Stess-tests, Hydrostests and Commisioning 

of high pressure large-diameter pipelines

Stress-test

The stress-test is a complex technologic 
operation performed on buried steel pipeline 
after its construction with the aim 
to reach the highest level of future operation 
safety and reliability as well as maximal 
operational lifetime

 

The Effect of New Pipeline Stess-test 

Stress-test PREPARATION  

STRESS-TEST PRINCIPLE

TEST and PROCEDURE

SKETCH OF stess-test

The Effect of New Pipeline Stess-test on top

  • critical defects are detected and propagation 
    of sub-critical defects is blocked

  • local stress peaks in the area with imperfect or damaged geometry are removed

  • residual stresses introduced during manufacture of pipes, welding, and construction of pipeline are reduced

  • operating safety is enhanced and lifetime 
    is extended in the pipeline

  • operating pressure of existing pipelines can be upgraded 
    on the basis of the test results

  • integrity and strength of the tested pipelines is substantiated

Stress-test PREPARATION on top

Before accomplishment of stress-test is on the base of concrete data about material individual pipes and about pipeline path maked detailed project of commisioning, whole technological procedure and timetable of works.

STRESS-TEST PRINCIPLE on top

  • the stress- test is controlled water 
    pressurization of the tested pipeline section 
    to the pressure level which causes a stress 
    close to the yield point in the pipe wall

  • local residual stresses in the pipe wall 
    caused in the course of manufacture 
    and construction process 
    are redistributed and minimized

  • zones of plastic deformations generated 
    in defective areas cause sub-critical defects 
    to become blocked and critical defects to fail

Test and Procedure on top

  • batching pigs are placed inside temporary pig traps

  • the temporary pig traps 
    are welded to the pipeline section to be tested

  • the line is filled with water; 
    the batching pig driven ahead of the water forms 
    an efficient interface and ensures 
    that the line is properly flooded

  • water quantity is recorded during entire filling operation

  • the stress-test is carried out 
    according to the VdTUV Merkblatt 1060 
    or according to our special most recent requirements: 
    pressure, volume, and temperature of the water 
    are measured and recorded during the test period 
    and the entire course of the stress-test is controlled by computer

  • water is removed from the line with batching pigs 
    driven by compressed air

  • the line is dried using foam pigs and drying to the dew point 
    under –4 °F or on the entrepreneur’s request
    also to the lower value (up to –94 °F)

The pressure test is an integral part of the procedure.

Sketch of Stress-test  

  1. complete pig trap   

  2. pressuring pumps;
    25 MPa, 220 l/m

  3. fillings pumps;
    4 m3/min

  4. auxiliary pumps; 
    4 m3/min

  5. mobile tanks; 
    30 m3

  6. measuring equipment

  7. control computer

  8. pressure gauges; 
    20 MPa, acc. 0,075 %

  9. turbine flowmeters;
    4700 l/min, acc. 0,2 %

  10. thermomethers;
    from –22 to +140 °F

  11. compressors;
    2 MPa, 1700 m3/hr

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