Engineering Justification Paper Lockerbie Offtake Full Site … · 2020-01-06 · pipeline from Lockerbie instead it only supplies downstream PRSs. There are more than 32,000 customers

Engineering Justification Paper

Lockerbie Offtake Full Site Rebuild/ Transmission Scotland - Network

Final Version

Date: December 19

Classification: Highly Confidential

2

1. Table of Contents

2 Introduction ........................................................................................................................................ 3

2.1 General Background ..................................................................................................................................... 4 2.2 Site Specific Background ............................................................................................................................... 4

3 Equipment Summary ........................................................................................................................... 6

4 Problem Statement ............................................................................................................................. 9

4.1 Narrative Real-Life Example of Problem .................................................................................................... 15 4.2 Spend Boundaries ....................................................................................................................................... 15

5 Probability of Failure ......................................................................................................................... 17

5.1 Probability of Failure Data Assurance ........................................................................................................ 18

6 Consequence of Failure ..................................................................................................................... 20

7 Options Considered ........................................................................................................................... 22

7.1 Option 1 Replace on Failure ....................................................................................................................... 23 7.2 Option 2 Repair on Failure .......................................................................................................................... 24 7.3 Option 3 Pre-Emptively Replace ................................................................................................................. 25 7.4 Option 4 Pre-Emptively Repair ................................................................................................................... 26 7.5 Options Technical Summary Table ............................................................................................................. 27 7.6 Options Cost Summary Table ..................................................................................................................... 28

8 Business Case Outline and Discussion ................................................................................................ 28

8.1 Key Business Case Drivers Description ....................................................................................................... 29 8.2 Business Case Summary ............................................................................................................................. 30

9 Preferred Option Scope and Project Plan ........................................................................................... 31

9.1 Preferred option ......................................................................................................................................... 31 9.2 Asset Health Spend Profile ......................................................................................................................... 31 9.3 Investment Risk Discussion ........................................................................................................................ 31

Appendix A – Acronyms ....................................................................................................................... 34

SGN Trans – 021Lock – EJP Dec19

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2 Introduction This intervention is one element of the Transmission Integrity programme within Scotland Network for RIIO GD2. The integrity programme is generally health driven considering the health of transmission assets - offtakes, local transmission system (LTS) pipelines, pressure reduction stations (PRS) and ancillary assets. ‘Health’ includes condition (corrosion, cracking, spalling etc.) and reliability (in-service defects etc.).

An Offtake is normally a Pressure Regulating Station which acts as the entry point to the Local Transmission System from the National Transmission System.

The primary roles of an Offtake are as follows:

• Filter the gas to at least 10µm • Fiscal Metering of the flow of gas conveyed through the site. This is required as an entry

point to the SGN network to determine the transportation charges to be levied by the company.

• Pre-heat the gas prior to pressure reduction to combat the effects of the Joule-Thomson effect

• Control the pressure of gas into the downstream pressure tiers whilst ensuring pressures do not exceed the Maximum Operating Pressure within the downstream system. This can be carried out on a pressure control basis (maintaining a certain downstream pressure) or a volumetric control basis (maintaining a certain volumetric flow rate with a combination of the control valves and meters).

• Odourisation of the natural gas exiting the site. This is a safety measure to ensure customers downstream can smell and report gas escapes when they occur. Metering is used to ensure the dosage applied is correct.

Filtration, pressure control, pre-heating, metering and Odourisation are typically designed in accordance with the Institution of Gas Engineers and Managers (IGEM) recommendations, IGEM/TD/13, Pressure regulating installations for natural gas, liquefied petroleum gas and liquefied petroleum gas / air.

The Offtake is required to be replaced as a part of the GD/2 programme of works. All primary assets within the station are to be replaced with the only exception being the Odourisation System. The chosen approach for this project differs from some other full site rebuilds in that the construction of the new assets are carried out entirely within the existing compound. This will require a phased replacement of the assets to be carried out within the compound due to limited space being available. The construction would take approximately 12 months.

The primary integrity drivers can be summarised as follows:

Table 1: Summary of the primary drivers for the full site rebuild of Lockerbie Offtake

Priority Key Drivers Comments

Primary Driver

Security of Supply

• Risk without compliant filtration. This site was modified by NTS for 85 barg uprating. This mod put filters after the regulators which is non-compliant with TD/13

• Fiorentini Regulators and Slamshuts have reliability issues. • Pipework or major component failure due to corrosion could seriously

compromise security of supply • More than 32,000 customers

Primary Driver

Condition and Safety

• Risk of component failure particularly release of stored energy from Swinney Filters.


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• Risk of high-pressure gas escape due to component failure

Secondary Driver

Lack of Pre-Heating

• Without any pre-heating there is no possibility of being able to pressure reduce downstream pipeline

• Defect Management is difficult without the ability to pressure reduce.

This Engineering Justification Paper explains the evidence and methodology behind the rebuild of Lockerbie Offtake being the recommended intervention.

The full rebuild of Lockerbie Offtake is an SGN named Offtake full rebuild project in Scotland Gas Networks as a part of the Pressure Control Integrity programme. It has a capital investment value of £1.736m please refer to section 7.7 for the detailed costing breakdown.

This Lockerbie Offtake rebuild is required due to an unacceptable risk to security of supply compounded by various factors. A full rebuild has been identified as the only acceptable engineering solution due to both the inadequate operation of existing equipment and defects identified on site. This is also an opportunity to integrate pre-heating into the design of the site which will bring integrity to the entire downstream pipeline as explained in the rest of the paper. This is further justified by the CBA produced for this project.

2.1 General Background This site is located North of Lockerbie and was commissioned in 1977 (42 years old as of 2019). The site comes off the NTS at a Maximum Operating Pressure of 85barg and its HP regulator skid regulates the pressure down to 69 barg. There are no direct customers fed from the downstream pipeline from Lockerbie instead it only supplies downstream PRSs. There are more than 32,000 customers downstream from Lockerbie Offtake that rely on this station for their gas supplies and the Offtake is a single feed into the system.

There are 6 PRSs connected to the downstream pipeline namely: Dumfries (Heathhall), Lochmaben (Hallmuir), Milton, Newton Stewart, Priestdykes, and Rhonehouse.

2.2 Site Specific Background Lockerbie Offtake is in the council area of Dumfries and Galloway which is in the Western Southern Uplands.

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The site, which extends to some 5,200m2, and was commissioned in 1977 as a part of the construction of the Local Transmission System which was a part of facilitating the conversion to supplying dry natural gas. To this day, Lockerbie Offtake serves the purpose of feeding the LTS “M System” pipeline which supplies for more than 32,000 customers.

Due to the reliability issues with the pressure control equipment which is non-compliant with TD/13, safety concerns with on site assets and lack of pre-heating on site Lockerbie Offtake has been selected for a full site rebuild as a part of the ‘Pressure Control Integrity Programme’

3 Equipment Summary Lockerbie Offtake is one of 18 Offtakes in Scotland’s Network

Lockerbie Offtake is in many ways a typical ‘TD/13’ configuration consisting of filtration, pressure control, metering and odourising.

As typical for PRSs and Offtakes redundancy is utilised:

• The Filters have redundancy with one additional filter in a separate stream

• The Regulating Streams have redundancy with one additional stream and one additional regulator per stream.

