PIPELINES - A simplified step by step pipeline construction exercise, incl. manhours & costs. (Note: This page continues use of Excel downloads, to be replaced by stand-alone calculators in due course. However, in the meantime a multi-purpose EMMA will serve admirably to track excavation, or stringing, or welding, or laying, or backfilling, or all manpower requirements)
This step by step assessment of the work scope, manhours and equipment needed to construct a buried steel pipeline, using MS Excel calculation files* that can be downloaded for each step, will culminate in a ball-park estimate of the total project cost. In addition, based on a single operating crew/equipment unit, an activity duration for each will be calculated**. If the user does not have Excel, the illustrations can be used as a guide to calculating hours and costs 'manually'. As a minimum, the following information will be required.
*Note: Where 0 appears in red font a quantity will be required, minimum 1.
**Note: If the activity duration which results is not likely to be acceptable, an increase to working hours/days and/or an increase to the number of crews can be changed, in order to achieve a reduced duration. Example 1 (right) assumes 8 hrs per day, 5 days/week, with one crew(2 teams) which will take 99 work days or 19.8 weeks to complete. Example 2 increases the working hours/days and adds a second crew, reducing the schedule to 44 working days or 7.3 weeks.
See Enbridge video (Above) for an overall introduction to stages of pipeline construction.
If interested in pipelining, the reader is invited to put the following series of calculation files to the test, by producing a basic ball-park construction estimate for a 20" sch. 40 seamless steel pipeline over a distance of 100 miles in Arizona, USA. At the end of the exercise, comparison with recent data will be possible, allowing the reader to decide whether his/her estimate was in the right 'ball-park' (ie +/- 25%).
Time for a pipeline route survey and the cost thereof is often under-estimated, particularly if undertaken across country in extreme weather conditions, through dense vegetation, or where security is a factor. Learn more from Mustang.
Clearance of a pipeline route can involve the width of a highway (say 15 -30 metres), because space is required throughout its length to excavate the trench, stockpile soil, set down pipe lengths alongside the trench for aligning, welding, wrapping etc., and set up the side booms for lowering. In addition a roadway is required to one side for traffic moving up and down the route, plus laydown and maintenance areas at strategic locations. Special equipment can be needed through difficult terrain, river crossings etc
Soil conditions might vary along the length of a pipeline's route, ranging from sand to rock, influencing the hours that will be taken to excavate these particular sections. For maximum accuracy, therefore, an estimate should be divided up as appropriate. Where sandy conditions exist, sloping sides of the trench will be necessary, for safety reasons, but excavation will proceed smoothly. In firm soil, vertical sides might be permissable, whereas in rock progress could be very difficult and slow. Good quality excavated material should be suitable for backfill, with surplus having to be disposed of by some means, possibly by spreading local to the route. Otherwise some backfill material might have to be sourced and brought in. See VIDEO below of trenching M/C in action.
The first stage involving the handling of piping is to uplift pipe lengths from storage areas, transport them along the pipeline route and place them roughly where they will be aligned, welded and wrapped, using sleepers or other means to support above the ground. This operation is known as 'stringing' the pipes and would normally be done after trenching, but not always. The number of storage areas will depend upon the length of pipeline and the rate of pipe stringing upon the number of crews operating along the route. This VIDEO by Jason LaValley demonstrates a stringing operation admirably.
Common practice is to perform all welding together of pipe lengths at ground level, followed by application of cathodic protection, before lowering long sections (Can be 1km) of the pipeline into the trench. This VIDEO demonstrates the latest equipment used to align large diameter pipes in pipelines.
Wrapping is just one form of protection for buried pipelines and may all be done in the field, usually after welding and before lowering into the trench. Alternatively, pipe lengths can be wrapped before delivery to site, leaving only the area of the weld unwrapped, for completing in the field, before or after lowering. This VIDEO demonstrates a small diameter pipe being wrapped in the field. Other forms of piping protection are described by this DENSO pdf file.
Pipe lowering operations normally will be carried out by one or more side booms, together with associated equipment items, the numbers depending on the lengths of segments that have been prepared at ground level. This VIDEO by Lance Romberg shows a long section of a pipeline being lowered into its trench using 3 sidebooms. This article published by Pipeline International discusses various aspects of lowering equipment. Depending on circumstances in the field, lowering can be done using excavators, cranes etc.
Following final NDT and hydrotesting of the pipeline, backfilling and compaction takes place in layers, using original excavated material if of good quality, or material screened through a 'padder', otherwise more suitable soil or sand imported from elsewhere. This article in Pipelines International discusses various aspects of backfilling pipelines including equipment used. The following video covers lowering, testing and backfilling to high standards.
EXERCISE CONCLUSIONS - If the reader has opted to produce the suggested basic construction estimate, the following info. will be of interest:
NOTE: If only basic hourly rates were used for labour and heavy equipment in the above calculations, further allowances will have to be made for items such as overtime premiums, incentive bonuses, home leave, construction management and supervision, servicing and repairs, tools and consumables, transport and accommodations, contingencies, insurances, contractors' overheads and profit, all of which could compute to a factor of 3 or 4 times the basic costings.
HYPOTHETICAL PIPELINE COST BREAKDOWN
The cost tabulation below represents just one of a multiplicity of scenarios and degrees of difficulty that could apply to such a pipeline. The scope of front end activities would depend on whether obtaining approvals etc was to be a smooth, or long drawn out process. Values of equipment and materials would depend upon the pipeline's intended service. Weightings of listed construction activities could vary by +/-several percentage points, depending upon terrain, numbers of river crossings etc
Did your estimate come within the range $21m - $35m? If so, the exercise could be considered successful. Comments/clarifications welcomed.