Cross Country Pipelines
Steel pipelines are used all over the world for cross country transport of natural gas, crude oil, water, petrochemical and petroleum products at high pressures over long distances.
Engineering and Installation of Cross Country Pipe Lines form a special branch of piping design and engineering, as it involves many aspects and parameters which are normally faced with, in plant piping system within the boundaries of refinery or a chemical / petrochemical plant Special Techniques have to be adopted for design, laying welding / jointing, corrosion protection, testing, commissioning etc. The most common line familiar to all, is water line from reservoirs to different consumption points, like, water-main from Vaiterna / Tansa dam to city of Mumbai. Unlike water line, the hazardous chemical conveying Pipelines, involve many more stringent precautions in their design and installation. This is mainly due to fire and explosion hazards associated with the oils and chemicals.
Disadvantages of transport by Roads / Railways / Waterways: The most common modes of transport known to all include Trucks running over Roads, Railway goods train and Ships/Launches/Boats/Barges on waterways. The transport by Airway be cargo aircrafts is also another way of bulk transport. These modes of Transport have following limitations.Protection of Cross Country Pipelines
1 General Scope of Operation
a) Availability of sufficient roads, rail-tracks and port-harbor facilities to take up the traffic load.
b) Condition of the tracks.
c) Hurdles and conditions of the vehicles.
d) Maintenance and conditions of the vehicles.
e) Procedures and control involved in the Transport operation (permits / licenses / octroi / toll / RTO etc.)
f) Manpower to run and maintain the transport system.
g) Availability of fuel and power required to run the system.
h) Effect of Nature on the system like rains, storms, earthquakes, thundering, mist etc.
i) Pollution generated by the transporting vehicles.
k) Safety, insurance and security of the transported goods and materials.
l) Time taken for transportation and delays.
m) Overall efficiency of the system.
The modes of Transport by pipe lines have advantages, which are given below :
a) Continuous un-interrupted transport is ensured.
b) No dependence on availability of roads, railways, bridges etc.
c) Least manpower requirement to operate the transport system except for inspection and maintenance of minimum required level.
d) No hindrances on way as for surface transport, air water ways.
e) Possibility of crossing any odd areas like seas, oceans, rivers, mountains and underground space.
f) Safety & purity of the product is ensured. The product reaches exactly in the same condition from source to the supply point, with minimal loss of quality or quantity.
g) Once laid down, the system works automatically especially with the help of modern instrumentation, safety devices, interlocks, communication system and remote control devices.
h) Minimum or no tampering on the way.
h) Cost of Transport per Unit of the product conveyed is far less than the transport by
Trucks/railways/ water/ Airways.
j) Fastest mode of transport even between two countries or continents.
k) Comparatively much less hazardous than surface transport & minimum dependence on human factors.
There are of course certain disadvantages but they are offset by the advantages, to a large extent, so as to make them ignorable as far as safety & techno-economic aspects are concerned. They are listed as given below:
a) Right of way: Acquisition to run the pipeline, especially through private & agricultural land & habituated areas.
b) High fire & explosion Hazards potential.
c) Problem of corrosion & leakages & repair work involved.
d) Daily on-route inspection, testing & quick arrangements for attending to repairs and rectification work.
e) Possibility of laying other services in future (like other pipe lines due to ignorance of its existence, among other agencies) causing damage.
f) Special Techniques & Agencies are required to design, engineer, install & operate the pipe line system.
g) Expensive cathodic protection required for the protection of under gtound lines running in close proximity of overhead High Tension electrical Transmission lines which induce the currents in the metallic pipe lines, causing the corrosion by stray currents.
The modern techniques are well developed to offset the effects of the above disadvantages. Even if a line has to be shut-off for a day or two, the storage facilities at the users end take care of such stoppages even for 15 days to 1 month.
Preliminary work for A Cross Country Pipe Line Project:
The following necessary work on planning & collection of information/data is required to be done for pre-project activities, once it is decided to install a Cross Country Pipe Line.
Data on the Product to be carried:
- Name, Qty/day, properties of the product.
- Source of supply & location details.
- Names & location of consumers.
- Qty/day to be supplied to each consumer.
- Storage facilities at suppliers’ end & consumers’ end.
- Pumping facilities at Suppliers’ end.