This site did not originally require any pressure regulation as the upstream NTS system and LTS downstream operated at the same pressure. In 1998 a Pressure Regulating Skid including components supplied by Fiorentini was installed to accommodate the uprating of the National Transmission System to 85 Barg. No significant Asset Health Capital Investments have been carried out since these works.

Lockerbie Offtake is atypical regarding the relative positions of the pressure regulating skid and metering. Filtration would normally occur before pressure control to protect any soft parts from any debris within the system. However, due to Lockerbie Offtake being adapted to accommodate the uprating, NTS installed the pressure control before the filters. This reduces the protection that the pressure control skid has from debris but will be rectified by the full site rebuild.

The filters which were installed in 1977 during site construction are 2 x 200NB SPX (Swinney) –Models. The Primary Protective Devices are 2 x 150NB Fiorentini – SPC/782/105 (spring actuated valves) which were installed in 1998 but are now obsolete (unsupported without spares). Pressure control is provided by 4 x 100NB Fiorentini Reflex 919 Regulators which were also installed in 1998. Metering is provided by an Energy Systems- Measure Master type Orifice Plate which was installed in 1977 and is original to the site.

Table 2: Key Attributes for Lockerbie Offtake PRS Attribute Details

Potential Peak Demand (Source, Winter Ops Plan 18/19)

34,100 scmh

Inlet Maximum Operating Pressure

85 barg

Outlet Maximum Operating Pressure

69 barg

Regulation Control Type Pressure Control


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Stream Configuration Stream A Working: 2 x Regulator [Active + (Monitor/ Rough Cut)] Stream B Stand-By: 2 x Regulator [Active + (Monitor/ Rough Cut)]

Table 3: Lockerbie Offtake Equipment Summary PRS Equipment Details Commissioning Year

Filter Details 2 x 200NB SPX (Swinney) 1977

Regulator Details 4 x 100NB Fiorentini Reflex 919 Regulators 1998

Primary Protective Device Type

2 x 150NB Fiorentini SBC/782/105 Slamshuts 1998

Meter Details 1 x 200NB Energy Systems Measure Master 1977

View of the primary assets in Lockerbie Offtake

In figure 4 the Pressure Regulating Skid as installed in 1998 to enable the uprating is shown. The Fiorentini Reflux 919 Control Valves uses a large diaphragm and spring to control the opening of the orifice and the flow of the gas downstream. This is more like regulators typically used for low pressure applications.

The Fiorentini – SBC/782/105 Slam Shuts uses the combination of a sensing pilot, latching mechanism and spring-loaded closure to shut in the event of over pressurisation of the downstream system.


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Lockerbie Offtake Main Pressure Regulating Skid

Odourisation System which will be retained following the full site rebuild


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4 Problem Statement Why are we doing this work and what happens if we do nothing?

It is proposed to carry out a full site rebuild of Lockerbie Offtake within the existing Site Compound.

The decision to rebuild Lockerbie Offtake will rectify integrity issues with condition and operation with equipment which currently compromise the safety and security of supply with the site. Unsupported and unsuitable Fiorentini Pressure Control Components will be replaced by fully supported equipment which will be determined by a robust tendering process. This will eliminate the risks caused by a lack of spares availability. In addition, the decision to rebuild the site will allow pre-heating to be integrated into the system to protect the downstream pipeline when pressure reduction needs to be carried out.

The Fiorentini SBC/782/105 Slamshuts are on the left one tagged 432529 and the

Fiorentini- Reflex 919 Regulators are on the right one tagged 432531

As described in the equipment summary, the Fiorentini Slamshuts have similarity in their operation to the Tartarinis. Unlike the Tartarinis, these Fiorentini Slam Shuts are unsupported with no availability of spares. Furthermore, these specific models have operated out of acceptable tolerance multiple times during PSSR inspections. During an over pressurisation scenario there is an expectation for the slamshut to close within a reasonable period. These slamshuts have had repeated issues closing out with the time limits defined by the WSoE and SGN Standard PS/3. A2 faults have been raised multiple times with unsuccessful attempts to permanently resolve the slow firing time.


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Table 4: Historical PSSR results for one of the Fiorentini Slamshuts Parts Reference 432529 PSSR Fault Classification Frequency of occurrences since 2002

A1 0

A2 29

B 4

C 8

Lockerbie Offtake Swinney SPX Filters (200 NB)

As with all Primary High Pressure Filters the Swinney Filters at Lockerbie Offtake undertake an ES/94/15 part 2 inspection as described in PS/3. Among other checks, this inspection involves Magnetic Particle Inspection as a method of detecting any “crack like defects” within the filter. In 2017 linear features were detected on the filters which were identified as “surface casting defects”. While not definitively identified as “cracks”, these defects require periodic monitoring to ensure that they do not propagate any further.

Furthermore, there are no available spares for the closure mechanism of these filters. This severely limits options when the mechanism has any critical defects.


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An example of the Joule-Thomson effect on downstream pipework. Note the icing

occurring on the surface of the pipework.

Another important driver for this project is the lack of pre-heating on this site. The maximum theoretical cut in typical operation is from 85 barg to 70 barg (and this cut would typically be much lower) which does not necessitate the use of pre-heating much of the time. However, as a part of the P/11 procedure a pressure reduction may be required on the Dumfries Transmission System if a defect was to be a discovered until it is resolved. If a pressure reduction to 50% of the MOP was necessary in a peak flow condition this would result in very negative temperatures. Although the conditions are unlikely to be this severe, the reality is that it is not possible to carry out pressure reductions on sections of the downstream network for extended periods of time without subjecting the pipe to unacceptably low temperatures. Installing pre-heating will provide a contingency against these scenarios.


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Energy Systems - MeasureMaster Orifice Plate (200NB)

In addition to these mechanically driven upgrades, E&I Network have identified obsolete equipment that could be replaced concurrently.

With the existing Orifice Plate based metering system at Lockerbie Offtake there is a greater potential to reach non-compliance of the measurement uncertainty at the bottom end of the system measurement range below 10% due to the measurement system relying on differential pressure which falls off at low flow conditions. There is a process underway to connect a Biomethane site to the network that Lockerbie energises. Experience has demonstrated that low flow will become a more frequent occurrence when Biomethane sites join the network.

Newer meter systems such as the Ultrasonic metering (USM) that will be installed at Lockerbie Offtake is better able to cope with a wider range of flow rates without exceeding uncertainty of measurement tolerances (+/- 1% volume and +/- 1.1% energy).

The proposed new USM metering systems have inbuilt diagnostic capability and increased scope for condition-based monitoring of the measurement system with earlier warning of problems possible. The USM meters have multiple path sensors providing an improved measurement certainty across the meter and gas path. Flow conditioners have also been added to further improve the uncertainty of measurement possible and thus provide improved accuracy of the overall system.

The decision to do nothing is not permittable due to risks to security of supply and safety.

An inability for SGN to resolve the existing defects associated with pressure containing plant constitutes a failure to comply with PSSR and the Health and Safety at Work Act.


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The lack of supported pressure control equipment or the provision of pre-heating renders the existing Offtake not “fit for purpose” for the long-term purpose of supplying gas. The combination of the previously discussed issues results in a modelled risk of failure that will continue to increase steeply without enough capital investment.

