How Corrosive Environments Affect Materials

We help end users and equipment vendors determine how equipment is affected by exposure to corrosive operating environments. Full-scale equipment components and full assemblies are often tested instead of coupons to account for the actual product characteristics, such as:

  • Size, type and distribution of manufacturing defects;
  • Material surface finish;
  • Residual stress distribution; and
  • Manufacturing methods such as welding, heat treating and forming.

Pressure, load and temperature of the operating environment are also applied to the equipment during testing. Full-scale specimens are usually used to account for the complex operating stress state. It is difficult to simulate these stresses and how they interact with the corrosion processes in simple material coupons.

Testing can include different corrosive environments depending on the expected operating conditions and the susceptibility of the material. Typical environments used for corrosion testing include:

  • NACE solutions;
  • Corrosive gases – hydrogen sulfide, carbon dioxide;
  • Hydrocarbon gases – free gas, in solution;
  • Hydrocarbon liquids – crude oil, diluted bitumen, oil-based drilling mud, refined products; and
  • Salt spray and brine.

The materials that we have typically tested include:

  • Metals;
  • Fiber reinforced polymer;
  • Cement; and
  • Elastomers.

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Corrosion and Materials

Corrosive Environments

  • NACE Solutions
  • Sour – H2S, CO2
  • Hydrocarbons
  • Salt Spray

Materials

  • Metals
  • FRP
  • Cement
  • Elastomers

Metals: Validating Non-destructive Examination (NDE) Results with Direct Measurements

We test how corrosion damage in metal equipment components can result in cracking, pitting and general wall loss. Cracking can include different mechanisms where corrosion acts with the operating stress in the equipment:

  • Sulfide stress cracking (SSC);
  • Stress corrosion cracking (SCC);
  • Caustic stress corrosion cracking (CSCC); and
  • Hydrogen induced cracking (HIC).

We also evaluate the performance of NDE methods used to detect and characterize defects in metal components. This includes side-by-side, independent tests of NDE methods, such as magnetic flux leakage (MFL), ultrasonic (UT) and alternating current potential drop (AC-PD).

We compare the NDE results to direct measurements of the defects. This can include real defects in equipment removed from service or precise manufactured defects that mimic cracks, pits and general wall loss. The performance of the NDE method is reported in terms of probabilities and measurement cccuracies.

Probabilities

  • Probability of detection (POD)
  • Probability of identification (POI)
  • False discovery rate (FDR)
  • Radial position mirroring (RPM)

Measurement Accuracies

  • Sizing (height)
  • Sizing (length)
  • Position (axial)
  • Position (depth)

We provide the results of NDE validation tests to asset owners to assist them in evaluating the value provided by different inspection techniques. The NDE service providers use the same results to improve the reliability and accuracy of their systems.

We also run custom full-scale tests that simulate a corrosive operating environment and representative loading conditions. Examples of these tests include:

  • Slow strain rate tests of full-body coiled tubing specimens to simulate low-cycle / plastic fatigue;
  • Four-point bend testing of premium well casing connections;
  • HIC growth in a glycol separator;
  • Hydrogen embrittlement of steel armor wires in flexible risers and flow lines; and
  • Cyclic pressure testing to determine remaining life of pipe with SCC.

Fibre-reinforced Polymer (FRP): Ageing and Fluid Infiltration

We have conducted various tests to determine how FRP products degrade over time. Two degradation mechanisms have been identified in glass-fibre composites: ageing and creep-rupture. Both are associated with a decrease in mechanical strength over time with exposure to the operating environment. Ageing occurs without applying stress to the material. Creep-rupture occurs when the structure is under constant load. The level of degradation from these damage mechanisms is a function of the:

  • Polymer matrix;
  • Fibre material;
  • Fibre interfacial properties; and
  • Operating environment chemistry and temperature.

Strength loss in glass-fiber reinforced polymers generally increases with exposure to water and elevated temperatures. Applying load can cause stress corrosion cracking of the glass fibers which accelerates the loss of strength.

Some fatigue loading tests on composite structural panels include salt spray to simulate marine operating environments.

In some cases, a dry fibre wrap (with no resin) is used to provide hoop strength in a pressure vessel or pipe. A thick polymer sheath is applied over the fibre wraps to prevent water from contacting the fibres. Long-term ageing tests are performed to determine the effectiveness of these coatings. The impact of exposure to water is assessed by conducting burst tests on new and aged pipes.

Cement: Evaluating the Long-term Sealability

We use various test methods to assess how cement is affected by conditions deep underground. The primary focus is on the long-term durability of cement in these conditions. For instance, cement is used in oil and gas wells to prevent liquids and gases in deep formations from contaminating shallower drinking water sources. Other applications include isolating wells used for sequestering underground CO2 and storing nuclear waste.

The mechanisms that damage cement include:

  • Elevated temperature;
  • High salinity brine; and
  • Acid gases including CO2 and H2S.

Some materials are being added to traditional cement to enhance performance. This includes additives to minimize cracking by increasing the flexibility or tensile strength of the cement. Other additives give the cement self-healing properties to plug or close cracks after they form.

Other materials are being considered to replace Portland cement-based materials. These include:

  • Thermosetting resins;
  • Metal alloys;
  • Sodium silicate;
  • Salts; and
  • Geopolymers.

Testing programs include evaluating changes in the following material characteristics:

  • Permeability to gas;
  • Compressive strength at ambient and elevated temperature; and
  • Volume (shrinkage and swelling).

Elastomers: Evaluating Compatibility in Severe Operating Environments

We measure elastomer compatibility in different service environments. This can include exposing coupons to combinations of:

  • Hydrocarbon liquids and gases;
  • High temperature; and
  • High pressure.

Tests may also include full-scale equipment with elastomer components. This can include sealing elements such as o-rings. Structural components, such as stators in progressing cavity pumps and drilling power sections, can also be made from elastomers.

Elastomer behaviour can be very complex. Operating environments can include changing pressure, temperature and chemical exposure. For instance, an elastomer component operating in an oil well may:

  • Thermally expand and soften due to elevated temperature;
  • Swell due to hydrocarbon and gas penetration; or
  • Shrink and harden due to leaching of some components of the elastomer.

The rate of change of the operating conditions can also affect the elastomer response. Explosive decompression can occur by removing pressure or load rapidly after the elastomer has been exposed to gases.

In elastomer material tests, coupons are exposed to the service environment for a period of time. The specimen is then removed from the environment to measure how the exposure has affected the material properties and dimensions. These tests can show if the elastomer is permanently changed by the operating environment. However, the tests do not indicate the actual condition of the elastomer while operating. In addition, the material properties are tested after the specimen has gone through a decompression cycle that could also alter its properties.

We have developed specialized testing methods to measure the dimensions of elastomer specimens continuously through a service cycle. These tests can show the initial compression of the elastomer as pressure is applied. Thermal expansion is measured as the specimen is heated. The rate of swell can be measured as the elastomer interacts with the chemical environment.

Specimens may also shrink as the test fluid leaches material from the elastomer. These tests can indicate whether the elastomer will stabilize in the environment or will continue to change in volume until it can no longer serve its purpose.

Finally, the elastomer dimensions can be monitored continuously during the decompression cycle. This information can be used to determine what decompression rate can be tolerated without damaging the elastomer.

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