- Unloading facilities at receivers’ end.
- Safety requirements for the product.
- Risk & Hazards associated with product.
- Interruptions in supply at suppliers’ end & at receiving end.
Route Survey & Analysis:
There may be many alternatives for routing the pipe line from supplier to the consumer. It is necessary to study the techno-economic comparison of the alternative routes. This survey includes the following activities:
a) Spot-level survey at every 50 to 100 meters & at least over 10 m on either side of the probable route.
b) Soil Conditions in the form of bore-logs, trial pits, chemical tests on subsoil & ground water etc.
c) Alignment Map With lengths, bearings, angles etc. to know the exact route & the total length of the pipe-line.
d) Details on the route and their locations, dimensions etc sea, roads (crossing and along side the route) rivers, Nallas, pipe-lines, bridges, rail-tracks, transmission lines, underground services including cables/pipes etc, Hills and mountains, buildings, plantations, forests, agricultural land etc.
e) Cadestral Survey: The route may be passing through so many lands belonging to private owners, farmers, govt. authorities, defense wings etc. En-route information and data has to be collected for such land pieces. Such data will include:
- Type of land and the owner’s name.
- Length of the route through the land.
- Problems in acquiring Right of Way (R.O.W.)
- Authority which will permit/grant ROW.
- Survey maps for the land available from the local Land Authorities (such as collector, Tahasildar, Gram-Panchayat etc.)
- Land records regarding the title and ownership of the land.
- Approx compensation required for acquiring the R.O.W.
- Status of Habitation on the land.
- Similar information of the adjacent plots on 50 to 100 m on either side of the route.
- Plans for future installations by others on the proposed route and / or in the vicinity such as roads / rail-tracks / buildings / pipe-lines etc.
f) Availability of construction Materials, Labor & facilities: Since the pipe-line has to pass through different areas and over a long distance, it is essential to know the availability of construction Labor and Materials on the way. These are excavation labor, transport facilities, access roads, construction material like stones, aggregates, sand, cement, steel, structural, etc., workshop facilities. This information will be useful in working out project schedule and cost estimates and assessing the problems in construction.
g) Soil Resistivity Survey required for design of cathodic protection system.
Names and addresses of the statutory and public bodies required to be contacted for acquiring ROW, construction permission, blasting licenses, excavating the public facilities (Roads, rivers, rail-tracks etc.) and cathodic protection work, power supply / water supply etc.
Such authorities include the following but not limited to the listed ones.
Local land authorities – district Collector, Municipal corporation, Tahsildars etc., Owners of the respective Land.
P.W.D. authorities – Local Office
Electricity supply Agencies / bodies / Boards.
Water-supply and Public Health Dept.
Controller of Explosives and use of Hazardous chemicals.
Industrial Development corporations
Marine and Port Authorities.
Salt-commissioner and controller.
Competent Authorities for Land and ROW acquisition.
State and Central Governments for necessary permissions, licenses, clearances etc.
Import / export rules / regulations authorities.
Controller of Quarrying and Mining.
Navy / Army / Air force (Defense Authorities).
Plants for future installations.
Based on various data collected and the cost Estimates, over all project schedule has to be prepared, based on past experience, and specific problems unique to the project under consideration. This schedule should cover only broad activities to serve as a guide line for preparation of detail activity schedule.
This should generally include:
a) Preliminary Survey / Data Collection.
b) Finalizing the route.
c) Cost Estimates / budget sanctions.
d) Acquisition of R.O.W. and land.
e) Basic Engineering package.
f) Detailed Engineering work.
g) Construction work (Civil / Mechanical / Piping / Electrical, Marine crossing, river crossing etc / cathodic protection).
h) Testing / Flushing / Pigging.
j) Commissioning and Hand over.
This will establish the overall completion time for the entire project work.
Detailed Design of each system:
Civil works including trenching, sand filling, back filling, buildings, concreting, river weights, valve chambers, Test points, markers and construction infrastructure like site office, construction water, power, site godown / open yards etc.
Construction Equipment required for transport, laying, welding, erection testing etc.
Piping : Stringing / Welding / Laying / Testing pipe support system.
Cathodic protection system design, diode stations, sacrificial anodes, UPS installations, on-line test-points, insulation flanges.