The accompanying Cost Benefit Analysis gives further justification for carrying out this work.

What is the outcome that we want to achieve?

This capital investment will be considered a success if the full site rebuild of Lockerbie Offtake can be delivered within budget and the allotted programme. CBA benefits will be realised as soon as the new site is commissioned. The design life of the new site will be for a minimum of 40 years, with all previously described integrity issues addressed. The tentative proposal is to construct the site in accordance with as represented below in the draft drawing which has been produced by the designers of the new site:

How will we understand if the spend has been successful?

As a part of SGN’s internal investment review process we look at the benefits incurred by a project by a process called the Post Investment Appraisal. The criteria used to measure this are known as

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the PIA success criteria. This has been replicated below to show how to understand whether the spend is successful for the GD/2 Integrity Programme.

Table 5: Post Investment Appraisal Table Lockerbie Offtake Ref 1 2 3 Benefit Description Ensure the benefits

are SMART and establish if they are

Tangible or Intangible.

Reduction of Monetised Risk as recorded part of the CBA. Tangible

Full Site Rebuild of Lockerbie Offtake delivered within budget and agreed timescales. Tangible

Site operated by fully supported equipment (no obsolescence) Intangible

Delivery Mechanism Describe what will

enable the benefit(s) to be released –

what are the project Outputs.

Benefit will be realised through the full site rebuild of Lockerbie Offtake which will be carried out in a phased manner.

Baseline Measurement

· What is the current baseline

measurement · Who will carry

out the measurement

· What tools, techniques,

processes are used

The current baseline measurement is the projected risk increase without intervention. This is explained fully in sections 5 and 8 of this plan. This will be carried out by the Senior Data Analyst in Asset Management. This is modelled through the

Monetised Risk Software.

The baseline measurements are the project budget and agreed timescale. Finance, Major Projects and Asset management will carry out the monitoring. The project finances are monitored through SGN finance systems. Timescales are monitored through Microsoft Project and the Plant/1 process.

The baseline measurement is the current site which has unsupported E&I equipment in addition to unsupported Slamshuts.

Benefit realisation plan: How much will

be released and when

The full benefits of the reduced monetised risk and CBA will be realised as soon as the new station has fully been commissioned. As the rebuild is being carried out and commissioned in a phased manner some of the benefits will be realised gradually.

The benefits of delivering the Lockerbie Offtake Full Site Rebuild on time and on budget will be released as a part of being able to deliver the entire GD/2 Programme.

As soon as any obsolete assets within Lockerbie Offtake have been decommissioned and replaced with supported assets these benefits will be realised.

Owner: Who will be accountable for delivering the

realised benefit

Major Projects and Asset Management

Benefit realisation measurement: How will the value of the

actual benefit be measured Who will

carry this out

The value of the benefit will be measured by modelling the reduction of monetised risk in C55 by the specific interventions carried out. This will be carried out by the Senior Data Analyst in Asset Management.

Finance and Major Projects will monitor the financial benefit through our internal finance system. The Plant/1 Process and Microsoft Project can also be used to verify the project has been completed within the identified timescales.

Asset Management and Maintenance will realise the benefit in both the reduced likelihood of parts replacement being required and the actual availability of spares in using fully supported equipment.

Commercial Confidentiality


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4.1 Narrative Real-Life Example of Problem Kirkcaldy PRS is a site located in Fife that supplies gas to nearly 25,000 customers in the town of Kirkcaldy. This site had a particularly severe issue associated with the condition of the filters and numerous crack like defects being discovered. The inspections that discovered these issues designated both filters of having A2 condition and not being suitable for being commissioned. This resulted in a full replacement of both filters having to be carried out.

Photo from Kirkcaldy PRS Filter Inspection

Through continued service imperceptible defects that were likely present since manufacture propagate and grow until they become risks to the integrity of the filter. Due to both filters not being suitable for continued service this replacement had to be carried out quickly while using temporary methods for filtration with no redundancy. Pre-emptive replacement of the filters at Lockerbie will prevent this being a risk at this location.

4.2 Spend Boundaries This Project is for a Full Site Rebuild of Lockerbie Offtake connected from the existing Block Valve installation within the site. Almost every Mechanical and E&I Asset will be replaced because of this project with the only key exception being the Odourisation System. The scope for this project has been well developed because the detailed design has already commenced. The following is included within the scope of the project:

Primary Mechanical Assets:

• 200NB Class 600 Ball Valve from Block Valve Installation to act as the new inlet to the site


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• Twin Stream Above Ground Filter Skid on a new concrete base • Twin Stream Above Ground Ultrasonic Meter Skid • Package Boiler House and Heat Exchangers to provide pre-heating as a contingency to protect the

downstream pipeline. • Twin Stream Regulator Skid Unit. This will utilise Control Valves due to the inlet and outlet

pressure being equal most of the time. In these circumstances no throttling of the gas is required. • Interconnecting pipework to convey the process flows • New Outlet Pipework to connect to the existing pig trap facility

Primary Electrical Assets:

• Retained Assets to be Transferred to New Control Building

• LGT gas treatment panel • LGT/FWACV UPS System • Site security system complete with integral UPS and 1:1 transformer • CP TR system • 24V PSU and battery (if capable) • PI-1 signal from inlet

• E&I Assets to be retained

• Three phase distribution • Outstation (RTU) with DB1 system • Barriers with galvanic P&F LB barrier systems • FWACV rack

• E&I Assets to be installed new

• Metering system with ultrasonic meters • Metering cubicle • Analyser cubicle • On site GRP and PRU cabinets • DP cubicle • Inlet and outlet pressure transmitters • Both filter differential pressure transmitters and filter differential pressure switch • 1:1 transformer • Generator changeover system • New instrumentation loops (transmitters/switches/cables) • New ducting as required

A capital investment value of £1.736m will be required for this project in GD/2. A detailed breakdown of these costs can be found in section 7.7.

Within GD/1 £0.430m of expenditure is expected for design and materials to aid the delivery of this project in GD/2.

The following is not included within the scope of this project:

• Replacement of the NTS Block Valve Installation • Replacement of the Odourisation System • Replacement of the Pig Trap Facility


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5 Probability of Failure When considering the possible failure modes that could occur on Lockerbie Offtake, there are a few different categories in which these failure types can be grouped. A couple of the most credible forms of failure on Lockerbie Offtake are discussed in detail below:

Release of Gas

• Pressure Containing Component within site (Corrosion or Crack Propagation): This failure mode is of the type when a gas escape is caused by excessive deterioration of a pressure containing component. The probability of this failure occurring is increased by the deteriorating condition of the pressure containing assets. Lockerbie operates at a high-pressure tier with an inlet MOP of 85 barg and an outlet MOP of 69 barg which would increase the severity of such an occurrence. Lockerbie Offtake has Filters with increasing risk of life limiting defects. If a failure was to occur on the filters the pressure at the point of failure could be as high as 85 barg.

High Outlet Pressure

• Pressure Regulating Equipment (Over pressurisation of Outlet System): This is the failure mode caused by the failure of the Regulators and Slamshuts to restrict the outlet pressure and prevent it being increased above the outlet system’s design parameters. Sites with evidence of regulator or slamshut control issues from inspections will have a higher probability of failure. As previously discussed the Fiorentini – SBC/782/105 Slamshuts have failed to close in a reasonable period.

