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A Method of Determining Optimal Pipeline Residual Life

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A Method of Determining Optimal Pipeline Residual Life
There are consequences of the increase in investment in the extraction of hydrocarbon raw materials,particularly in
the exploitation of new oil,gas,and gas-condensate wells,and reduction in the number of shut-down and mothballed bore-
holes. The increase in the number of active wells requires the construction of new means of collecting hydrocarbons and mod-
ifying existing systems. The total length of oilfield pipelines exceeds 300 thousand km,and it is increasing.
This involves considering the best residual working life for oilfield pipelines from the viewpoint of absence of acci-
dents and ecological safety.
According to existing standards,the viability of a pipeline is determined by the safety margin on the tube material.
Correspondingly,the main way of determining the residual working life is to diagnose the pipes for hazardous defects:cor-
rosion pits,grooves,and other such defects that reduce the strength.
The working life as regards ecological safety can be estimated at the stage of planning measures to modify it or dur-
ing the determination of designs in the formulation of new pipelines. One can use existing statistical data on the failure dis-
tribution in pipelines in relation to working time [1],and also a criterion for the performance of measures to raise pipeline
safety [2].
The following failure probabilities (frequencies) have been given [1]:
• for major oil pipelines operated for up to 10 years,the failure probability (frequency) is (1.0–2.5)·10–3
per year
and per kilometer;
• for oil pipelines whose working time is in the range 10–15 years,the probability of failures is (3–5)·10–3
per year
and kilometer; and
• for oil pipelines whose working times exceed 15 years,the failure probability constitutes (5–20)·10–3
per year and
per km,and the statistical data indicate that the accident probabilities increase linearly with working times in the
range 15–30 years for product pipelines,with the accident probability constituting 20·10–3
for 30-year-old prod-
uct pipelines.
Experience shows that failures and accidents on oilfield pipelines are greater than on long-distance major ones.
However,to test this approach to ecologically safe operation working life,we use data provided for a major oil pipeline. This
statistical relationship between the failure probability and the working time is approximated with a reliability of more than
97% by
λ = 0.4477exp(0.195t),(1)
where λ is the failure probability in cases per km and year and t is the working time in years.
The criterion for the performance of measures that raise the ecological safety includes the cost necessary to imple-
ment a design as well as the risk level (a product of a probability of an accident and the calculated material losses) associat-
ed with that design:
K = (C/t
*
) + Ip + Cw + λL(Y + Ca – Is),(2)
Chemical and Petroleum Engineering,Vol. 40,Nos. 7–8,2004
A METHOD OF DETERMINING OPTIMAL
PIPELINE RESIDUAL LIFE
A. V. Kleimenov and G. L. Gendel’
SAFETY,DIAGNOSIS,AND REPAIR
VolgoUralNIPIgaz OOO. Translated from Khimicheskoe i Neftegazovoe Mashinostroenie,No. 7,pp. 34–36,July,
2004.
0009-2355/04/0708-0425 ©2004 Springer Science+Business Media,Inc. 425where K is that criterion in roubles/year; C represents costs of capital character or single occurrence related to implementing the
plan design in roubles; t
*
is the working time of the pipe after implementing the plan decision in years; Ip represents the insurance
payments consequent on existing legislation and contract with the insurance company in roubles/year; Cw represents the working
costs related to implementing the plan design in roubles/year; L is the length of the relevant part of the pipeline in km; Y is the
damage caused to the environment (calculated as the payment due to discharge of pollutants above the set limit for discharge of
pollutants, with a loading coefficient of 5) in roubles; Ca is the cost of eliminating the accident and its consequences in roubles;
and Is is the sum of the insurance cover due to existing legislation and agreement with the insurance company in roubles.
This definition implies that the criterion should be minimized for a given working time after the implementation of
a plan design. Also, one can compare the values for it only in relation to measures applicable to a particular object.
One uses statistical data on the rise in failure probability with working life to calculate the performance for a par-
ticular object in order to estimate the working time remaining for ecologically safe operation.
The basis is that a new pipeline is constructed in complete conformity with the statutory design requirements, the
materials used, the equipment, the methods of performing the constructional and installational operations, i.e., the technical
level of the new pipeline is acceptable and corresponds to minimal risk and retains its performance throughout the period of
its existence. Usually, the working life of a pipeline is taken as the time for its complete amortization, i.e., 33 years. Howev-
er, even if a pipeline is withdrawn from use in that period, it must have adequate ecological safety.
As an example of estimating the ecologically safe working residual life, we consider the passage of an oilfield con-
densate pipeline through a body of water of width 35–50 m. The condensate pipeline is operated for 15 years, has a nominal
diameter of 100 mm, and transports oil products of density 720 kg/m3
containing 1.5% by mass of hydrogen sulfide. The dis-
tance between the gate valves closest to the water is 2 km. The length of the part of the pipeline adjoining the water and slop-
ing towards it is 500 m.
