Pipeline Flow Rate
To perform this analysis, we also required the flow rate of the pipeline. For simplicity, we
assumed that a full pipeline network, both transmission and gathering for interstate and intrastate
pipes, of 6890 miles has a pipe size of 24 inches and a flow of ~280,000 Mscf. To calculate the
total flow in the pipeline, we used the following equation from the American Petroleum Institute:
Equation 1
Where Q is the volumetric flow of gas, d is the inside diameter in inches, P1 is the pressure at the
inlet, P2 is the pressure at the outlet, Z is the compressibility factor, T1 is the temperature at the
inlet, f is the moody friction factor, L is the length between compressors, and S is the specific
gravity.
Leak Detection Methods
For the large flow discrepancy method (FDM), we assume a minimum detectable leak size of
approximately 5% of the total pipeline flow. ALINA has a minimum detectable leak size of
approximately 2% of the total pipeline flow. These thresholds are based on instrument precision
and may vary from case to case, but ALINA is always lower than FMD.
Without any additional software or hardware, FMD can only detect a leak at its threshold; the
location of the leak narrows to the distance between compressors, usually measurable in miles, or
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flow meters. ALINA detects both the leak at its threshold and the location of the leak to a small
distance, measureable in meters. This saves time and money expended to locate a leak.
FDM is completely based on flow meters; any instrumentation error can lead to false positives or
a leak being undetected even at the threshold. ALINA uses both flow and pressure data,
allowing it to be more accurate and less prone to error.
Economics
Leak Costs
Figure 2 depicts the cost per day of various leaks sizes measured as a percent of pipeline flow
rate. It also indicates the leak thresholds for both ALINA and FDM. Below these thresholds, the
leak is undetected, meaning costs are unknowingly present.
$120,000
$100,000
Cost per day
$80,000
$60,000
Detection
Threshold for FDM
$40,000
$20,000
Detection
Threshold for ALINA
$0
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
Leak size as a percent of flow
Figure 2. Daily cost vs. leak size and thresholds of detection.
Figure 3 depicts annual costs as a function of leak size measured as a percent of total flow.
Below the thresholds of each case, cost is determined by the amount of fluid lost annually.
Above the threshold, the leak is detected and the cost drops because we assume the leak is
repaired. The new cost now is the cost of the leak for the small window it is present after being
detected. This varies depending on the method; ALINA locates the leak instantly while FDM
requires the leak to be located. We assumed it takes three days for a leak to be prepared. To
locate the leak once it is detected, we assumed it takes four days. The cost of locating the leak is
also taken into account.
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$25,000,000
Cost per year
$20,000,000
$15,000,000
$10,000,000
$5,000,000
ALINA
$0
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
Leak size as a percent of flow
Figure 3. Annual cost for ALINA and FDM
Table 2 depicts a comparison of the cost of the leak at 5% for ALINA and FDM. The predicted
time to repair the leak is assumed to take 3 days. FDM is divided into two cases dependent on
the time it takes to locate the leak. In case 1, the leak is locatable in 4 days while in case 2 it is
located in 7 days. The cost to locate the leak includes the cost of the leak being present for the
specified time-period and the cost associated with finding the leak estimated to be approximately
$200,000 annually.
Table 2. Leak repair and location cost comparison for ALINA and FMD at 5% leak size
Cost to locate and repair leak
ALINA
$150,000
-
Difference between ALINA and FDM
FDM 4 days
$598,000
FDM 7 days
$765,000
$448,000
$615,000
Expected Cost
To obtain the total annual expected cost for each method, integrate the product of the annual cost
and the frequency to determine the area under the curve. The area under the curve is equivalent
to the expected cost. The frequency of a leak size provided in Figure 1 is for 300,000 miles of
pipeline and needs to be considered for the network we are looking at of 6890. Thus, the
expected cost can be expressed as:
Expected Cost ($/year)
Equation 2
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Thus, the smaller the area below these curves, the smaller is the expected cost. Figure 4 shows
the curve formed from multiplying the frequency by the annual cost. The resulting expected
annual costs are provided in Table 3. As can be noticed, we expected savings of $1.7 million
dollars annually based on the thresholds assumed.
$1,000,000
$900,000
$800,000
Cost X Frequency
$700,000
$600,000
$500,000
$400,000
FDM
$300,000
ALINA
$200,000
$100,000
$0
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
Leak size as percent of total pipeline flow
Figure 4. Cost multiplied by frequency for ALINA and FDM
Table 3. Expected Annual Costs.
ALINA
FDM
Expected Annual Cost
$1,400,000
$3,100,000
Expected Annual Savings
$1,700,000
-
Conclusion
As this report indicates, a savings of $1.7 million dollars is possible with ALINA compared to
FDM possible for a 6890 mile pipeline network. This price can vary dependent on the frequency
of leaks (figure 1) and also on the thresholds of detection. ALINA can detect leaks, it can
determine the size of a leak, and it can determine the location of a leak within a small distance.
OK-Solutions can perform a free complimentary assessment for any system.
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