Case study – Transmission pipeline to UGS, Georgia
The UGS area at Ninotsminda is located approximately 40 km east of Tbilisi, on the southern part of the
Caucasus Mountains. The area has a changing topography with the highest point at an elevation of
approximately 1.200 m above sea level (or approximately 600 meters above the surrounding terrain).
The area has a history of natural hazards due to the large number of rivers in the area and the changing
topography.
The transmission pipeline to the UGS area is routed in a rural area, but will pass close to a number of
populated areas (e.g. Ujama, Ptardzeuli, Mukhrovani and Kalinovka), cross a number of rivers and cross
a number of roads. For some sections, the pipeline will run next to smaller roads.
The design parameters for the pipeline are:
-
operating pressure 80 bar
design pressure 110 bar
length 24 km
diameter 30’’ (760 mm)
wall thickness 8 mm
It has been discussed whether the transmission pipeline should be buried or exposed, but so far no
decision has been taken. In the risk assessment both of these options have to be taken into
consideration.
1/15
The transmission pipeline will be tied-in to an existing pipeline approximately 2 km east of Tbilisi. This
will be a very difficult operation, due to the fact that the gas company operating the pipeline would like
to limit the downtime and therefore the construction work as well as the preparations for the tie-in will
be carried out simultaneously as the existing pipeline is operated.
2/15
Exercise 1 – Risk identification (design)
You have been assigned the role as the project manager for the conceptual phase of the transmission
pipeline to the UGS area. Based on the description above, what hazards should be given special
attention in this early stage of the project?
To support the risk identification there are some working sheets presented below. Please use these
sheets to fill in the relevant information. Focus should be on the hazard and cause for the hazard with
considerations of the existing safeguards (only the first three columns in the worksheet)!
Should there be a need to assign an action of finding information related to the hazards, this is of
course allowed (e.g. investigate whether the gas could actually contain poisonous H2S) (the sixth and
seventh column in the work sheet).
3/15
Hazard
4/15
Cause
Existing safeguard
Consequence
Frequency
Risk level
Action
Responsible
Comment
Hazard
5/15
Cause
Existing safeguard
Consequence
Frequency
Risk level
Action
Responsible
Comment
Hazard
6/15
Cause
Existing safeguard
Consequence
Frequency
Risk level
Action
Responsible
Comment
Exercise 2 – Risk evaluation
As the project manager for the conceptual phase of the transmission pipeline to the UGS area you have
carried out a brief risk identification of the hazards that should be given special attention in this early
stage of the project, but how would you evaluate them in aspect of human safety?
It should be taken into consideration that a rupture of the transmission pipeline could give
consequences at several hundred meters of distance while small leakages from the transmission pipeline
only would give limited consequences.
To support the risk evaluations please make use of the work sheet from the previous exercise. A risk
matrix is also presented below.
Focus should be on the assessment of the frequency and consequence and the corresponding risk level
(column four through column six in the worksheet)!
Consequence
Severe
Significant
Moderate
Minor
Negligible
Unlikely
> 20 years
Remote Occasionally
Likely
Frequent
5-20 years 1-5 years 3-12 months 0-3 months
Probability/frequency
7/15
Exercise 3 – Frequency assessment
The original design of the transmission pipeline only included the actual pipeline. However, simulations
have shown that there might be some problem in keeping the operating pressure due to the length of
the pipeline. A process engineer proposed to include a simple pump station halfway for boosting the
operational pressure. This would also require increasing the wall-thickness in the transmission pipeline
to 12 mm for the closest 500 meters after the pump station.
As the project manager for the conceptual phase of the transmission pipeline to the UGS area you now
have to find out the increase in the total failure frequencies for the transmission pipeline due to the
incorporation of the pump station.
Total failure frequency (old)
Total failure frequency (new)
The components of the pump station and generic values for failure frequencies are presented below.
