Inspection chambers and manholes for sewer systems - Yesterday, today and tomorrow

Plastic pipe systems have more than 80 years of history. Plastic pipes have successfully managed to replace various traditional materials by providing reliable, noncorrosive, leak tight pipeline solutions. As pipes are not the only components of piping systems, logically would be to see the similar development of plastic chambers and manholes, but unfortunately the dynamics with manholes are different. Despite the major growth of plastic chamber/manhole market in the last two decades, their market share compared to concrete is proportionally much smaller than relevant share in pipes. In order to determine the reasons for such differences and discuss possible scenarios of plastic chamber/manhole development in the future, I would like to look in chamber/manhole development history, evaluate advantages and limitations of different production technologies, as well as discuss the activities that should support the future development. 

Sewer networks have always been important part of infrastructure pipe networks. 20th century has brought some major developments in sewer and storm drain systems – introduction of pipes and fittings made of thermoplastic materials, development of modern cleaning and inspection equipment. Plastic pipes have obtained substantial market share from traditional materials like concrete, clay, steel, etc. Plastic fittings became commodities in pressure pipe systems and in-house piping applications. Due to technological advances in servicing equipment during the last 30 years, plastic fittings and chambers became integral part of local/private sewer networks. Still utility companies responsible for municipal sewer and storm drainage remain skeptical about fitting, chamber and manhole use in gravity systems. The conservative approach is mainly based on the following arguments:

• “straight connection between manholes” rule,
• man entry required in all network access points for service,
• notion that solid weight of concrete manholes prevents floating,
• concrete manholes have been around for centuries,
• loss of watertightness is repairable and not so important factor

Long ago industry experts have concluded that those arguments are irrelevant or wrong and plastic chambers/manholes should be considered technically sound alternative to concrete. 

With all those preconditions in place, the market was waiting for another big gain for plastics, but change was not happening. Plastic chambers managed to gain substantial market share only in Scandinavia and limited market share in new local network development in other European countries (mainly private, seldom in municipal networks). Introduction of man entry plastic manholes in ‘90s, was greeted with little interest as concrete lobby was going strong. Today we like to refer to plastic manholes as fast growing market segment, but despite strong increase in sales from low base numbers, concrete manholes remain dominant in most of the European markets.

 discuss the limitations faced by plastic chambers/manholes. There are the following key factors that influence plastic chamber/manhole growth:

• conservative decision making, traditional thinking – human factor that prevents wide spread of alternative solutions,
• construction site proximity to production locations – local concrete business lobby,
• concrete manhole quality requirements – correlation between quality, lifetime and lifetime maintenance costs,
• required investment in production machinery and tooling – expensive entry into high quality and high efficiency manufacturing, feasible only for major multinational suppliers for whom injection molding of large size products is considered an ultimate goal,
• product characteristics due to production technology limitations – comparison of different properties of products made by high pressure injection molding, structural foam (low pressure) injection molding, rotational molding and pipe segment and prefab part welding technologies,
• limited choice of standard base inlet/outlet configurations –innovations that could provide required flexibility at low investment/production costs,
• negative product perception due to sales of low quality plastic chambers/manholes,
• quality of relevant European Norms and installation guidelines. 

As objective for my presentation, I would argue that the main reason for relatively slow development of plastic manholes worldwide is the lack of flexible, cost effective production technology that could match the “concrete offer”. I would discuss advantages and limitations of major production methods used in plastic manhole manufacturing and propose my vision of “perfect future manhole”.