By extracting asset attribute data from C55 it is possible to determine likely quantity of equipment failures within a given system within a single year. This can be summarised for each asset system in the table below:

There is no pre-heating system currently on Lockerbie Offtake.

Table 6: Lockerbie Offtake Pressure Control Failure Rates for a Given Year Pressure Control

Failure Mode 2021 2022 2023 2024 2025 2026 High Outlet Pressure 0.19 0.19 0.21 0.23 0.26 0.29 Low Outlet Pressure 0.00 0.00 0.00 0.00 0.00 0.00 Release of Gas 0.01 0.01 0.01 0.01 0.01 0.01 General failure 0.03 0.03 0.03 0.03 0.04 0.04

Table 7: Lockerbie Offtake Filter Failure Rates for a Given Year Filter

Failure Mode 2021 2022 2023 2024 2025 2026 High Outlet Pressure 0.00 0.00 0.00 0.00 0.00 0.00 Low Outlet Pressure 0.00 0.00 0.00 0.00 0.00 0.00 Release of Gas 0.01 0.01 0.01 0.01 0.01 0.01 General failure 0.03 0.03 0.03 0.03 0.04 0.04

The methodology around these failure modes is explained in section 5.1.


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5.1 Probability of Failure Data Assurance Data Assurance is provided through the NARMs methodology and the method of using theSystem to calculate monetised risk values and their impacts on the CBA. Please see an explanation of this and the specifics that apply to Lockerbie Offtake:

Background

The failure rate and deterioration applied to calculate the CBA is consistent with the NARMs methodology. The key principle adopted in the methodology to facilitate the assessment of risk are:

• Asset health equates to the probability that the asset fails to fulfil its intended purpose and thus gives rise to consequence for the network.

• The consequences can be assessed in monetary terms

• The risk is determined from the product of the number of failures and the consequence of those failures

Diagram showing Monetised Risk Methodology

Failure rate

In the NARM framework ‘failure rate’ is used to calculate the Probability of Failure. The failure rate gives the rate of occurrence (frequency) of failures at a given point in time and may also include an age/time variable, known as asset deterioration, which estimates how this rate changes over time. The failure rate can be approximated by fitting various parametric models to observed data to predict failures now and in the future. Therefore, data that contributes towards monetised risk value has been thoroughly reviewed for each system under this investment.

Failure modes

In the NARMs methodology the failures are categorised into different Failure Modes. Below is list of all failure modes considered in the methodology and any data modification made to the model.

Pressure control and Filter • Release of Gas - relating to the failure of a pressure containing component on site leading to

an unconstrained release of gas within and possibly off the site • High Outlet Pressure - failure of the Pressure Control system to control the pressure at least

to within the Safe Operating Limit of the downstream system. This would typically require the concurrent failure of both regulators and the slamshut (failure to operate) within one Pressure Control stream.

• Low Outlet Pressure - relates to the failure of the Filter and Pressure Control system to supply gas at adequate pressure leading to partial or total loss of downstream supplies

• Capacity - where the system has insufficient capacity to meet a forecast 1:20 peak day downstream demand



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• General failure - relating to other failures not leading to either a safety, environmental or gas supply related consequence.

SGN’s NARM’s model has been developed based on methodology agreed for all networks with Ofgem which uses requires a set of base data. The base data for this site was originally the output of a data collection exercise conducted in 2011 and has been reviewed to more accurately reflect the current position. Any changes are summarised in the tables below.

The below table shows any attribute material changes required for the Pressure Control System of Lockerbie Offtake. The justification for this is obtained from the detailed consideration of any inspection, fault counting or other data.

Condition Change:

Table 8: Material changes for the Pressure Control System of Lockerbie Offtake Pressure Control

Asset Attributes Modification Reason

CONDITION_SCORE Changed from 3 to 4

Slamshuts are Fiorentini SBC/782/105 which in addition to having reliability issues, have no ready availability of spares. This makes it difficult to resolve any operational issues which require replacing components in a timely manner.

Slamshuts have reliability issues in relation to speed of response/operation. This has resulted in frequent A2 results during testing on functional checks.

HIGH_OUTLET_PRESSURE

Changed from 5 to 3.8

The slamshut on site has multiple A2 faults raised against it due to the slow closer of the valve which could potentially lead to high outlet temperature. In total there has been 23 A2 faults raised over the last six years.

The below table shows any attribute material changes required for the Meter System of Lockerbie Offtake. The justification for this is obtained from the detailed consideration of any inspection, fault counting or other data.

Table 9: Material changes for the Filter System of Lockerbie Offtake Filter



Both filters exhibit crack-like defects which are being periodically reviewed to ensure no propagation occurs. Monitoring of these defects is ongoing.

The below table shows any attribute material changes required for the Filter System of Lockerbie Offtake. The justification for this is obtained from the detailed consideration of any inspection, fault counting or other data.


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Table 10: Material changes for the Metering System of Lockerbie Offtake Metering



Orifice plate’s exhibit high uncertainty and poor turndown ratio when compared to ultrasonic metering. This has various consequences as follows:

Safety - Under-Odourisation may lead to undetected gas leaks whereas over-Odourisation may lead to an increase in public reported escapes (PREs).

Commercial - Measurement with high uncertainty may result in large losses or gains in financial terms and may also lead to an increase in network Shrinkage.

Operational - Control of the system may be difficult when operating at low flow rates with high uncertainty or no visibility (i.e. below low DP cut-off).

Condition of metering is moderate

6 Consequence of Failure When assessing the credible failure modes for Lockerbie Offtake, there are a few categories of consequences to consider.

The below Matrix plots the credible failure modes against how severely it will affect each of the consequences. These are colour coded to give a visual representation of the likely impact:

Table 11: Matrix of Failure Mode against Failure Consequence for Lockerbie Offtake

Failure Consequence

Failure Mode Loss of Supply to Customers Safety Impact Environmental

Impact Failure of High-Pressure Filters due to propagation of a “crack like defect”

If gas escape is significant, security of supply could be affected

Risk of harm for release of stored energy from pressure vessel. In addition, the risk of ignition/asphyxiation.

Carbon emissions proportionate to the volume of the escape

Pressure Regulating Equipment Failure (Over pressurisation of Outlet)

A major rupture on the sole pipeline feeding 32,000 customers would have severe effects on security of supply

Safety impact is elevated compared to escape within the site, as the LTS pipeline is at proximity with the public with points.

Carbon emissions proportionate to the volume of the escape

Loss of Supply to Customers

Except for some minimal interactivity with Langholm Offtake on the network downstream of the Lochmaben site, the outlet pipeline from Lockerbie codenamed the ‘M system’ is a single source supply to more than 32,000 of the customers it feeds through 6 PRSs.


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A major failure at Lockerbie Offtake would result in the failure to supply gas to more than 32,000 customers. In terms of ‘unplanned interruptions costs’ SGN would compensation costs of £960,000 for every day that gas supplies are not restored.

Safety Impact of Failure

A gas escape caused by a failure either within Lockerbie Offtake or on its outlet system could have safety implications on anyone in proximity.

