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Aug. 07, 2012 - Boulder, Colorado

Spoolable Composite Pipe Testing - API15S


Authored by Dr. Bryan Hauger, Microbac Laboratories, Inc., Hauser Division

The history of oil and natural gas production has seen many innovative technologies develop to address the needs of the marketplace – leak-free, no corrosion, high pressures, rugged terrain etc.  Spoolable composite pipe, described by the API15S standard, is a significant innovation that uniquely addresses the needs of energy production because it combines the beneficial attributes of plastic pipe with a much higher pressure capacity than any mono-layer plastic pipe.  As detailed in the API15S standard, extensive testing is required to qualify both the materials used and the final construction in order to ensure a durable pipe that is capable of being coiled for shipping efficiency while still providing a high pressure capability for many years of service life.  Microbac Laboratories, Inc., Hauser Division has developed extensive capability to provide the required API15S testing – both for the materials of manufacturing and the finished products.  Let us first take a closer look at the products and the markets that they serve.

Composite pipe simply means that more than one material of construction is used – a high strength material with some chemical compatibility limitations and a lower strength plastic product often with extraordinary chemical resistance.  The innovation was to find a way to combine these two disparate materials into a pipe that can be coiled on a spool for highly efficient storage and shipment such as is normally obtained for solid wall plastic pipe.  A network of high strength fibers interwoven in highly designed structures are combined with a barrier to protect them from the corrosive water and petrochemicals, allowing the best of both worlds.  The barrier layer is commonly the same high durability polyethylene material used in solid polyethylene pressure pipe.  Different suppliers have used a diversity of high strength fibers including steel, glass fibers and many different types of thermoplastic materials.  Clearly a single standard that incorporates these disparate materials, as well as addressing the methods of demonstrating both the strength capacity of the finished composite pipe and its durability is a ambitious task, but one that has been accomplished with excellent results by the API15S standard.

A better understanding of the diversity of the construction materials used in API15S pipe can be obtained by reviewing the testing required by the standard.  For example, the materials selection section for the polymeric liner discusses polyethylene, PEX, polyamide, and PVDF.  Moreover, it is recommended that manufacturers provide a summary of data for the material properties outlined in Table 11 of API Specification 17J.  Mechanical property tests recommended by that standard include characterization of creep resistance, tensile properties for strength and strain, compressive strength, impact strength, stress relaxation properties, Young’s Modulus, abrasion resistance, Density, Fatigue testing and Notch sensitivity.  Thermal property tests recommended by that standard include measurement of the coefficient of thermal conductivity and expansion, heat distortion temperature, softening point, heat capacity and glass transition temperature.  Additionally, testing is conducted related to permeation characteristics, compatibility to the fluids used and aging tests.  The tests on the polymeric liner materials only qualify those materials for use in a structure which must also be comprehensively tested in a proscribed qualification program.

Additional qualification testing is required by API15S for the pipe, end fittings, and couplers.  The pipe is subjected to extensive hydrostatic pressure testing at the maximum design temperature as described in ASTM D2992 – Procedure B including at least 18 test samples with at least one sample being tested past 10,000 hours.  These data are then analyzed to obtain the long term hydrostatic pressure capability of the pipe at the time basis is used for design.  Service factors are then used to establish the maximum pressure rating and maximum service pressure.  The short term burst pressure is also tested in accordance with ASTM D1599 – Procedure A.  In applications where the pipe service is anticipated to experience pressure cycles in excess of 20%, then additional testing in accordance with ASTM D2992 – Procedure A may be required.  Elevated temperature testing is conducted to ensure that other failure modes do not occur at periods of time following the maximum time used in testing and the time used for the design.  Testing is also conducted to determine the maximum external pressure capability of the pipe by crush testing as described in ASTM D2412.  Additionally, the resistance to UV exposure of the pipe shall be demonstrated.  The resistance of the pipe to bear impact loads and still hold pressure is documented.  Changes in the pipe length as a result of pressure and temperature are also measured.  In addition to parallel testing with the pipe, end fittings and couplers are required to be tested for their capability to bear an axial load when installation is planned to pull on already installed end fittings or couplers.  The trust that end-users place in these piping systems and also their positive service history is driven by the extensive testing of API15S pipe, end fittings and couplers by third-party laboratories.

