Sobre el reconocimiento

It is proposed to perform a series of laboratory tests to measure corrosion damage as a function of soil type and microbiological variables. The tests will cover a range of conditions to simulate realistic field conditions, sterile conditions, and environments supplemented with bacteria and/or nutrients.The work scope spans over two years.

1. Assemble a matrix of 60 test cells representing a welded pipe sample with crevice under a range of soil, bacteria, and nutrient environments.

2. Allow bacteria to grow and measure corrosion damage after 6, 12, and 18 months.

3. Calculate corrosion rates based on time of exposure and environment to predict realistic MIC rates on buried pipelines.

A schematic of the test panel is shown in Figure 1. The panel will be approximately 4 inches, and cut from a section of pipe so that the weld (ERW is proposed) passes through the middle of the sample. The specimen will be flattened by a press so that a cylindrical test cell can be placed on the surface and sealed. Other than solvent cleaning to remove organics, minimal surface preparation will be conducted to preserve the structure of the surface. If possible, a thin walled pipe sample will be selected allowing weight loss measurements. A small section of polyolefin will be placed on the front of the panel forming a crevice like what might be found under disbonded coating on a field joint.

The test cell assembly is shown in Figure 2. A cylinder will be placed on the test panel and sealed with gasket material. The cylinder will be filled with soil, and the top will be sealed with a panel. A small port will be added so that bacteria and/or nutrients can be added during the test. This port will contain a 2 micron filter to prevent the entry of bacteria. For the cells in which bacteria will be introduced, a seal will be used that allows the use of a syringe without contaminating the cell.

A total of 60 cells will be constructed according to the test matrix shown inTable 1. . Four soil types will be tested:

4. The first will be soil collected from a pipeline dig site where MIC is suspected to have occurred. This is intended to most closely simulate a field environment known to have the ability to support MIC.

5. Sandy soil will be used to represent a porous and permeable material.

6. Clay will be used to represent a tight material with little void space and poor ability to transport biological or chemical materials.

7. Water will serve as a laboratory control sample. Use of water will allow visual inspection of the test panel throughout the test period.

Five bacteria related environments will be tested for each soil type:

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8. The first environment will be sterile. The test cell and soil will be sterilized by autoclaving, any restoration of water will be sterile, and the cell will be sealed using a 2 micron filter (not allowing bacteria to pass).

9. Fresh native soil will be used as the most natural of environments. Soil samples will be collected from field locations, and no attempt will be made to add bacteria or sterilize. Proper handling procedures (e.g., chilling) will be used to transport the soil so that any native bacteria are not destroyed during transport.

10. Nutrients will be added to the native soils to allow naturally resident bacteria to have access to food. This will simulate a condition of native bacteria with plentiful food source. One drawback to using nutrients is that previous testing has shown that planktonic bacterial growth can be stimulated over the preferred sessile bacteria that attaches to a surface and causes corrosion.

11. A fourth test will have bacteria added without nutrients. This simulates the condition of a natural soil environment and ensures that bacteria associated with corrosion are present. At minimum, the cell will be inoculated with two bacteria. Sulfate reducing bacteria (SRB) will be added because it is most frequently associated with corrosion damage.

In addition, a slime former will be added because MIC due to SRB is almost always associated with a biofilm dominated by slime. The slime allows a local environment to exist underneath it so that the anaerobic SRB is isolated from oxygen, and the corrosive metabolic products are concentrated under the film. Inoculation with acid producing bacteria (APB) is also preferred in the test because biofilms associated with corrosion are believed to be a complex matrix of bacteria including APB.

12. The last test cells will be inoculated with bacteria and contain excess nutrients. This environment will ensure bacterial growth in all soil environments.

Three cells will be assembled for each environmental combination giving a total of 60 tests. The triplicate cells are intended to allow measurement of corrosion (and bacteria) after three time periods so that corrosion rate can be calculated. It is expected that the corrosion rate will not be constant over the test period. The longest test period will be 18 months. This long period is considered necessary because previous work has shown that the period for bacteria to attach themselves to a metal surface, grow to form a biofilm, and generate corrosive metabolic products can take a period of several months. The first two cells will be disassembled after 6 months and 1 year.

Each panel will be evaluated for corrosion and bacterial activity. Corrosion will be measured by pit depth measurements and, if possible, weight loss. Bacteria counts will

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CC Technologies Laboratories, Inc.

be taken and a qualitative characterization of the biofilm will be made. The distribution of all observations will be noted with respect to the bare area and position down the crevice.

Table 1. Test Matrix Initially

Sterilized Fresh Native Nutrient

Supplement Inoculated

Inoculated &

Nutrient Supplement Field Soil 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo Sandy Soil 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo Clay 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo Water 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo 6,12,18 mo

Figure 1. Test panel with weld and polyolefin crevice. Circle represents test cell containing soil. Panel size is approximately 4 inches.

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Figure 2. Test cell assembly. A cylindrical cell sits on a flat test panel and is filled with soil. The top is sealed.

DELIVERABLES

The final deliverable will be a report documenting the results of the work and summarizing the conclusions. An interim report will be provided at the end of year 1, and quarterly reports will be provided.

SCHEDULE

The entire project will be completed within 24-months. Figure 3 gives the project schedule for the individual tasks.

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Months

0 6 12 18 24

Collect Materials Assemble Test Cells Run 6 Month Test Interim Report Run 12 Month Test Run 18 Month Test Final Report

Figure 3. Project Schedule