Natural Gas holds a few primary risks in this regard:

• Risk of burns from ignition

• Risk of injury from dangerous release of pressure energy

• Risk of asphyxiation from natural gas depleting the oxygen in the environment

The impact of aging and pressure cycling on filters increases their risk of failure and reduces the ability for these risks to be managed appropriately with time. SGN has the obligation to reduce these risks as low as is reasonably practicable under the Health and Safety at Work Act.

In addition, SGN has obligations to protect members of the public from the risk of harm caused by failure of infrastructure under the Pressure Safety Regulations. SGN must ensure that its pipeline do not operate under conditions they were not designed for (e.g. excessive pressure).

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Environmental Impact

SGN is required to pay penalties for significant gas escape incidents which is proportional to the volume released into the atmosphere. This is due to SEPA, Scotland’s principle Environmental Regulator implementing an Enforcement Action resulting in a fine.

The value of these penalties is determined by the societal impact of the carbon that has been released. When compared to Carbon Dioxide, Methane has a global warming potential 104 times greater over a 20-year timeframe. The same comparison over a 100-year period shows a 28 times greater impact than Carbon Dioxide.

These figures illustrate how SGN’s goal of successfully transporting natural gas to end users to be burned and produce carbon dioxide is preferable to allowing the natural gas to escape to atmosphere on an environmental basis (this is of course a separate argument to alternative sources of heating homes). Therefore, SGN has great interest in minimising leakage in its network as far as possible.

The cost of carbon has been included within the monetised risk modelling within the accompanying CBA.

7 Options Considered Within this Engineering Justification Paper for there are 4 options which have been considered and discussed to address the integrity issues on Lockerbie Offtake. The 4 core options being considered are as follows:

• Replace on Failure • Repair on Failure • Pre-Emptively Replace • Pre-Emptively Repair

When considering this intervention, we have done so following our 4R strategy. This strategy is designed to maximise the asset life and minimise the capital expenditure of intervention and in doing so sets out an order of preference for the intervention type. This order is key in delivering customer value and focuses on the lighter intervention options of repairing and refurbishing the asset before considering more severe interventions such as full replacements of the existing assets.


23 December 2019

See figure 14 below for an illustration of our 4R strategy:

Diagram of 4R Strategy. Repair and Refurbish options at the top are considered before resorting to Replace or Rebuild at the bottom

Following this strategy, the options of a reactive repair or proactive refurbishment are considered ahead of proactively rebuilding the site or carrying out a replacement reactively.

However, an assumption of being able to choose a reactive option would be to be able to accept the consequences of a failure while implementing the remediation, whether it is a repair or a replacement. Whether this approach is merited for a national offtake with a large customer base is discussed in sections 7.1 and 7.2.

Proactive approaches for Lockerbie Offtake are discussed as an alternative to waiting for a failure. These too can be carried out as either a repair or replacement, with repair being prioritised as a better value option providing it is technically feasible. To qualify as a comprehensive repair, it would need to address every issue discussed within the Problem Statement. The option to carry out a pre-emptive full site rebuild of Lockerbie Offtake has been assessed to return an expected NPV of £8.37m by FY 56/57 . This is discussed further within sections 7.3 and 7.4.

7.1 Option 1 Replace on Failure Technical Detail

The scope for this option is for the various components/asset groups within Lockerbie Offtake to be replaced at the point of failure. For example, if a regulator/slamshut skid was to fail as caused by the equipment not being reliable, the pressure regulating equipment would be replaced at this time.

The technical detail of the replacement would be dependent on the actual failure that has taken place. The specifications of the components being installed would be the same as for the pre-emptive full site rebuild. Specific components that would be replaced is the only aspect that would change depending on which component has failed.


24 December 2019

Basis of Costing

The consequences of a failure such as this would be complete loss of supply to more than 32,000 customers. There are various credible non-trivial failures on Lockerbie Offtake that could occur which have been previously explained within this paper. It is therefore not technically feasible to proceed with this option as a failure of this nature is unacceptable. Consequently, a comprehensive costing for this option has not been carried out.

Benefits of Option

The benefits of option 1 include the fact that capital investment would be highly focused on the specific asset that had failed. The smaller scale of project would also reduce the potential risks/uncertainties when compared to a full site rebuild.

However, these benefits are completely overwhelmed by the negative consequences of a failure occurring (see section 6 ‘consequences of failure’). In certain cases where the replacement could be carried out quickly due to the specific component being easy to install and most of the equipment being procured in GD/1. However, even if a replacement could be carried out in a matter of days the negative consequences of having lost over 32,000 customers would still be sustained. As previously outlined, financial losses would represent almost £1,000,000 a day before the operational costs of relights have even been considered.

Delivery Timescales

The delivery timescale of this option is highly dependent on the nature of failure that has occurred. It could vary from several days to potentially months.

Key Assumptions

For this option it has been assumed if a failure were to occur that would be operationally feasible to carry out a replacement to address any failure.

Even with this assumption, this option is not considered technically possible due to consequences sustained from a failure.

Unique Aspects of Option

The unique aspect of this option is that it is the only one that proposes using full replacements to address failures without pre-emptively carrying them out to prevent the failure in the first place.

7.2 Option 2 Repair on Failure Technical Detail

The scope for this project is for the various components/asset groups within Lockerbie Offtake to be repaired at the point of failure.

The specific technical details behind the work required is not knowable as it is dependent on the nature of failure that has occurred. It is therefore difficult to plan for this type of option.

Basis of Costing

The consequences of a failure such as this would be complete loss of supply to more than 32,000 customers. There are various credible non-trivial failures on Lockerbie Offtake that could occur which have been previously explained within this paper. It is therefore not technically feasible to proceed with this option as a failure of this nature is unacceptable. Consequently, a comprehensive costing for this option has not been carried out.


25 December 2019

Benefits of Option

The benefits of option 2 include the fact that it would potentially involve a lower capital investment to address a failure. It also represents an attempt to maximise the operational life of the existing assets.

Again, these benefits are completely overwhelmed by the negative consequences of a failure occurring (see section 6 ‘consequences of failure’). Even with the generous assumption that a repair for the specific failure is possible, as with 7.1 the very occurrence of a failure will bring all the severe consequences with it.

Delivery Timescales

These are highly dependent on the nature of the repair, but if a repair is considered as practical it is assumed it could be carried out in a fairly short period of time (matter of days).

Key Assumptions

To even allow this option to be considered, it has had to be assumed that it is even possible to carry out a repair that will allow a site to be re-commissioned following a major failure.


The unique aspect of this option is that is the only one that relies on repairing equipment that is potentially more than 40 years to continue service following an incident.

7.3 Option 3 Pre-Emptively Replace Technical Detail

Section 4.2 explains in some detail the scope of the investment for this option.

To summarise, this option is for a full site rebuild of all the primary assets within the site between the block valve installation on the inlet and the pig trap installation on the outlet.

Table 12: Key Attributes for Replacement Lockerbie Offtake PRS Attribute Details

Design Peak Demand 46,800 scmh

Inlet Maximum Operating Pressure

85 barg

Outlet Maximum Operating Pressure

69 barg

Regulation Control Type Pressure Control (Control Valves)

Stream Configuration Stream A Working: 2 x Regulator [Active + (Monitor/ Rough Cut)] Stream B Stand-By: 2 x Regulator [Active + (Monitor/ Rough Cut)]

Basis of Costing

• Due to procurement taking place in GD/1 Materials Costs are based on known costs occurring purely in GD/1.