Specific designs for submarine portions and river-crossings.
Designs of all crossings, pipe-bridges, supports.
Preparing Detail Design and Fabrication Drawings for all Systems.
Quantity calculation for materials and work items.
Implementation Planning and Organizing:
Selection and appointing Agencies / Contractors / Suppliers for various activities and materials.
Division of work among the staff on the project.
Progress monitoring and reporting system.
Mobilizing planning (manpower deployment planning) (Resource-planning)
Implementation work packages.
Payment to subcontractor system.
Inventory control and planning.
Safety / Security Guidelines.
Organizing Revisions / Change / alternatives / improvements in system design / drawing during the project-process.
Preparation of As-Built construction drawings and final costing.
Data-Bank for the executed project, useful for future project.
Salient Features of Construction:
Trenching: Generally Cross Country Pipe Lines are laid underground in an excavated Trench while crossing the land areas. Minimum depth of the Trench to be, while crossing the land areas. Minimum depth of the Trench should be (1 M + Pipe dia + 150 mm). 1 M is the depth of overburden i.e. back filled soil, and 150mm is the thickness of sand cushion to be laid before lowering the pipe in the trench. Width of the trench is generally minimum 1 M or as required by higher diameter Pipes. Thus width should be (Diameter Of Pipe + 0.4 M on either side) or 1
meter whichever is higher.
Pipe Preparation in Yard:
- Inspection / Testing / Stacking of Pipes / Numbering.
- Edge Preparation for welding.
- Wrapping / Coating (generally reinforced bituminous) and its testing.
- Testing /Stacking bends / elbows / Tees.
- Pipe Sleeves for road crossing.
- Valve testing / stacking / numbering.
- Other accessories like blinds / spectacle blinds, gaskets, bolts, nuts, washers etc.
- Selecting / Stacking welding machine / electrodes etc.
Stringing at Site and Welding: After trenching is ready over substantial length pipe lines made ready in the yard are transported to the site and lined up over sleepers placed across the trench for welding and lined up over sleepers placed across the trench for welding the joints. The joints are welded continuously in 2 or 3 shifts. They are subject to inspection by Dye Penetration check and Radiography. Wrapping / coating is completed over portions about the weld.
Lowering: Once a fairly long length say 100 m to 150 m is welded / Tested, then if is lowered into trench over sand bed already laid. Necessary small / big cranes, lifting tackles are used for lowering the line. Back filling with soft earth free from stones is done after lowering.
Hydro testing: A long length after lowering and before back filling is hydro tested for the test pressure which is generally 1.5 times the operation pressure or as stipulated for specific service.
Overall Total Welding: After each 100 to 150 m length is lowered, tested, then they have to be welded to form a continuous pipeline. Testing of entire line is then taken up by filling the whole or section of line with water & pressuring. Any leaks found are repaired and tested.
Pigging: For flushing and cleaning the entire length of all muck, dirt, welding rod bits etc, a pig is passed through the line, from one end, and it is pushed by water pressure. The pig travels through the pipe, scrapping the muck and pushing it forward. At intermediate points flanged joints are left to pass-out the muck. If a pig gets stuck up, its location is detected by passing an ‘ISOTOPE’ and detecting its location by external instruments which tracks the isotope as it is traveling through the pipe. The pipe line is cut, pig removed, pipe cleaned and rewelded. The pig is passed through from that point onwards to flush the remaining portion in the forward direction.
Commissioning: It is done as per the procedure laid down for the specific product to be carried through the pipeline.
Cathodic Protection: This provides the protection to the underground pipe from the corrosion by electrolytic process in subsoil water, whenever in e-m-f is induced’ in it (when pipe material is a good conductor e.g. carbon. Steel)
Additional Features about Piping:
Pipe Thickness: The thickness is calculated in accordance with the standard methods and codes for different services and duty, including due corrosion allowance.
Anchor blocks at change of direction, made of concrete should be used to counteract the effects of outward thrust due to change in direction of fluid velocity.
If more than one pipe lines are running in parallel, minimum, clearance between the adjacent pipelines should be the largest of
(a) O.D. of the larger pipe dia over insulation if any.
(b) 600 mm
(c) as stipulated for specific requirement like working spacer for excavation / repairs, restrictions due to ROW space, adjacent features like road edge, building etc.
