Orhan Degermenci
Author: Orhan Degermenci
Dr. Orhan Degermenci (BSc., M.E. and PhD in Petroleum Engineering from the Technical Univeristy of Clausthal in Germany) with his full-time of 28+ years job experience is involved as both lead and specialist engineer in engineering design (FEED & DD & EPC & PMC and O&M Projects) of numerous oil+gas+water+refinery product piping & pipelines.
Other Articles by Author

It is assumed that at commencement of the planning works the start and end points as well as the approximate line pipe diameter have been fixed up. The pipeline is the essential part dominating the construction costs, but there is not the only one component of the transportation system.

Therefore, during the planning and routing the possible interference with other system components (particularly with the stations) shall be considered. The information on necessary site requirement for the construction (working stripe width) and on the geometry at direction changes (bending radius) which are required for the routing works will be derived from the line pipe diameter. The connection line between the starting point, enforced points prescribed by the system as well as the end point of the pipeline defines the ideal line of the route (Fig. 2.2-1).

Crude Oil Pipeline Route

Selection of Rough Pipeline Route

The fixing of the rough pipeline route is an optimization task, whereas beside the technical and economical, also other aspects have to be taken into consideration. These “other” aspects are defined in Europe mostly in context with regional planning and the environmental protection. It is quite imaginable that also strategically or politically reasons can have influence on the route selection.

The following steps are recommended:

  1. The thinkable possibilities for the route alignment will be incorporated in an overview map. On this occasion it is to check for first time whether in wider route corridor other pipelines, high voltage lines or traffic roads are running, which are suitable for a parallel arrangement. This thought of “route bundling” is already realized in many cases and can perform a real contribution for landscape protection in case of a reasonable application (forest aisle) and will normally be advocated by the public authorities.
  2. Flying over and travelling along the “map route”. First advance selection. Procurement of maps in smaller scale (1: 25,000 to 1: 50,000), of geological documents and aerial views. Preparation of preliminary profile for hydraulic calculations.
  3. Visiting of the key locations and enforced points in the nature. First authority contacts. Survey of the protection areas, regional planning concepts, other projects and possible right of way problems.
  4. Fixing, analysis and comparison of the route alternatives which are available for the narrowing selection.

This methodology is related to the large pipeline projects. For smaller projects (short pipeline with many clear defined enforced points) different steps can be avoided. In the practice the exact compliance with the recommended sequence is mostly not possible, and chronological parallel working out of the planning steps are necessary.

The technical-economical comparison shall comprise to some extent the following steps:

  • Assessment of the technical quality of route under particular consideration of safety for the pipeline.
  • Analysis of the construction costs under particular consideration of topography, conditions of soil, accessibility of the route during construction implementation and the necessary special points (crossings, tunnels, etc.).
  • Analysis of the impacts on the operation costs under particular consideration of energy costs (elevation profile, pipeline length) and maintenance cost (route accessibility, maintenance intensive sections, authority instructions).
  • Assessment of the expected authority instructions and the possible difficulties for acquisition of the right of way inclusive of the estimation of combined costs and delays.

The technical-economical comparison has the target to reduce further the number of alternatives or, wherever it is possible to propose one of the alternatives as being the most favorable solution.

Upon availability of the results the investigation of the selected route(s) will be deepened both in field works (commencement of the detailed routing) as well as throughout the further negotiations with the regional and supra-regional authorities, until sufficient basics are existing for the final decision.

The selected route will be illustrated in an overview map and in the route maps (1: 25,000 to 1: 50,000). The overview map shows the location of the individual route maps beside of political structure of the planning area. For the elevation profile the scales will be chosen in such a manner that both the terrain as well as line hydraulic can be visualized clear and expressively.

Detailed Pipeline Routing

In order to be able carrying out the detailed routing efficiently and to reduce extensively the risk of rerouting, the following preconditions must be fulfilled at the commencement of this work:

  • The roughly route is coordinated with all responsible authorities and with all pressure groups or lobbies who are participating in the approval procedure.
  • In area of key locations (where there are no or technically very costly alternatives existing) the negotiations with the responsible bodies let recognize that the right of ways can be acquired on a basis of acceptable conditions.