• Planning Application costs have been estimate based on previous projects with some risk added. Detailed design to be carried out in GD/1.

• Planting and Environmental Surveys have been estimated based on previous surveys with some risk added.


26 December 2019

• The length of construction phase has been estimated as within 1 year with costs and risk based on a previous full site rebuild on Netherhowcleugh Offtake.

• Landowner agreement costs have also been based on Netherhowcleugh Offtake • Direct Company Costs have been estimated based on a forecast of the quantity of hours required

to complete the job in combination with the hourly rates

Benefits of Option

The Lockerbie Offtake rebuild is the recommended option as this is the optimal engineering solution for addressing the risks to security of supply, site safety and the environment in a controlled manner. The entirety of the work can be carried out with the existing site still commissioned allowing for a safe changeover.

The accompanying CBA further justifies this option.

Delivery Timescales

The timescales for completing the work within GD/2 is starting in FY 21/22 with the commissioning and completion in FY 22/23.

Key Assumptions

Reasonably conservative assumptions have been carried out in the pricing of this project which are detailed within its costing sheet from which the costs have been built up.

As with all projects, tendered contractor and materials are subject to fluctuation because of market forces which can be influenced by national events (e.g. Brexit). Risk has been embedded to combat these uncertainties as far as is possible.


This option is unique as it is the only option that can realistically address the issues listed in the problem statement.

7.4 Option 4 Pre-Emptively Repair Technical Detail

The scope for this option would be for all the assets within Lockerbie Offtake to be repaired pre-emptively ahead of a failure occurring.

In terms of addressing any degradation that has occurred on the site, the method of repair would be to carry out CM/4 inspection followed by, remediation of all defects and comprehensive painting of the site.

These works would not address fundamental issues with the site including the obsolete pressure control equipment, the technically flawed orifice plate meter or the filters which have degraded from continued pressure cycling.

Basis of Costing

During the process of developing and comparing options it was not possible to produce a plan that was a ‘comprehensive repair’ of Lockerbie Offtake. This was because the obsolescence and reliability issues with the equipment on the site cannot be addressed without full replacements.

It is therefore not technically feasible to proceed with this option as a failure of this nature is unacceptable. Consequently, a comprehensive costing for this option has not been carried out.


27 December 2019

Benefits of Option

The benefits of option 4 are the fact that it does address at least a proportion of the risk on the site with a moderate capital investment. Repair spend in relation to any degradation including corrosion and coating defects could be as targeted as possible.

However, most of the issues explained in the problem statement are not addressable through repair. The risks are explained in the ‘consequence of failure’ section.

Delivery Timescales

A repair on all issues on Lockerbie Offtake that can be addressed would take approximately 12 months.

Key Assumptions

When considering this option, it is assumed that the repair work would be undertaken under the normal CM/4 process, mostly carried out by direct labour.


This the option that came the closest to being credible and at least addresses a proportion of the risk. However, due to some shortcomings it has been dismissed.

7.5 Options Technical Summary Table

Table 13: Options Technical Summary Option First Year of Spend Final Year of

Spend Volume of

Interventions Equipment / Investment Design Life

Total Cost

Replace on Failure Year of Failure (Projected < 5 Years)

Year of Failure + 1 Year

As Required

< 5 Years Not Technically Feasible

Repair on Failure Year of Failure (Projected < 5 Years)

Dependent on Repair Requirement

As Required


Pre-Emptively Replace

FY 21/22 FY 22/23 Lockerbie Offtake (4)

40 Years + £1.736m

Pre-Emptively Repair

FY 21/22 FY 22/23 Lockerbie Offtake (4)



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7.6 Options Cost Summary Table Table 14: Cost Summary

Option Cost Breakdown Total Cost (£m)

Option 1 Replace on Failure n/a Not Technically Feasible

Option 2 Repair on Failure n/a Not Technically Feasible

Option 3 Pre-Emptively Replace See Table 15 Below £1.736m

Option 4 Pre-Emptively Repair n/a Not Technically Feasible

Table 15: Option 3 Detailed Cost Summary Item Note % of Total Installed

Net Cost

Total installed costs of £1.736m have been derived by combining directly estimated costs with allowance for efficiencies, overheads and other project specific factors.

8 Business Case Outline and Discussion The process of determining the preferred option for addressing the integrity issues on Lockerbie Offtake has required an assessment of several options. A comparison of the technical issues as well as the required capital investments and CBAs have enabled alternative options to be eliminated. A thorough assessment of these considerations has allowed for a robust business case for the preferred option.



29 December 2019

8.1 Key Business Case Drivers Description

Table 16: Summary of Key Value Drivers Option No. Desc. of Option Key Value Drivers 1 Replace on Failure Defers Capital Investment until a failure event lowering

immediate expenditure. Faulty component(s) would be replaced as new lowering risk following the event. However, the consequences of failure are not such that can be tolerated this option is discarded

2 Repair on Failure Defers Capital Investment until a failure event lowering immediate expenditure. Faulty apparatus would be repaired dependent if it is possible (depends on failure mode). However. the consequences of failure are not such that can be tolerated this option is discarded.

3 Pre-Emptively Replace This option has the highest risk reduction and allows for the works to be conducted in a planned way. Proactive intervention demonstrates a commitment to maintaining a safe network for the customers of Dumfries and Galloway.

4 Pre-Emptively Repair Lower Capital Investment as interventions are targeted on problem areas. However, this investment will not address a large proportion of the risk on Lockerbie Offtake. This option is not a technical solution and is therefore discarded.

The below table summarises the Cost Benefit Analysis Results for carrying out the Full Site Rebuild at Lockerbie Offtake. As a means of comparison “Repair on Failure” has been assessed as a baseline option (bare minimum) which includes ongoing maintenance and repair costs.

Table 17: Summary of CBA Results

NPVs based on Payback Periods (absolute, £m)

Option No. Desc. of Option

Preferred Option (Y/N)

Total Forecast Expendi

ture (£m)

Total NPV 2030 2035 2040 2050

Baseline (2) Repair on failure N -0.44 -17.75 -1.18 -2.23 -3.82 -8.34

3 Pre-Emptively Replace Absolute NPV Y -2.18 -3.84 -1.82 -2.25 -2.62 -3.19

3 Pre-Emptively Replace Absolute NPV Y -2.18 -3.84 -0.65 -0.03 1.19 5.16


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NPV vs Years for CBA Comparison for Lockerbie Offtake

The option for a full site rebuild at Lockerbie Offtake gives an expected positive NPV by FY 35/36.

8.2 Business Case Summary A failure on Lockerbie Offtake is a High Impact Low Probability event (HILP) which is projected to increase in probability over GD/2 without intervention. The cost associated with a lot of supply as associated with Lockerbie Offtake is high because it is a single source supply to more than 32,000 customers. No changes are expected of the site’s strategic importance and therefore the projected NPV of £8.37m by FY 56/57 for the preferred intervention, to rebuild Lockerbie Offtake.

This increase in risk is modelled by Monetised Risk Software and is considered as a part of robust calculations in the accompanying CBA. Several options to resolve this have been investigated but most have proved to not be viable.