Surge Effect: Whenever the valve at or near the receiving end is shut-off, there may be surge pressure effect on the pipeline as well as Pumps / Valves at the supply end. It is therefore necessary to decide the time period for valve closing with appropriate communication between supplier and receiver. At times it may be advisable to introduce a surge tank or vessel at both the ends. This avoids the effects of Fluid-Hammer in the system.
Piging: When a multipurpose pipeline is used for carrying different products periodically, pigging has to be done in addition to flushing and making the line ready for new fluid.
Pipe line supported on Brackets attached to a Road or Railway Bridge: When a line runs along-side a bridge, the vibrations of the bridge due to Traffic Movement, are also transmitted to the Pipe line. It is necessary to estimate the vibration levels (frequency and Amplitudes) of the bridge. Generally these data will be available with the respective authorities or designers of the bridge. We have to check and prevent the natural frequencies of the pipe line, matching with the exciting frequencies of the bridge, to avoid resonance effects. It is advisable to provide lateral spring loaded supports at random intervals, to get damping effect and random frequencies. In case of railway bridges, regular patterns of vibrations are more probable when the train is passing.
Long Expansions Loops: As the line is exposed to outside atmosphere, whenever it runs along the bridge side, thermal expansion and contraction takes place due to Temperature variations. Generally a long and wide loop is provided under the bridge structural. Behaviour of short and long arms of the Loop will depend on the deflections and the stiffness of the arms.
Due analysis should be made to calculate the stresses induced in the pipe. Also note the supporting arrangement of the pipe which has following main features.
The rollers are provided to allow free longitudinal movement of the pipe due to expansion and contraction.
Loose clamps are provided over pipe line at intervals with 25 to 30 mm gap all around, to prevent possibility of the line slipping off the supports due to long length. (Long pipe line behaves like a flexible wire and when expanded, may tend to move out from the supports.
Lateral spring supports are provided at random intervals to prevent possibility of
natural frequencies of pipe matching with Bridge frequencies.
Erection Stresses: The handling of pipes may induce local and excessive stresses in following conditions.
a) When cranes are used for lowering long lengths in position, local deformation / bending may take place.
b) When pipe is pulled along the trench or through the sleeve laid across the road.
c) When the sub-marine portion of the line is gradually lowered from water level to below the sea or river bed, it undergoes deformations at local points.
d) When long un-supported (un-back filled Trenches) lengths are hydro tested, the flexibility of long lengths, sometimes causes vibrating movements on micro-scale and are more predominant than in case of small in-plant piping. These have to be correctly assessed or damped by intermediate Temporary and / or permanent supports, thrust blocks, anchors, backfilled portions etc.
e) When the pipe line crosses a Hillock, it goes up the inclined plane and from peak runs down the slope. The up-going line is subjected to a sort of compression due its own weight due to sliding tendency or tension due to pulling effect, down the plane. The stresses due to any of these effects should be estimated and provided for.
Corrosion Allowance: In normal in-plant piping, standard corrosion allowances are specified for various duties in different design codes. Cross Country pipe lines run over a long distance and the leaks on any account cannot be permitted. Hence extra corrosion allowance is specified for cross country pipelines. In any case minimum of 3 mm or as specified, whichever is greater, is provided as corrosion allowance.
Design codes generally followed for cross-country piping (in addition to normal codes for all piping)
ASME B-31.4/ 31.8 for thickness Design.
API – 1104 for welding and related tests specifically on cross-country Gas and Oil lines.
API – 5L for material of construction.
Generally, in non-hazardous fluid line, say water lines, Breather valves (pressure and
Vacuum) are provided at he highest points, say on Bill-top, to prevent ‘Air-lock’ or to suck-in Air in case vacuum or cavitation takes place. But in pipelines carrying Gas or Hydro-carbon liquids like crude oil, refined oil, naptha, ethylene, propylene etc. No Breather Valve is permitted any where on the line. This is because the hazardous liquid cannot be allowed to come out into the atmosphere and Air (which contains oxygen) cannot be allowed to be sucked-in as the fluid may combine with atmospheric oxygen and catch fire. Anytime the line is to be commissioned, the fluid to be carried is filled into the pipeline by first passing the pig from supply end. There are no chances of Air-Lock.
