Network Maintenance

SNGPL uses CBM techniques for effective asset management

Asset management is the process of maintaining, upgrading and operating physical assets in a cost-effective manner. It has been made even more imperative by the increase in energy demand. The valuable and cost-effective realisation of assets needs to be undertaken in a way that provides organisations with management capabilities for meeting the desired level of asset reliability at the lowest possible ownership cost.

Sui Northern Gas Pipelines Limited (SNGPL) is a core distribution and transmission company in Pakistan. It has been managing a 94,263 km long gas pipeline network that covers the northern part of the country. SNGPL uses condition-based maintenance (CBM) techniques with a geographic information system (GIS) for managing assets in its gas distribution network.

Need for GIS

GIS has emerged as a powerful technology that supports enterprise management and presents a spatially correct and graphical representation of gas pipeline networks, linked to associated databases of assets, attributes and customers. It allows users to integrate data and methods in ways that support traditional forms of geographical analysis, such as map overlay analysis. In other words, GIS helps maintain asset knowledge and enables better use of capacity in terms of the pressure and inlet quantity of gas. It enables the use of existing pipeline infrastructure before embarking on expensive new builds.

Asset management techniques

Different management techniques, such as corrective maintenance, time-based maintenance, reliability-centred maintenance (RCM) and CBM, can be followed.

Study area

Shahdara is a northern suburb in Lahore, Pakistan. As of June 2015, it had a population of 600,000, 4.8 per cent of the city’s total population. It mostly has industries like moulding, steel, textile manufacturing and thermal power plants, which depend on natural gas.

Data collection

The first step is to collect data for preparing the spatial database, with the major requirements being distribution layout drawings and attribute data. The distribution pipeline network is managed manually by handmade layout drawings, which contain pipeline network information on town border stations (TBSs), sales meter stations, cathodic protection (CP) stations, reducers and valves. Manual asset records contain information related to pipelines (diameter, length, electric current in ampere, wall thickness), TBSs (size, type, wild growth, fence, regulators, condition of floor, painting remarks), CP (AC-DC voltage converter and regulator condition) stations, valves (size, painting, maintenance date, cracking lubrication) and reducers (type, size).

The working method comprises three phases. In the first phase, a requirement analysis is carried out to determine spatial and attribute data needs. The information is gathered and digitised with the spatial information system, and the attribute data is then prepared in spreadsheets and integrated with the spatial data. In the second phase, the input data is analysed and transformed to the respective layers. The following GIS layers are prepared through the GIS software: sales meter station layer; pipeline layer; TBS layer; valve layer; reducer layer; and CP station, using ArcGIS 9.3. In the third and final phase, the output of the second phase is examined and the necessary suggestions are made.

Methodological framework of CBM approach

Conventional handmade maps and manually handled asset record books of the study area, which are acquired as preliminary datasets, are geo-referenced. On the basis of this information, TBSs, valve locations, reducer locations and CP sites are identified and stored in the geo-database. Global positioning system-based surveys are then conducted for the ground validation of assets, after which the geo-database is used for accurate network and asset analysis. Asset condition reports are generated spatially to analyse asset conditions and maintenance requirements using ground-validated datasets of the study area. Finally, the geo-database is deployed in SNGPL and updated approximately twice a week for accurate and uninterrupted information about asset conditions.

Results and analysis

SNGPL uses CBM as an effective tool for managing assets. The continuous monitoring and updating of asset data reveal where assets are located and which of them require maintenance or are in critical condition. This helps save time and reduces site visits.

Gas pipeline analysis: Gas pipeline analysis involves making a pipeline summary according to diameter, classification, type and the total gas pipelines in the study area. As of June 2015, the total pipeline length in Shahdara was 420 km, and 7.1 per cent of the total gas pipeline is polyethylene (plastic).

TBS analysis: A TBS reduces gas pressure from the main supply pipeline to distribution lines. It consists of a regulator, valves, pressure gauge, fence and reinforced cement concrete slab. Proper painting and cleaning is required to prevent pipelines from erosion and environmental effects. As of June 2015, the Shahdara gas distribution network had 12 TBSs. Seven TBSs were found with missing pressure gauge, five with poor painting and four with no fence. It was also observed that eight TBSs needed proper cleaning to remove wild growth.

Valve analysis: Valve functions include the on/off service, throttling service (flow control), prevention of reverse flow (backflow), pressure control, regulation, and pressure relief. Effective valve maintenance can be accomplished using cleaners and introducing proper lubricants at regular and frequent intervals. As of June 2015, the total valves in Shahdara’s pipeline gas distribution network was 174. Of these, 21.26 per cent valves were found with poor lubrication, 42.52 per cent with poor painting, 4.02 per cent with broken slabs and 2.29 per cent with missing pit covers. The analysis further showed that three valves were in critical condition with poor painting, poor lubrication as well as broken slabs.

CP station analysis: The CP station is used to protect buried iron and steel pipelines from corrosion by preventing the anodic reaction of metal dissolution on the structure under protection. Sacrificial anode CP and impressed current CP techniques are used in the field, with SNGPL making extensive use of the latter. A total of three CP stations were found in Shahdara’s pipeline network as of June 2015. One station (installed on a 6-inch main supply pipeline) was found to need proper cleaning while two CP stations (installed on a 4-inch and 12-inch pipeline respectively) required proper painting.

Conclusion

This study applies the CBM model to asset management in SNGPL’s gas distribution pipeline network. The use of GIS in a gas distribution network provides spatial distribution, while CBM provides information about asset condition. The integration of CBM and GIS provides an advantage over manual and conventional systems. CBM further enables the updating and modifying of assets and identifying appropriate locations for installing new assets through GIS maps. The system can be further improved by implementing RCM for real-time monitoring of assets and multiple monitoring factors; however, this entails a higher cost.

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