private void GetPipeSegmentSizesFromDocument(Document document)
{
    FilteredElementCollector collectorPipeType = new FilteredElementCollector(document);
    collectorPipeType.OfClass(typeof(Segment));

    IEnumerable<Segment> segments = collectorPipeType.ToElements().Cast<Segment>();
    foreach (Segment segment in segments)
    {
        StringBuilder strPipeInfo = new StringBuilder();
        strPipeInfo.AppendLine("Segment: " + segment.Name);

        strPipeInfo.AppendLine("Roughness: " + segment.Roughness);

        strPipeInfo.AppendLine("Pipe Sizes:");
        double dLengthFac = 304.8;  // used to convert stored units from ft to mm for display
        foreach (MEPSize size in segment.GetSizes())
        {
            strPipeInfo.AppendLine(string.Format("Nominal: {0:F3}, ID: {1:F3}, OD: {2:F3}",
                                        size.NominalDiameter * dLengthFac, size.InnerDiameter * dLengthFac, size.OuterDiameter * dLengthFac));
        }


        TaskDialog.Show("PipeSetting Data", strPipeInfo.ToString());
        break;
    }
}

Private Sub GetPipeSegmentSizesFromDocument(document As Document)
    Dim collectorPipeType As New FilteredElementCollector(document)
    collectorPipeType.OfClass(GetType(Segment))

    Dim segments As IEnumerable(Of Segment) = collectorPipeType.ToElements().Cast(Of Segment)()
    For Each segment As Segment In segments
        Dim strPipeInfo As New StringBuilder()
        strPipeInfo.AppendLine("Segment: " + segment.Name)

        strPipeInfo.AppendLine("Roughness: " + segment.Roughness)

        strPipeInfo.AppendLine("Pipe Sizes:")
        Dim dLengthFac As Double = 304.8
        ' used to convert stored units from ft to mm for display
        For Each size As MEPSize In segment.GetSizes()
            strPipeInfo.AppendLine(String.Format("Nominal: {0:F3}, ID: {1:F3}, OD: {2:F3}", size.NominalDiameter * dLengthFac, size.InnerDiameter * dLengthFac, size.OuterDiameter * dLengthFac))
        Next


        TaskDialog.Show("PipeSetting Data", strPipeInfo.ToString())
        Exit For
    Next
End Sub