The main activities in the laboratory are the testing of structures, structural components and materials. Typical problems involve fatigue testing, ultimate strength and collapse testing, testing for serviceability, and advanced materials testing. Experimental work is often combined with analytical or numerical analysis.

A wide range of structural analysis programs are available for linear and non-linear static and dynamic analyses. These include special programs for fatigue and fracture mechanics analysis, and the collapse behaviour of intact and damaged structures.

The Marine Structures Laboratory is operated by MARINTEK, Div. of Structural Engineering in cooperation with Norwegian University of Science and Technology, Dept. of Marine Structures.

MAIN INSTALLATIONS
Strong Floor:

7 x 11 square meters, weigth 200 tons, maximum point load 2000 kN. Adjacent floor space approximately 500 square meters for smaller loads.

Hydraulic power:

Primary ring main 500 l/min, secondary ring main 50 l/min, 240 bar.

Acturators:

A range of servohydraulic acturators for static and dynamic testing, from 100 kN load capacity to a maximum load/stroke of 4000 kN/1000 mm.

Control system:

Several computerized systems for multi-acturator control, fatigue load simulation, data logging with on-line reduction and analysis.

Rig system:

Modular frame system which can be built to accomodate specimens and structural models with a wide range of shapes and sizes, under unaxial or multiaxial loading, and with load capacities up to 4000 kN.

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Fatigue testing:

High performance dynamic acturators with load capacities up to 2000 kN with hydraulic grips. A wide range of load programs, including randomized load sequences with variable or constant rms levels and variable signal bandwidth.

• environmental chambers for low temprature testing
• seawater testing with temprature control and cathodic protection
• testing of large structural models with automated crack growth monitoring

Steel rope testing:

Static and dynamic testing of heavy steel rope, with axial loading and specimen lengths of up to 7 meters.

Collapse testing:

Maximum load capacity 4000 kN, stroke 1000 mm in closed loop control. Large models can be tested under controlled conditions of multiaxial loading to obtain the buckling and collapse characteristics of intact and damaged structures.

Fracture testing:

Realistic models of wide plates, pipelines, risers, tether elements and tubular joints can be tested to fracture at tempratures down to -50 degrees.

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Rig for full scale dynamic testing of flexible pipe

• Configuration: Horizontal, in a test frame on the laboratory floor.
• Pipe model: Length 15 m flange-to-flange.
• Loading: Two independent modes of loading; tensile axial loading at one end, bending loading in opposite end.
  1. Bending load capacity: 1 MNm dynamic, 30 degrees tilt static, ± 30 degrees dynamic.
  2. Axial load capacity: 1.5 MN dynamic, 500 mm stroke dynamic.

• Load signal: State-of-art digital control electronics, computerised load generation. The system accepts any sequence of peaks and troughs, e.g. generated by a block program to be specified by Client.
• Pressure: Internal pressure of pipe up to 600 bar.
• Environment: Oil or water filled pipe model, ambient room temperature.

Instrumentation for measurement of:

• Number of cycles
• Internal temperature of pipe
• Temperature in outer armour layer
• Ambient temperature
• Internal pressure
• Applied tension
• Rocking angle
• Strain in outer armour layer

Facility for:

• Conditioning of pipe at 125 oC internal temperature, 500 bar pressure.
• Leak testing at 110 % of design pressure, ambient temperature.

Condition monitoring:

Condition monitoring of pipe during testing may be performed by Robit, using state-of-art methods:

• Eddy current inspection of outer tensile armour layers
• X-ray inspection of metallic components
• Acoustic emission for detection of development of fatigue or wear modes of failure
• The test rig complies with API requirements for full scale testing of flexible pipes.

Thermal Cycling Testing of Flexible Risers

MARINTEK has established a facility for testing of flexible pipes subjected to thermal cycling simulating shut-downs. By calibration to data inferred from field failures, a test procedure has been established in which the conditions of failed pipes are simulated. The temperature may be cycled by programmed profiles from -20 to 1300C. There are 10 slots for simultaneous testing of pipe models.

Using numerical simulation of the transient thermal response in flexible pipes subjected to various scenarios of shut-down (described below) test procedures are developed by which a wide range of field conditions may be simulated. More than 20 pipes have been/are being tested, from all three major suppliers of flexible pipe.

The test procedures which have been developed are in the process of being written into API guidelines.

Small scale test facility for flexible risers:

• Fully equipped structural laboratory for tests on flexible pipe components:
• Small scale tests of tensile armour, effects of fretting contact, wear, sea water etc.,
• Assessment of SN design curve.
• Dedicated test facility for wear testing of composite tensile armour
• Small scale tests of hoop stress profiles, component tests, fatigue and wear
• Fatigue and ultimate strength tests of armour components anchored in epoxy
• Wear of anti-friction layers, effect of elevated temperature

Design analysis:

The following is a short list of computer codes used:

• RIFLEX: Non-linear FE code for 3-D global analysis of pipe, static and dynamic analysis, frequency and time domain analysis, assessment of test parameters for simulation of operating conditions.
• CAFLEX: Pipe-wall analysis with assumed axisymmetric conditions.
• BFLEX: Stress analysis of tensile and hoop armour with arbitrary curvature gradient along pipe, fatigue analysis.
• General FEM: Component analysis, e.g. hoop stress profiles, end-fitting details, etc.

Thermal analysis of flexible risers

A computer code has been developed for calculation of transient temperature fields in a pipe with end fitting during temperature cycles. The computational model is based on the following elements:

OLGA (1989) is a computer code developed for analysis of two-phase transport of oil and gas through pipelines. The program calculates in time domain the separation of oil and gas, and the thermal conditions inside a pipe due to pressure release.

FAHTS (1995) - Fire and Heat Transfer Simulations in Framed Structures is a finite element code for analysis of heat transfer in time domain, taking into account heat transport by convection, conductance and radiation. Three-dimensional fields and transients can be calculated assuming rotational symmetry.

USFOS (1988) - Ultimate Strength Analysis of Framed Offshore Structures is a non-linear finite element code. Geometric and material non-linearities are accounted for.

The program suite is used for calculation of transient and stationary temperature distributions in a flexible riser system, and thermal forces in the different layers of the pipe including effects of end termination, bend stiffener and external environment. The program has been validated against realistic laboratory tests.

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