Pipe Obvert Elevation – Implication, Calculation, and Applications

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Pipe obvert elevation is the vertical distance between the inside-top of a pipe and any datum. Moreover, the term ‘obvert’ means to turn. The obvert measurement mirrors the pipe invert, which measures the vertical distance from the inside bottom of a pipe. In this article, you will learn the implication of pipe obvert elevation, how to calculate it, and its applications in industry.

Pipe geometry showing pipe obvert and invert
Courtesy: OCPA

Implication of Pipe Obvert Elevation

In practice, professionals often refer to the pipe obvert level as the ceiling level. On the other hand, the pipe invert, is the floor level. When designing piping systems that rely on gravity flow, these elevation parameters are critical. Engineers and architects, need to ensure that flow remains positive throughout such systems. As a result, the obvert level at the outlet should always be lower than that at the inlet of a pipe. Otherwise, it leads to poor drainage, clogs, and flooding.

In addition, it is often the pipe obvert elevation that determines the slope of a pipe in draining systems. The pipe invert can also be used, as either of them serve interchangeably in most calculations. An example of its importance is in the case of street sewer connections and the basement of a house. If the sewer pipe obvert is not low enough in a residential area, then it eliminates the possibility of having a toilet in the basement of buildings in such an area.

Similarly, the pipe obvert elevation is important in force flow systems – systems that use a pump to drive flow. It is not as critical as in gravity flow applications. In any case, the pipe obvert elevation determines the amount of pressure a pump must overcome, thus, the power of the pump. Having a lower value minimizes the pumping requirement and ultimately, the cost of the piping design.

How to Calculate Pipe Obvert Elevation

Calculating a pipe obvert elevation is a basic task, depending on the application. However, the task requires care when deciding which measurements to use. For example, there are some pipe sections with male and female ends, which professionals refer to as spigot and bell ends respectively. The bell end is divergent so that the spigot can fit into it. Hence, the bell end offers the highest and lowest points in the pipe where water will run and is the recommended obvert and invert levels respectively.

Parameters used to calculate a buried pipe obvert elevation
Courtesy: Slide Player

Using the diagram of a buried pipe above, the pipe obvert elevation calculation goes as follows:

pipe obvert elevation = depth of cover + wall thickness

Application in Industry

From previous sections, it is clear that both the pipe obvert and invert elevations are important concepts. This especially holds true when dealing with fluid flow in drainages and other gravity flow applications. However, the use of pipe obvert elevation stands out when dealing with buried pipelines such as in sewer design.

Pipe Obvert Elevation in Sewer Design

The pipe obvert elevation of underground pipes indicates the working space limitation that excavation equipment has when carrying out an operation. Also, this elevation represents the depth to be reached to access a line for maintenance or other activities. As a result, the obvert elevation in sewer designs should not be too shallow in a way that exposes the pipe to damage from invasive activities. Nor shall it be too deep that it becomes a hassle to access the sewer for maintenance.

Generally, the public works or other regulatory body sets the lower and upper limits for this value. Often, these limits will vary depending on if a location is residential, commercial, or industrial. Whatever the case may be, the governing parameters for setting these limits are the safety of the sewage lines, and its accessibility.

a sewer located in the city

Furthermore, engineers locate manholes at intervals along the sewage system. One of their functions is to provide access for the measuring of the sewage pipe obvert elevation. Thus, builders can properly locate the central drainage point of a building above the sewage pipe obvert. When taking the obvert measurement, a professional should:

  • Ensure the tape measure, or an alternative device, seats on the crown of the pipe where the sewer pipe is tallest.
  • The tape measurement height should be read against the top of the road or hole.