Alessandro Soresina, David Walton
Case Studies from Around the World # 2004 Milan
AEM S.p.A. is the leading Italian company in the management of public utility services, based in Northern Italy (Milan), and operates in the sectors of electricity, gas and heat, telecommunications and other services which include both public and aesthetic lighting.
The parent company, AEM S.p.A.
have been listed on the Italian Stock Exchange since 1998.
With regard to gas distribution in Milan and the surrounding areas this is managed by Aem Gas S.p.A.
(the Gas Distribution company owned by AEM). The network supplies 860,000 customers with almost 1.2 billion cubic meters of gas each year.
In Milan the gas distribution activity started around 1870, with the first gas distribution network providing public lighting for the city. Later on the network was used to supply gas to domestic customers for cooking, water heating and so on.
This early gas (town gas) was produced from coal, and this kind of production lasted for more than one century. The conversion of the gas distribution system from town gas to natural gas took place between 1984 and 1994.
Fig.1. Structure of AEM S.p.A.
The development from this town gas system meant that the current gas distribution network is characterised by:
- Large low pressure network (working at 15x10-3 bar for town gas)
- Many large diameter mains (from 2 inch to 40 inch in diameter)
- “Traditional” mains materials (grey cast iron, ductile iron, steel)
In the 1990’s Aem Gas started a major replacement program of the gas distribution network in order to reduce maintenance costs and improve the networks efficiency and safety. Aem Gas used a variety of pipe lining technologies in order to satisfy the different external constraints connected to this activity. Apart from open trench burial different no-dig technologies have been adopted, such as:
- Slip lining with the accompanying pipeline diameter reduction.
- Close-fit relining with a minimum reduction in diameter.
- Pipe replacement without size reduction or “up-sizing” using “Pipe bursting”.
Polyethylene has been chosen for the renovation or replacement of all low pressure (LP) mains up to 315 mm in diameter. For medium pressure (MP) pipelines steel continued to be used because it was fully compatible with the existing system and the installation technology was well understood.