First, the enforced points which are derived from the roughly route will be visited in the nature using route maps and aerial photographs, and the possible connecting lines will be studied in detail through uninterrupted walking.

The aspects as described for the roughly routing are valid also for the detailed routing:

  • The route must make possible the laying of the pipeline.
  • The connection between the enforced points of the roughly route shall be traversing linear as much as possible.
  • Simultaneously, it is aimed to keep the construction costs as lowest as possible.

 It is of decisive importance to have the correct selection of the crossing locations with water runs and traffic roads taking into account the requirements of authorities. This optimization task requires the use of an expert, who has enough routing experience and knows the technology and cost structure of the pipeline construction.

The thought of route bundling and parallel alignment which has been described in frame of the roughly route selection is to be taken into account also in context with the detailed routing.

The detailed route as it is defined will be marked in the nature by using of the angle-point picket. The position of the angle-points will be fixed up through preparation of survey sketches and through preliminary incorporation in the agricultural land register or general parcelling maps.

Route Surveys and Route Maps

It is the task of this activity to create reliable and definitive documents for the approval procedure, the acquisition of the right of way and the construction of the pipeline.

Land Surveys

Due to missing accuracy the existing agricultural land maps and land register maps as being surveytechnical reference system are not suitable for the detailed routing in most cases. Therefore, the thought has prevailed nowadays extensively that for the total survey a structure must be created which is rigid and independent from the agricultural land maps. For that purpose a traverse will be surveyed almost parallel to the pipe axis in sufficient distance (so that the points can not be affected adversely anymore by the construction activity) and connected with the public coordination network. As reference system for the elevation profile the existing elevation fix points are used. The angle points and the axis of the pipeline must be surveyed indeed additionally with regards to recognizable land borders in order to fit the route alignment into the land maps with highest possible accuracy. In course of both the detailed routing and land survey, all factors which are essential for the detailed planning, approval procedure, right of way acquisition and construction of the pipeline have to be identified and surveyed on the traverse. The objects belonging to these factors are such as waterways and rivers, fishponds, water sources or springs, water wells, traffic areas, above and underground foreign plants and agricultural areas (farm lands, meadows, forests). For the special points (crossings) which require a detailed planning or for which a particular approval procedure is requested, a detailed land survey has to be carried out. Such cases refer mostly to the construction of crossings within the areas of major waterways or rivers.

Route Maps

Normally, the following design engineering documents shall be prepared for planning of pipelines:

(A) OVERVIEW ROUTE MAPS in scale of 1: 25,000 (or 1: 50,000) with the following contents:

  • Map section,
  • Route, stations and line block valves,
  • Key plan of plot plans,
  • Essential crossings,
  • Information on geology and soil characteristics, and
  • Political structure in route section (states, municipalities, districts, communities).

(B) OVERVIEW LONGITUDINAL PROFILE with the same longitudinal scale like the overview route maps and corresponding excessive increase.

(C) PLOT PLANS: The route will normally be fitting into the corresponding agricultural land map section (scale 1: 1,000; 1: 2,000; 1: 2,500 or 1: 2,880), whereas the result of all surveys will be supplemented. The plot plan shall contain all information which is essential for construction of the pipeline such as:

  • Survey data (angle points, distances, kilometer points);
  • Pipe diameter, wall thickness, pipe material, coating;
  • Indication on detailed plans and typical drawings;
  • Special construction measures (water depths, buoyancy protection), and
  • Information regarding cathodic protection as well as marker posts.

(D) RIGHT OF WAY DRAWINGS: These drawings will be prepared in the same scale and with the same sheet arrangement like the technical plot plans. They shall contain only such information which is necessary for the right of way acquisition and create the context with the registers. The right of way strip and contruction strip will be incorporated in land register maps in addition to the route, whereas not only the intersection points of tangents but also the alignment of the bended pipe string is to be considered at direction changes of the large pipelines.