1.1 Cleaning / Scraping external pipe surface.
1.2 Priming with synthetic primer.
1.3 First Coat of coal Tar Enamel.
1.4 First layer of Inner Wrapping of Fiberglass tissue fabric.
1.5 Final Coat (2nd Coat) of Coal Tar Enamel.
1.6 Outer wrap of coal-tar impregnated Fiberglass tissue Fabric.
1.7 White Wash.
2 Regulation: All materials conform to AWWA C – 203-86 or BS – 4164-1987 or ASTM Standards.
3. Limitations: Coal-Tar enamel based coating / wrapping should withstand the liquids carried
up to Temperature of 60 deg C.
4. Inspection and Testing: Applied coating / wrapping should be tested by SPARK TEST to be applied with HOLIDAY DETECTOR. Any sections found defective with pin-holes, cracks, internal hollows, pockets, wrinkles, air pockets, less thickness etc. should be removed, redone and retested until they are made defects-free.
5. Handling and Placing: The pipes already coated / wrapped should be carefully lifted using special strap-type lifting clamps to prevent concentrated loads and forming dents or depressions. The straps shall be of flexible but strong and soft rubber sheet, wide enough to distribute the self weight of lifted pipes within the intensity which coating / wrapping can withstand without getting damaged or depressed.
These pipe lines are protected against corrosion by external coating systems and cathodic protection. Various coating systems have been tried over the past 45 years and they have evolved with time and with innovation of new materials. Today, five main coating systems are commonly used for pipelines: three layer PE (3LPE), three layer PP (3LPP), fusion bonded epoxy (FBE or Dual FBE), coal tar enamel (CTE), asphalt enamel and polyurethane (PUR). The different systems are specified by pipeline owners and consultants based on various factors, including short-term cost, long-term cost, captive usage, regional availability of the coating material, control on handling, transportation and installation of pipelines, and technical reasons.
3LPE coating is dominant worldwide, with 50 per cent market share, for onshore pipelines, with the exception of North America. The trend is increasing with a greater number of projects coated with 3LPE in China, India and the Middle East. The increased acceptance of 3LPE is due to its broad operating temperature range (from -45°C to + 85°C) and ability to withstand very rough handling and installation practices without damage to the coating.
3LPE systems consist of an epoxy primer, a grafted copolymer medium density (MDPE) adhesive to bond the epoxy primer with a high density (HDPE) topcoat. 3LPP systems are recognized as excellent systems for offshore projects with elevated operating temperature (0°C to +140°C) and extreme mechanical stress on the pipes. Recent projects in the North Sea, Africa, Gulf of Mexico and Arabian regions have set new standards for 3LPP coatings, which provide access to deeper gas and oil fields. 3LPP system consists of an epoxy primer, a grafted copolymer PP adhesive to bond the epoxy primer with a PP topcoat.
FBE is dominant in North America, United Kingdom and a few other countries but the trend is declining in favor of 3LPE and PP Systems. Some pipe line owners have graduated from coal tar coating to Dual FBE as the cost has become quite competitive after increases in coal tar prices.
Coal tar and asphalt enamel are both still used in some countries. For many refineries, which have their own pipelines, coal tar is the cheapest coating option, being their own product. Both systems are declining and suffer from health and environmental concerns.
PUR systems are mostly used for pipeline rehabilitation projects or girth weld coating. PUR systems also suffer from health concerns.
In this context, PP systems with up to seven layers are increasingly gaining ground for technically challenging deep sea projects, with very high operating temperature, where several functional PP layers are used for thermal insulation foams. These foams, apart from insulation properties, should have high compressive strength so that they do not collapse under high external pressure in deep sea environment.
HDPE and PP based systems offer excellent mechanical protection and long-term ageing performance.
A high level of investment in research and development in close co-operation with customers ensures the continual development of innovative new products and pipe system solutions. Several new products are under development including a PE top coat with very high resistance to slow crack growth, machine applied PE for field joint coatings, PP weight coating and PP injection molded systems for field joint coating. The result of this approach is a long pipeline service life with minimum maintenance cost for the pipe line owner, fast production and high output for the pipe coater, easy installation without repairs for the installers and peace of mind and reliability for the engineering consultant.