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PRCI Report 110
- Addition of Inhibitors to the Soil above Pipelines to Minimize Stress Corrosion Cracking
- Report / Survey by Pipeline Research Council International, 01/01/1977
- Publisher: PRCI
$148.00$295.00
L11777e
Battelle Memorial Institute
Need: Past research on the causes of pipeline failures in the field has shown that some failures were caused by stress-corrosion cracking. Subsequent work in the laboratory has identified a number of chemicals as being good inhibitors of stress-corrosion cracking of pipe steel in laboratory experiments that simulate those environments and conditions that might have caused cracking in the field. Pipeline companies need to understand what chemical inhibitors can be used to mitigate stress corrosion cracking in pipelines.
Result: A research investigation was undertaken to determine the rate of movement of selected inhibitors in various soils. Most of the research dealt with soluble phosphates. The use of chromates as soil additives was not considered feasible because of the toxicity of chromates, and silicates were not as effective as phosphate in inhibiting stress-corrosion cracking. The investigation consisted of the following four parts:
(1) A brief literature survey on the movement of phosphates in soils
(2) A laboratory investigation of the horizontal movement of phosphates and silicates in selected soils
(3) A limited field study of the downward movement of phosphates in a clay soil
(4) A laboratory investigation of the downward movement of phosphates in various soils.
Seven of the best inhibitors are Sodium chromate (Na2Cr04), Potassium dichromate (K2Cr207), Zinc chromate (ZnCr04), Sodium monobasic phosphate (NaH2P04 H20), Calcium monobasic phosphate [Ca(H2P04)2 H20], Sodium tripolyphosphate (Na5P3010), Potassium silicate (9% K20 and 20% Si02 in water). Under laboratory conditions, these chemicals retard the initiation of stress-corrosion cracks and effectively retard the growth of existing stress-corrosion cracks. Very good protection has been obtained when the liquid environment contained 1.0 percent phosphate.
Benefit: During installation of a new line, it may be possible to incorporate some of these chemicals into the coating system and/or mix them with the soil nearest the pipe. These systems probably would provide adequate protection against stress-corrosion cracking for some finite period of time, if properly applied to new pipelines. Protection of existing pipelines would be more difficult. Highly soluble inhibitors added to the surface soil above the pipeline might percolate down to, and around, the pipe in time, but such soluble compounds would continue to move and, hence, ultimately would move away from the pipe. Periodic additions to the surface soil might provide continuous protection of the pipeline. Less-soluble compounds could be injected into the soil within a few inches of the top of the pipe, but the inhibitor would need to travel down and around the pipe to protect the entire pipe periphery.
Battelle Memorial Institute
Need: Past research on the causes of pipeline failures in the field has shown that some failures were caused by stress-corrosion cracking. Subsequent work in the laboratory has identified a number of chemicals as being good inhibitors of stress-corrosion cracking of pipe steel in laboratory experiments that simulate those environments and conditions that might have caused cracking in the field. Pipeline companies need to understand what chemical inhibitors can be used to mitigate stress corrosion cracking in pipelines.
Result: A research investigation was undertaken to determine the rate of movement of selected inhibitors in various soils. Most of the research dealt with soluble phosphates. The use of chromates as soil additives was not considered feasible because of the toxicity of chromates, and silicates were not as effective as phosphate in inhibiting stress-corrosion cracking. The investigation consisted of the following four parts:
(1) A brief literature survey on the movement of phosphates in soils
(2) A laboratory investigation of the horizontal movement of phosphates and silicates in selected soils
(3) A limited field study of the downward movement of phosphates in a clay soil
(4) A laboratory investigation of the downward movement of phosphates in various soils.
Seven of the best inhibitors are Sodium chromate (Na2Cr04), Potassium dichromate (K2Cr207), Zinc chromate (ZnCr04), Sodium monobasic phosphate (NaH2P04 H20), Calcium monobasic phosphate [Ca(H2P04)2 H20], Sodium tripolyphosphate (Na5P3010), Potassium silicate (9% K20 and 20% Si02 in water). Under laboratory conditions, these chemicals retard the initiation of stress-corrosion cracks and effectively retard the growth of existing stress-corrosion cracks. Very good protection has been obtained when the liquid environment contained 1.0 percent phosphate.
Benefit: During installation of a new line, it may be possible to incorporate some of these chemicals into the coating system and/or mix them with the soil nearest the pipe. These systems probably would provide adequate protection against stress-corrosion cracking for some finite period of time, if properly applied to new pipelines. Protection of existing pipelines would be more difficult. Highly soluble inhibitors added to the surface soil above the pipeline might percolate down to, and around, the pipe in time, but such soluble compounds would continue to move and, hence, ultimately would move away from the pipe. Periodic additions to the surface soil might provide continuous protection of the pipeline. Less-soluble compounds could be injected into the soil within a few inches of the top of the pipe, but the inhibitor would need to travel down and around the pipe to protect the entire pipe periphery.
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