Differences in Near-Neutral pH Crack Growth Behavior Between Oil Pipelines and Gas Pipelines and Corresponding Crack Growth Mitigation Strategies
Bibliographic record
Abstract
Oil pipelines and gas pipelines operations result in very different pressure fluctuation schemes due to different compressive properties of liquids and gases. Liquid fluids such as oil are less compressible and pressure fluctuations during oil pipelines operations are more frequent and vary over a wide range of magnitudes and frequencies, compared with those during gas pipelines operations. Despite the differences in operating conditions indicated above, both oil pipelines and gas pipelines are susceptible to stress corrosion cracking and corrosion fatigue failures. This investigation was initiated to understand the different crack growth rate behavior of pipeline steels characteristic to the type of pressure fluctuation schemes in near-neutral pH environment, that is, oil pipelines vs. gas pipelines. It was suspected that the similar range of service life between oil pipeline steels and gas pipeline steels could be attributed to a higher rate of direct dissolution at the tip of a crack during gas pipeline operation because of much higher mean pressures, despite their lower crack growth caused by corrosion fatigue. In the case of near-neutral pH stress corrosion cracking, corrosion makes minor contribution to crack growth but produces diffusible hydrogen that interacts with cyclic loading to make cracks grow. This study was performed using specimens with surface cracks, which simulated the following two environmental conditions: 1) fully exposed to the environment, 2) shielded from the environment, exposed to hydrogen only. In Case 1), the specimen surface, on which the surface cracks were made, was fully exposed to a near-neutral pH solution, allowing the occurrence of corrosion at the crack tip. In Case 2), a narrow strip of a coating was applied to prevent the cracks from direct contact with the corrosive solution; however, the cracks were affected by diffusible hydrogen which had been generated as a by-product of corrosion on the adjacent steel surface free of coatings. These specimens were mechanically loaded under different pressure schemes typical of both oil and gas pipeline operations. It has been found that crack growth caused by direct dissolution of crack tip materials is insignificant, regardless of pipeline operating conditions. A much higher crack growth rate, attributed to hydrogen embrittlement, was found under gas transmission conditions, while a higher corrosion fatigue crack growth was found under oil transmission conditions. Based on these findings, strategies on crack growth mitigation, characteristic to each type of pipeline operation are also proposed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".