The testing required for API15S extruded polymeric material qualifications is very broad and Microbac Laboratories, Inc., Hauser Division conducts many of these tests in accordance with its ISO 17025 scope of accreditation.  Creep resistance is characterized through ASTM D2990 Test Method for Tensile, Compressive and Flexural Creep and Creep Rupture of Plastics.  Tensile properties, including Young’s modulus, are measured in accordance with ASTM D638 Test Method for Tensile Properties of Plastic.  Hardness of materials may be measured using Durometer Hardness testing in accordance with ASTM D2240.  ASTM D695 Test Method for Compressive Properties of Rigid Plastics provides for the measurement of the compressive strength of the liner materials.  Impact strength and notch sensitivity are tested in accordance with ASTM D256 Test Method for Determining the Pendulum Impact Resistance of Notch Specimens of Plastic. 

Microbac’s Hauser Division tests density by ASTM D792 Test Methods for Density and Specific Gravity of Plastics by Displacement, as well as by ASTM D1505 and ASTM D1622.  Heat distortion temperature is characterized by ASTM D648 Test Method for Deflection Temperature under Flexural Load.  E1269 Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry provides the test protocol for measuring the heat capacity of the materials. E1356 Test Method for Glass Transition Temperatures by Differential Scanning Calorimetry or Differential Thermal Analysis provides the technical basis for the determination of glass transition temperatures.  ASTM D1693 is the Test Method for Environmental Stress Cracking of Ethylene Plastics.  ASTM D570 is the Test Method for Water Absorbency of Plastics.  Microbac’s Hauser Division is capable of measuring stress relaxation by ASTM E328, abrasion resistance by ASTM D4060 and softening point by D1525, as well as measuring the coefficient of thermal expansion by ASTM D696.  This list of tests, required by API15S, is summarized in Table 1.

The qualification testing requirements for the pipe, end fittings and couplers are similarly challenging.  Crush testing by ASTM D2412, short term burst pressure by ASTM D1599 and hydrostatic testing by ASTM D1598 are included in Microbac’s Hauser Division’s scope of accreditation.  The line pressures and high temperatures required to challenge these spoolable composite pipes are higher than many laboratories can achieve.  Microbac is able to conduct hydrostatic testing in environmental chambers capable of going well in excess of 150°C.  Additionally, Microbac has recently invested in high pressure testing stations capable of testing up to 4500 psi line pressure which provide the required pressures to conduct ASTM D1598 and D1599 testing on these high pressure piping systems.  Microbac Laboratories, Inc. is well positioned to meet the testing needs of spoolable composite pipe manufacturers.

For more information on testing spoolable composite pipe or its component polymers and to see how Microbac Laboratories, Inc. can assist you with any composite pipe related inquiries, please contact Dr. Bryan E. Hauger at Microbac’s Hauser Division at 720-587-7880, or Bryan.Hauger@microbac.com.

 

Table 1.  Analyses Required for API15S Extruded Polymeric Materials that are within the capabilities of Microbac Laboratories, Inc., Hauser Division.

Characteristic

Tests

Test Method

Mechanical/
physical properties

Resistance to creep

ASTM D2990

Yield strength/elongation

ASTM D638

Ultimate strength/elongation

ASTM D638

Stress relaxation properties

ASTM E328

Modulus of elasticity

ASTM D638

Hardness

ASTM D2240

Compression strength

ASTM D695

Impact strength

ASTM D256

Abrasion resistance

ASTM D4060

Density

ASTM D792

Notch sensitivity

ASTM D256

Thermal Properties

Coefficient of thermal expansion

ASTM D696

Heat distortion temperatures

ASTM D648

Softening point

ASTM D1525

Heat capacity

ASTM E1269

Glass Transition Temperature

ASTM E1356

Compatibility and aging

Environmental stress cracking

ASTM D1693-05

Water absorption

ASTM D570