The choice of this object is not accidental. Most petroleum organizations operate in areas with extensive river net-
works, and spills of oil products into water are accompanied by the maximum damage to the environment and the long-time
disruption of ecological equilibrium. In this example, there may be 6–10 tons of oil product escaping into the water with the
current means of observing leaks, and correspondingly the escape of 1.5–2.0 kg of hydrogen sulfide, which in most cases
destroys most of the natural inhabitants of small rivers.
Upgrades are the installation of stationary containing dams downstream and complete replacement of the water pas-
sage pipeline part. The one of these represents the initial state of the water crossing.
Fracture of the pipe body is a likely accident associated with oil products and dissolved hydrogen sulfide entering
the water. It is assumed that the working operators possess the necessary means of localizing an accidental spill and collect-
ing 40% of the oil products entering the water. The hydrogen sulfide is not removed. In the case of installing stationary con-
taining dams, the amount of oil products collected increases to 60%.
Table 1 gives the quantities needed to calculate the performance criterion for measures to raise the ecological safe-
ty for an oilfield condensate pipe passing through a water crossing. Figure 1 shows calculations on it in relation to the value
as affected by the period after implementation of the measures.
426
TABLE 1
Object upgrade C, roubles [3] Cw, roubles Ip, roubles Is, roubles Ca, roubles Y, roubles [4]
Initial state of water crossing – 15,000 30,000 1,000,000 897,000 3,117,000
Installing stationary containing structures 135,000 15,000 15,000 1,000,000 572,000 2,200,000
Replacing part of pipeline 675,000 15,000 10,000 1,000,000 897,000 3,117,000
Notes: 1. Failure probability λ defined by (1). 2. Ip and Is taken from rules for insuring the civil liability of organizations operating dangerous industrial
objects for causing injury to life, health, or property of third parties and the natural environment as a result of an accident at a hazardous industrial object
(confirmed by the All-Russia Union of Insurers 23 February 1998 and by the SOGAZ Insurance Society on 24 April 1998).The characteristic form of the curves is due to the capital costs (first term in (2)) decreasing with the passage of time,
but there is a sharp increase in the accident probability leading to a considerable reduction in the performance of the mea-
sures, a reduction in the ecological safety level, and an increase in the risk level (product of the sum of the quantities in paren-
theses in (2) and the accident probability as determined on the length of the condensate pipe).
Figure 1 shows that if the subsequent working period is less than 5 years, the realization of the proposed measures
to improve the ecological safety is ineffective. The object during that period retains a long expected life for effective support
to safe operation by comparison with other measures. Installing stationary blocking dams is desirable if the period of subse-
quent operation for the water crossing exceeds 6 years. If it is necessary for efficient and ecologically safe operation of the
pipeline at the crossing to be greater than 15 years, it is best to perform complete replacement of the pipes in that part.
The existing state of the pipeline after 19 years of operation exhausts the working life with the effective support to
the ecological safety level not less than the acceptable value, while installing dams in this example on operation over 20 years
enables one to attain the limiting performance by comparison with the acceptable level. Maximal and effective extension of
the ecologically safe working residual life at the water crossing may be provided by complete reconstruction.
The performance from replacing the pipes in the water crossing part by comparison with the initial state may be eval-
uated from the viewpoint of maximal extension of the working life for ecologically safe operation from the ratio of the accu-
mulated (total) number of years to the 33 years of operation represented by the performance criterion for the initial state and
the performance criterion for measures related to upgrading the pipeline, taken relative to the capital investments necessary
for the upgrading. The comparative performance constitutes more than 12 roubles per rouble of additional capital investment.
This approach can be employed at the planning stage to provide ecologically safe operation and enables one to esti-
mate quantitatively the optimum residual life for safe operation in production plant and to identify parts having what are
known in advance to be low or large residual lives, on the basis of objective characteristics in determining priority lines of
prophylaxis, diagnosis, upgrading, and development, as well as the most effective technical, organizational, and other mea-
sures that enable one to maintain an acceptable level of ecological risk.
REFERENCES
1. Yu. I. Pashkov, N. A. Makhutov, O. M. Ivantsov, et al., “Working life and safety of pipeline systems on the basis of
working time,” in: Problems of Safety in Emergencies, Issue 3 [in Russian] (2001), pp. 128–153.
427
Fig. 1. Dependence of the performance measure K in raising ecological safety
of condensate pipelines on the working life t
*
: 1) initial stage of water barrier;
2) installation of stationary limiting constructions; 3) replacing part of conden-
sate pipeline; – – – – level of effective provision of acceptable ecological risk.2. A. V. Kleimenov, “Planning measures to raise the safety of a production object on the basis of a quantitative per-
formance criterion,” Zashch. Okruzh. Sred. Neftegaz. Kompl., No. 7, 60–63 (2002).
3. Methods of Estimating the Damage from Pipeline Failures in the Oilfield Collection of Oil, RD 39-069-91, VNIISPT,
Ufa (1991).
4. Methods of Determining the Damage to the Environment from Accidents on Major Pipelines [in Russian], Trans-
press, Moscow (1996).
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