Table 18: Business Case Matrix (Rounded to 2 decimal places)

Option 3 Pre-

Emptively Replace

GD2 Capex (£m) 1.74 Number of Interventions 0.00 Carbon Savings ktCO2e (GD2) 1412.99 Carbon Savings ktCO2e /yr 282.60 Carbon Emission Savings (35yr PV, £m) 1.72 Other Environmental Savings (35yr PV, £m) 0.00 Safety Benefits (35yr PV, £m) 8.22 Other Benefits (35yr PV, £m) 0.10 Direct Costs (35yr PV, £m) -1.67 NPV (35yr PV, £m) 8.37 High Carbon Scenario

Carbon Emission Savings (35yr PV, £m) 2.58

(20.00)

(18.00)

(16.00)

(14.00)

(12.00)

(10.00)

(8.00)

(6.00)

(4.00)

(2.00)

-0 10 20 30 40 50 60

Net

Pre

sent

Val

ue (£

m)

Years

Lockerbie Offtake

Baseline Option 1


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High Carbon NPV (35yr PV, £m) 9.23

9 Preferred Option Scope and Project Plan 9.1 Preferred option The preferred option is to deliver the full site rebuild of Lockerbie Offtake in RIIO GD/2. The capital investment for this option is a total installed cost of £1.736m.

9.2 Asset Health Spend Profile

Table 19: Spend Profile Overview Asset Health Spend Profile (£m)

Pre GD2 2021/22 2022/23 2023/24 2024/25 2025/26 Post GD2

1.150 1.343 0.393 0.00 0.00 0.00 0.00

9.3 Investment Risk Discussion Some Investment Risks exist that could be hurdles to the Lockerbie Offtake full site rebuild being delivered within the defined timescales and budget.

As previously mentioned, SGN does not have direct control over market forces that can cause contractor and material costs to fluctuate (these can be influenced by national events including Brexit). For this project, a large proportion of this risk is mitigated as the procurement of the long lead time costly materials has occurred in GD/1. Consequently, this removes a line of expenditure that could otherwise be subject to fluctuation.

A reasonable allowance for uncertainty has also been included to mitigate against the remainder of this risk.

Other full site rebuilds could be subject to risks associated with building a new site on newly purchased land. This includes financial risks in the certainty of the price of land as well as unknown ground conditions. For Lockerbie Offtake, these risks have been mitigated by opting to build the new site within the existing compound as there is ample space available.

This does however, present additional risks associated with carrying out construction in proximity to operational plant. A safety orientated design around construction phasing and adherence to safe working procedures like SW/2 are used to mitigate these risks.

Sensitivities have been applied to the Transmission Integrity CBAs as follows:

• Variations in Capex project cost have been applied for the range -10% to +20%. These are considered realistic ranges based on our experience in GD1 and the likely pressures on cost in relation to the procurement of materials and main contracts.

• Variations in methane levels (and therefore environmental impact) have been considered to take account of the anticipated introduction of hydrogen. SGN have committed to a ‘net zero’ carbon network by 2045. In practice that means no methane by that date. Also, while the use of hydrogen in distribution is being actively investigated and hydrogen is currently being introduced into a network for the first time since the conversion to natural gas, it is considered very unlikely that hydrogen will be injected on a wider scale until RIIO-GD3. For


32 December 2019

these reasons, methane levels have been considered in three ranges: aggressive early transition, mid-case and late transition.

Methane / hydrogen transition – sensitivities

The current version of the CBA template, version 4, already acknowledges that methane is estimated to be 28 times more damaging than CO2. This figure is taken from the IPCC Fifth Assessment Report published in 2014. Since this figure is derived from the latest science, it is not considered prudent to test for sensitivity in this area.

Sensitivity in the value / cost of carbon is already included within the CBA template with base-case and high-case scenarios mapped out. These sensitivities are considered sufficient in our CBA.

Table 20: Sensitivity Analysis for the preferred option 3, Full Site Rebuild of Lockerbie Offtake (rounded to 2 decimal places)

Low Mid High GD2 Capex (£m) 1.56 1.74 2.08 Number of Interventions 1 1 1 Carbon Savings ktCO2e (GD2) 1,413 1,413 1,413 Carbon Savings ktCO2e /yr 283 283 283 Carbon Emission Savings (35yr PV, £m) 1.7 1.7 1.7 Other Environmental Savings (35yr PV, £m) 0 0 0 Safety Benefits (35yr PV, £m) 8.2 8.2 8.2 Other Benefits (35yr PV, £m) 0.1 0.1 0.1 Direct Costs (35yr PV, £m) -1.5 -1.7 -2.0 NPV (35yr PV, £m) 8.5 8.4 8.0

Project payback has not been carried out as part of this analysis due to the effect of the Spackman approach. For a cash-flow traditional project payback period please see scenario 4 of our Capitalisation Sensitivity table

Consumers fund our Totex in two ways – opex is charged immediately though bills (fast money – no capitalisation) and capex / repex is funded by bills over 45 years (slow money – 100% capitalisation). The amount deferred over 45 years represents the capitalisation rate. Traditionally in ‘project’ CBA’s the cashflows are shown as they are incurred (with the investment up front which essentially is a zero capitalisation rate). Therefore, we have developed scenarios that reflect both ways of looking at the investment – from a consumer and a ‘project’.


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The scenarios are summarised as follows: • Scenario 1 - we have used the blended average of 65%, used in previous iterations of this

analysis. • Scenario 2 - we have represented the Capex and Opex blend for the two networks, as per

guidance. • Scenario 3 - addresses our concerns on capitalisation rates whereby Repex and Capex spend

is deferred (100% capitalisation rate) and Opex is paid for upfront (0% capitalisation rate). • Scenario 4 - this reflects the payback period in ‘project’ / cash-flow terms and provides a

project payback. We have taken a view of the NPV in each of the scenarios, with the exception of scenario 4, at the 20, 35 and 45 Year points, to demonstrate the effect of Capitalisation Rate on this value.

Table 21: Capitalisation Rate Variation (rounded to 2 decimal places) Scenario 1 2 SC 3 4 Capex (%) 65 46 100 0 Opex (%) 65 46 0 0 Repex (%) 100 100 100 0 Output NPV (20yr PV, £m) 1.59 1.54 1.69 NPV (35yr PV, £m) 8.37 8.37 8.37 NPV (45yr PV, £m) 13.87 13.89 13.84 Payback 13.00 14.00 10.00 15.00


34 December 2019

Appendix A – Acronyms

Acronym Backronym (spelled out acronym) Definition / explanation

A1, A2, B and C Grading System following PSSR inspections

A1 is Imminent Danger, A2 is a Significant Fault, B is a non-significant fault and C is no fault

BEIS Business, Energy and Industry Strategy

The Department of Business, Energy and Industry Strategy overseeing expenditure and administration of GD2

Software application used to model SGN's calculations consistent with the NARMs methodology. The application is highly aligned with ISO 55000, the international standard for Asset Management.

CBA Cost Benefit Analysis Analysis carried out to quantify the financial benefit of carrying out a particular intervention considering the capital investment necessary.