(E) LONGITUDINAL PROFILE: Generally, the drawing of longitudinal profiles in scale of technical plot plans can be avoided during the planing phase, if the survey result is presentable in the overview longitudinal profiles having the quality and accuracy suitable for hydraulic design calculation and wall thickness definition. The detailed longitudinal profile shall be produced in the course of as-built documentation (inventory control) and contain beside ground level elevation also the pipe top level, all internals as well as weld numbers (correlation possibility with the pipe book).

(F) DETAILED CONSTRUCTION DRAWINGS: For construction of water and road crossing the survey results will be outlined both in a plot plan and a longitudinal profile using pipe axis. Depending upon object size the scales of these drawings are varying between 1: 500 up to 1: 1,000. The result of pipeline design including all information necessary for pipeline construction will be incorporated in those detailed drawings as well. In order to facilitate the preparation and subsequent handling of the drawings, a particular attention shall be paid to a clear allocation of overview, plot and detailed drawings by means of both reasonable drawing numbering system (register) and sufficient remarks or references.

Registers

The drawing registers and lists are to be prepared with a clear reference to drawing documentation in order to ensure an efficient execution of the approval procedure and right of way acquisition. For that prurpose some examples are covering items such as:

  • list of landowners and beneficiaries,
  • register of the responsible authorities and the concerned corporate bodies or legal entities,
  • schedule of crossings with water bodies or rivers, roads and foreign objects including indication of responsible locations.

These registers are also valuable for construction works at a later stage (communication, special precautions, acceptance tests and inspections).

Pipeline Design

Scope

It is assumed that the following preconditions are fulfilled at the beginning of this design step:

  • Pipeline diameter is defined, line pipe material and nominal wall thickness taken into account are selected.
  • Longitudinal profile of pipeline is determined.
  • Hydraulic design calculations including pressure surge analysis are carried out so that expected operation pressures are known for the entire pipeline.
  • Safety factor to be maintained is known.

 This section is dealing thus only with design engineering of the pipe string and the related crossings.

Distribution of Line Pipe Wall Thickness

If the lines of maximum allowable operation pressure (MAOP) calculated according to the Boiler- Formula (Hoop-Stress) for different nominal pipe wall thickness are plotted into the hydraulic profile containing the gradients of the normal operation and line of maximum achievable pressure levels under unsteady or transient flow conditions, then there will be obtained such points for which a wall thickness change is necessary (Fig. 2.2-2):

pipeline wall thickness  distribution

For difficult profile it is recommendable to plot additionally the pressure line, under which the pipe will be strained up to the yield strength. By means of this line the hydrostatic pressure test can be taken into account for wall thickness distribution.

Also the selection of the minimum wall thickness needs to be verified for pipelines of large diameter. The possible cost savings through reduction of steel quantity can be absorbed again through increased construction costs, if the wall thickness falls below by ca. 1 % of pipe diameter. Below this value there is existing an increased risk of dents particularly in rocky soils. Upon determination of wall thickness values according to the Boiler-Formula the line sections at crossing locations are to be checked with regards to additional strains which might be caused by soil cover (height of above ground soil, traffic road loads, installation or clamp forces, bend output forces, etc.) and to correct at these points, if necessary.

Water Crossings

Generally, the water bodies such as rivers, streams, watercourses and lakes will be crossed below water level laying pipeline on bottom of these water bodies. Exceptions are the deeply incised canyons, channels with high heaped-up dams or similar stored cases, which make the construction of pipe bridges as being necessary.

In most cases or selection of crossing location and design of special construction points the technological aspects related to water-construction are more important than the aspects of pipeconstruction in most cases.

The water-construction related technological concepts are covering particularly the following aspects:

  • suitable position of the crossing location in longitudinal profile of the watercourse (without erosion or recess tendency),
  • stability of the river bed and bank,
  • soil property (rock, suitability for excavation works), furthermore for large crossings the underground soil investigations are necessary, and
  • hydrograph of the water course for estimation of the flood water risk and for determination of appropriate time for construction activity.

Already at stage of decision process for definition of water crossing location the construction work has to be taken into account covering the following aspects:

  • space demand for preparation and construction of water crossing (welding area and launch way), as well as
  • temporary storage of excavation material.

