Workflow and input data

Stages of work

The general workflow of the integral method.

1. 1

   Data analysis

   Analysis of design, as-built and operational documentation, engineering survey materials, certification records and results of previous diagnostic inspections.

   Design documentation

   • general data
   • route plan and profile
   • specifications of pipes, fittings, shut-off and control valves

   As-built documentation

   • working drawings
   • certificates for installed pipes, fittings, shut-off and control valves

   Operational documentation

   • operating modes: inlet and outlet pressure
   • operating modes: inlet and outlet temperature
   • failure records (incidents, leaks) and repairs over the entire service period
2. 2

   Building the mathematical model

   A spatial digital model of the pipeline is built on the results of stage one.

3. 3

   Infrasound field measurements

   Inspection of above-ground process pipeline sections with infrasound instruments. Linear accelerations and angular velocities are recorded along three axes; the records yield the actual dynamic characteristics, loads and external effects.

4. 4

   Solving the set of dynamic problems

   Calculation of displacements and forces across pipeline elements, dynamic loads and the stress–strain state in every cross-section.

   Dynamic loads acting on the pipeline

   • steady and variable components of internal pressure
   • weight of the pipe and the transported product
   • thermal deformations
   • wind, snow and other transverse loads
   • displacement of support assemblies

   Causes of out-of-spec stress–strain state

   • high cyclic loading of internal pressure
   • actual external loads exceeding design assumptions
   • construction deviations from design decisions on pipeline stability
   • deviations in position and support conditions during operation

   Sections with reduced stiffness

   • geometry defects: transverse corrugations, longitudinal folds, dents
   • weld defects
   • pipe wall defects: general corrosion and erosion metal loss, cracks
5. 5

   Residual life calculation

   Determination of the safe operating period for the structure as a whole and for its individual elements, identification of the faults that limit that period and of their causes.

   The calculation accounts for

   • structural parameters of the pipeline
   • properties of pipe metal and welded joints governing resistance to steady and variable loads
   • the dynamic stress–strain state
   • defect parameters from previous inspections (where none are available, the calculation assumes the largest defect that diagnostic inspection would not detect)

   Ranking elements by safe operating period

   • continued operation at design modes carries unacceptable risk — the fault is remedied as soon as possible
   • the safe operating period is shorter than the interval to the next inspection minus repair time — the work enters the plan
   • the safe operating period exceeds the interval to the next inspection — no repair is required before it

   Recommended compensating measures

   • elimination of pipe defects
   • correction of faults in fixing and support
   • correction of faults in corrosion protection
   • engineering protection of the pipeline
   • a combination of the above
6. 6

   Recommendations

   Recommendations on the timing and methods of eliminating defects and damage, on engineering protection and safe operation, plus input for repair and inspection plans.

Input data for the digital model

The information the pipeline digital model is assembled from. Missing items do not block the work: gaps are covered by engineering margins, at the cost of calculation accuracy.