CM/4 SGN Procedure for Condition Monitoring SGN Procedure for Condition Monitoring

DG District Governor

A Pressure Reduction Installation - Equipment used to reduce pressure across different pressures and in this case where the supply is to a low-pressure network

DP Differential Pressure

Used to describe the difference in pressure between two sides of an interface, e.g. the inlet and outlet of a filter or the inlet and outlet of a regulator

DPG Distribution Pressure Governor

A Pressure Reduction Installation - Equipment used to reduce pressure across different pressures where in this case the supply is to a medium pressure network

E&I Electrical and Instrumentation

Discipline of engineering concerned with Electrical Assets and Instruments used on gas installations

GD/2 Gas Distribution 2 The next price control that Ofgem will set for the gas distribution networks. Due to begin FY 21/22.

GDN Gas Distribution Network

Gas Distribution Network Geographical Supply Area’s

Governor Pressure reduction installation

Equipment used to reduce pressure across different pressures

GRP Glass Reinforced Plastic

Current Industry Practice is to enclose PRIs within GRP kiosks. These incorporate, appropriate ventilation, explosion relief, weather protection for equipment and associated instrumentation, noise attenuation and improved security and safety for site personnel.



35 December 2019

HDPE High Density Polyethylene

A High Density Thermoplastic Polymer used for distribution pipelines particularly higher pressures like IP

HI Industry Health Rating Health Indices

HILP, HIHP High Impact Low Probability and High Impact High Probability

Acronyms which give a condensed description of the risk level by stating whether the likelihoods and consequences are high or low.

HP, IP, MP & LP Pressure Regimes

Industry acronym for pressure tiers, High Pressure (Above 7 barg), Intermediate Pressure (Above 2 barg to 7 barg), Medium Pressure (Above 75 mbarg to 2 barg) and Low Pressure (Below 75 mbarg)

HSE Health & Safety Executive

Government agency responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare

HSWA Health and Safety at Work The Health and Safety at Work etc Act 1974

IDN/PM/P/11

Inspection, assessment and repair of damaged (non-leaking) steel pipelines greater than 150mm nominal diameter, designed to operate at pressures greater than 2 barg

Procedure which dictates the process of dealing with defects on pipelines to resolution. This process can only be undertaken by competent assessors.

IGEM/GM/8 Industry Standard for Meter Installations Meter installations of flow exceeding 6 m3 per hour

IGEM/SR/25 Industry Standard for Hazardous Area Classification

Hazardous Area Classification of Natural Gas installations

IGEM/TD/13 Industry Standard for Governor Replacement Industry Standard for Governor Replacement

IGT Independent Gas Transporters

Independent Gas Transporters (IGTs) develop, operate and maintain local gas transportation networks. IGT networks are directly connected to the Gas Distribution Network (GDN) via a Connected System Entry Point or indirectly to the GDN via another IGT. Although domestic, industrial and commercial premises are connected to IGT networks, new housing and commercial developments form the largest share of the IGT market. It is estimated that the number of consumers connected to IGT networks is around one million.

LGT Local Gas Treatment

The process of putting additives into natural gas for a defined purpose. In the context of transmission stations, the only treatment carried out is the injection of odorant.


36 December 2019

LTS Local Transmission System

Term used to describe the high pressure pipelines which are owned by SGN. The gas within these pipelines is odourised as they transmit gas between the Offtakes and PRSs.

MOP Maximum Operating Pressure

The maximum pressure that an asset is permitted to run at continuously

MPI Magnetic Particle Inspection

Non-destructive testing method of detecting surface and shallow subsurface discontinuities in ferromagnetic materials by putting a magnetic field into the part and using ferrous particles.

MWC Main Works Contractor Contractor responsible for the overall delivery of a major project. They will usually use other sub-contractors for aspects of the job.

NARMs Network Asset Risk Measures

The agreed methodology through which base data on asset health in combination with the consequences and financial cost of failure is used to calculate the monetised risk on assets. This allows the financial impacts of interventions on assets to be quantified and benchmarked.

NDT Non Destructive Testing

Methods of testing typically the structural strength of an asset without destroying it (it can therefore still be put in service). Examples of this would be hydrostatic testing and MPI.

NTS National Transmission System

Term used to describe the high pressure pipelines which are owned by National Grid. The gas within these pipelines is not odourised as they transmit gas between the various sources and the Offtakes.

PE Polyethylene Thermoplastic Polymer used to construct plastic distribution pipes

PIA Post Investment Appraisal

Method used to evaluate the impact of investments made by SGN

PRE Gas Escape Public Reported Escape

PRE Public Reported Escapes

Gas escapes reported by the general public through the gas emergency number 0800 111 999

PRI Pressure Reduction Installation

Equipment used to reduce pressure across different pressures

PRS Pressure Regulating Station

Term used to describe the stations which regulating high pressure gas down to a lower pressure

PRU Pressure Regulating Unit

Another term used to describe a pressure regulating skid that can be purchased as a package

PSR Pipeline Safety Regulation Pipeline Safety Regulation 1996

PSSR Pressure System Safety Regulations Pressure System Safety Regulations 2000

RIIO Revenue Incentives Innovation Outputs Ofgem Price Control

RRP Regulator Reporting Pack

Ofgem annual workload and finance reporting mechanism


37 December 2019

scmh Standard Cubic Metres per Hour

A standard cubic metre of natural gas is the quantity within 1 cubic metre at 15 degrees Celsius and 101.325 kPa. It is essentially the equivalent of a mass flow rate of natural gas.

SEPA Scottish Environmental Protection Agency Scotland's Principle Environmental Regulator

SGN Scotia Gas Networks Scotia Gas Networks company name

SGN/PM/FAULT/1 SGN Management Procedure for The Reporting of Faults

Management Procedure for The Reporting of Faults on Gas Transmission, Distribution and Gas Supply Metering Assets

SGN/PM/PS/3

Management Procedure for Ensuring Compliance with The Pressure Systems Safety Regulations 2000 for Gas Pressure Systems. General Compliance Duties

SGN's management procedure to comply with the applicable regulations of PSSR 2000.

SGN/WI/PLANT/1 Work Instruction for the Delivery of Plant Projects

This instruction provides guidance on the key stages of a PS/6 project (Parts A to F) and includes a step-by-step process for the commissioning, site handover and records capture requirements for above 2bar PS/6 projects on maintained assets.

SGN/WI/SW/2

Work Instruction for Safe Working in the Vicinity of Pipelines & Associated Installations with maximum operating pressure > 7 barg

Instruction for all persons involved with works carried out in the vicinity of SGN's high pressure pipelines and associated installations with maximum operating pressures > 7barg.

SOL Safe Operating Limit The safe operating limit is the operating limit (including a margin of safety) beyond which system failure is liable to occur.

SPRS Small Pressure Regulating Station

Pressure Regulating Station which typically supplies only a small town or village. Consequently, the pipework is of a small diameter and all assets can be incorporated into a single skid.

USM Ultrasonic Meter Meter used to measure the velocity of natural gas and therefore the volume flow rate through the site

VS02 Industry Standard for Visual Inspection

Visual inspection of gas network equipment as required by the Pressure System Safety Regulations and the Pipeline Safety Regulations.

Engineering Justification Paper Lockerbie Offtake Full Site … · 2020-01-06 · pipeline from Lockerbie instead it only supplies downstream PRSs. There are more than 32,000 customers

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