public IReadOnlyList<NetworkDiagram> GetNetworkDiagrams( 
   Envelope extentOfInterest
)

using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
{
  // get all the diagrams
  IReadOnlyList<NetworkDiagram> diagrams = diagramManager.GetNetworkDiagrams();

  // get a diagram by name
  NetworkDiagram diagram = diagramManager.GetNetworkDiagram(diagrameName);

  // get diagrams by extent
  diagrams = diagramManager.GetNetworkDiagrams(extentOfInterest);

  // get diagrams from a set of utility network feature GlobalIDs
  diagrams = diagramManager.GetNetworkDiagrams(globalIDs);

  // get diagrams from a set of utility network feature GlobalIDs within an extent
  diagrams = diagramManager.GetNetworkDiagrams(extentOfInterest, globalIDs);
}

public List<NetworkDiagram> GetInconsistentDiagrams(UtilityNetwork utilityNetwork)
{
  // Get the DiagramManager from the utility network

  using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
  {
    List<NetworkDiagram> myList = new List<NetworkDiagram>();

    // Loop through the network diagrams in the diagram manager

    foreach (NetworkDiagram diagram in diagramManager.GetNetworkDiagrams())
    {
      NetworkDiagramInfo diagramInfo = diagram.GetDiagramInfo();

      // If the diagram is not a system diagram and is in an inconsistent state, add it to our list

      if (!diagramInfo.IsSystem && diagram.GetConsistencyState() != NetworkDiagramConsistencyState.DiagramIsConsistent)
      {
        myList.Add(diagram);
      }
      else
      {
        diagram.Dispose(); // If we are not returning it we need to Dispose it
      }
    }

    return myList;
  }
}