Component
Number/Length
Size
Failure frequency
Piping
Flanges
10 meter
8
30’’
30’’
1.4 x 10-6 per year-meter
2.1 x 10-6 per year-piece
Actuated valves
Instruments
2
4
30’’
-
1.1 x 10-5 per year-piece
2.5 x 10-5 per year-piece
Pumps
2
-
3.1 x 10-5 per year-piece
8/15
Component
Wall thickness
Failure frequency
Gas pipeline – onshore
X < 5 mm
5 mm < X < 10 mm
4.0 x 10-4 per km-year
1.7 x 10-4 per km-year
10 mm < X < 15 mm
X > 15 mm
8.1 x 10-5 per km-year
4.1 x 10-5 per km-year
Exercise 4 – Consequence assessment
The placement of the simple pump station was suggested halfway on the transmission pipeline, which is
located approximately 150 meters from a nearby village. The placement has caused objections from the
residents in the village based on concerns that a potential accident at the pump station could be
dangerous to them.
As the project manager for the conceptual phase of the transmission pipeline to the UGS area you now
have to find out whether an accident (jet fire) could be dangerous to the residents in the village. You
have conservatively chosen to study a catastrophic release (i.e. a hole with the diameter of 200 mm).
How long is the flame of the jet fire and how long is the distance to the level of radiation where we
could expect injuries also from short exposure (5 kW/m2)?
The rule-of-thumb formulas as well as consequence criterion are presented below.
Jet fire (flame length - meter)
𝐹 = 18.5 𝑥 𝑄 0.41
Jet fire (distance to radiation of 5 kW/m2 – meter)
𝐹 = 19.5 𝑥 𝑄 0.447
Where Q is the release rate (kg/s)
Release rate (kg/s)
𝑄 = 𝐴 𝑥 𝑃 𝑥 10−4
Where A is the leak area (mm2) and P is the pressure (bar)
9/15
Exercise 5 – Risk reducing measures
The detailed consequence assessments carried out by a consultant after the preliminary rule-of-thumb
formulas confirmed that there indeed was a possibility that the residents in the nearby village could be
affected by the different consequences (radiation from jet fire as well as flash fire from an ignited gas
cloud).
As the project manager for the conceptual phase of the transmission pipeline to the UGS area you now
have to find possible risk reducing measures that could decrease the risk for the residents in the village.
It should be noted that the risk could be decreased both reducing the frequency (i.e. how often) and the
consequence from the accident (i.e. how severe).
To support the identification and suggestion of risk reducing measures please make use of the work
sheet from the previous exercises (the sixth and seventh column in the work sheet).
10/15
Exercise 6 – Risk consideration
During the early stage of the project it has been discussed whether the transmission pipeline should be
buried or exposed, but so far no decision has been taken. In the risk assessment and risk evaluation
both of these options have been taken into consideration.
As the project manager for the conceptual phase of the transmission pipeline to the UGS area you now
have to establish a short list of pro’s and con’s for the different options of a buried transmission pipeline
and exposed transmission pipeline.
Focus should be on the additional hazards linked to the different options, but could also consider
operational aspects as well as potential increases and/or decreases in failure!
11/15
12/15
Buried – Pro’s
Buried – Con’s
Exposed – Pro’s
Exposed – Con’s
Exercise 7 – Risk identification (design life-time extension)
The transmission pipeline to the UGS area (including the pump station) was further developed in the
following FEED-phase and finally constructed in 2015. You received other duties and projects within the
company.
The transmission pipeline to the UGS area was designed with a design life of 25 years. Close to the end
of this period it was decided that the operation at the UGS area would continue and expand with
additional facilities. As a part of this project, a life-time extension study was initiated for the
transmission pipeline. Would it be possible to continue using the pipeline for another 15 years in the
current state?
It should be noted that only very limited maintenance have been carried out on the transmission
pipeline and that the latest internal and external inspection protocols are insufficient and outdated with
several years.
With your vast knowledge about the transmission pipeline you were assigned the role as the project
manager for the design life-time extension study.
The first task as the project manager would be to establish a list of information needed to start the risk
assessment as a part of the design life-time extension study (e.g. to identify what hazards have
changed and what additional hazards have arose during the design life-time of the transmission
pipeline).
13/15
14/15
15/15