In case of river crossings the wall thickness of crossing pipe section within the river bed will be increased mostly. For safety against buoyancy the crossing pipe section obtains a concrete coating, which also protects the insulated pipeline on mechanical basis. The stresses during pipe laying activity caused in the pipe string of crossing section are to be taken into consideration, and the sufficient buoyancy safety has to be proven.

Road Crossings

If the circumstances allow this and the method of construction work represents the most economical solution, then the road will be slotted and the product pipe will be laid within the open trench. Should this not be posssible or not economical under subsoil conditions the product pipe (which must have in this case a mechanically resistant and robust coating, e.g. polyethylene) will be pressed beneath the road surface. In both cases (open-cut or pressing) a stress verification is required for the product pipe considering the earth and road traffic loads. For pipe laying without installation pipe the cathodic corrosion protection of the product pipe will not be damaged, and furthermore the problem known as ”protection pipe contact“ will be avoided. Should the particular circumstances or statutory regulations of the authorities as being responsible for the traffic roads be asking for use of installation pipe, steel shouldn’t be used in order to avoid the above described difficulties.

As alternative material the concrete or asbestos cement can be used. The internal diameter of installation pipe is 150 to 200 mm bigger than external diameter of the product pipe. The centering is ensured by plastic centering pieces or runners and the ends of the annulus on installation pipe ends are closed mostly by the corresponding sealing member sleeves.

Other Special Construction Points

The following examples can be listed up as being other special construction points:

  • construction measures for protection of pipeline within the sphere of watercourse’s influence with erosion or recess tendency,
  • stability assurance for laying of the pipeline in extremely side-slope location,
  • laying of pipeline in a tunnel,
  • enforced aboveground line alignment, and
  • protection and safety of the pipe and fill in of the pipe trench in extreme steeply sloping sections.

The design and planning of such special construction locations will be carried out independently and by appropriate contributions of skillfully experts. 

Cathodic Corrosion Protection Facilities

The survey of soil resistivity values required for design and planning of facilities for cathodic corrosion protection will be carried out at stage of detailed pipeline route investigations. Planning and design of these facilities and equipment are described in detailed manner within the Chapter 5.2 – “Corrosion Protection”.

The outcome of these activities (delivery points, anode fields, measurement locations) will be incorporated in the route alignment drawings.

Specifications and Typical Drawings

For the most important construction parts of the pipeline (pipes including coating, valves, fittings, flanges) there will be prepared and compiled in the documentation ”delivery conditions“ or so called “specifications” the following documents:

  • requirements for materials,
  • tests and inspections to be carried out during pipeline construction, and
  • factory acceptance test conditions.

The quantities and contents of these specifications can be reduced significantly so far as there are available relevant codes and standards on topics of those project documents. Besides of material specifications there will be prepared also the specification for pipeline construction which forms an important part of the construction agreement.

For crossings with insignificant watercourses and traffic roads as well as for other construction measures which are occurring along the pipeline route repeatedly the method of construction activity will be indicated in the so called “typical drawings” for supporting and shortening of specifications. Some examples of typicals are covering the following items as shown in the referred typical construction drawings:

  • Construction strip (Fig. 2.2-3),
  • Pipeline crossing method (Fig. 2.2-4),
  • Construction details of pipeline installation in protection pipe (Fig. 2.2-5),
  • Pipe cover (Fig. 2.2-5),
  • Pipe trench dimensions (Fig. 2.2-5),
  • Concrete pipe coating (Fig. 2.2-6),
  • Pipe bending rules (Fig. 2.2-7),
  • Ground water lowering (Fig. 2.2-8),
  • Buoyancy safety with concrete slaps or anchores (Fig. 2.2-9), and
  • Hydrostatic pressure testing (Fig. 2.2-10).

Distribution of working strip along the pipeline right of way

Pipeline Crossing by horizontal drilling and pressing method

Pipeline Crossing profiles and line alignments

Concrete coating of pipeline

Principle structure of a line pipe bending machine

Method of ground water lowering

Safety against buoyancy

Equipment to fill pipeline for hydrostatic pressure testing

Note: This article has been published on www.piping-world.com with permission from the author Dr. Orhan Degermenci.