Steel Pipe Collapse Prediction with D/t-Dependent Proof Stress
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Solution Overview
Problem
Current methods for predicting the collapse strength of steel pipes, especially large-diameter welded pipes, are inaccurate due to the use of 0.20% proof stress, which is not applicable to pipes with varying stress-strain curves, and fail to account for the influence of collapse patterns and material characteristics.
Innovation Solution
A method that uses a prediction equation relating D/t ratio, material characteristics, and collapse dominant proof stress, derived from compressive stress-strain curves, to accurately predict collapse strength by setting appropriate permanent strain values based on D/t ratios, incorporating factors like ovality, eccentricity, and residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the 0.20% proof stress is used to predict collapse strength, then the prediction is simple and can be carried out using standard material properties, but the prediction accuracy is insufficient for steel pipes with varying stress-strain curves (e.g., welded pipes with round-type or complicated SS curves)
Solution Approach 1:
The patent changes the parameter used for prediction from fixed 0.20% proof stress to a variable permanent strain value that depends on the D/t ratio. Specifically, it uses 0.05% permanent strain for D/t ≤ 19 and 0.10% permanent strain for D/t > 19. This parameter adaptation allows accurate prediction across different pipe geometries and material characteristics without requiring complex additional measurements
Solution Approach 2:
The prediction method transitions from a static approach (fixed 0.20% proof stress) to a dynamic approach where the permanent strain value is selected based on the D/t ratio of the pipe. This dynamic selection adapts the prediction criteria to match the actual collapse behavior of different pipe configurations, improving accuracy while maintaining computational simplicity
2Measurement precision
If collapse tests are performed on large-diameter steel pipes, then accurate collapse strength data can be obtained, but the testing becomes difficult or impossible to carry out
Solution Approach 1:
The patent creates a predictive model that copies the essential relationships between D/t ratio, permanent strain, and collapse strength from tested reference pipes. This model allows prediction of collapse strength for large-diameter pipes without requiring actual physical testing, effectively copying the behavior patterns observed in smaller, testable pipes to predict performance in larger, untestable pipes
Solution Approach 2:
The patent introduces a prediction equation as an intermediary between material properties and collapse strength. This equation mediates the relationship by incorporating the D/t ratio and selected permanent strain values, allowing indirect determination of collapse strength for pipes that cannot be directly tested while maintaining accuracy through the calibrated predictive model
3Adaptability or versatility
If existing prediction methods are applied to welded pipes with different stress-strain curve types, then a unified prediction approach is used, but the prediction accuracy deteriorates due to the round-type or complicated SS curves that do not exhibit clear yielding phenomena
Solution Approach 1:
The patent segments the prediction approach by D/t ratio, creating distinct prediction criteria for different geometric configurations. By dividing the prediction space into D/t ≤ 19 and D/t > 19 categories with different permanent strain values, the method adapts to the different collapse behaviors of various pipe types including welded pipes with round-type or complicated SS curves, maintaining both versatility and accuracy
Data Source
AI summary
A collapse strength prediction method of a steel pipe includes deriving a prediction equation indicating a relationship among D/t obtained by dividing an outer diameter D (mm) by a thickness t (mm), material characteristics, a collapse strength dominant factor, and a collapse dominant proof stress (σCDOS) of the steel pipe using a plurality of reference steel pipes collapse whose strengths have been obtained in advance, obtaining D/t, material characteristics, a collapse strength dominant factor, and a predicted collapse strength of a steel pipe that is an evaluation subject, obtaining a compressive stress-strain curve in a circumferential direction of the steel pipe that is the evaluation subject, obtaining a stress that causes a permanent strain to be generated in the steel pipe that is the evaluation subject as the collapse dominant proof stress on the basis of the compressive stress-strain curve, and computing the predicted collapse strength of the steel pipe that is the evaluation subject from the D/t, the material characteristics, the collapse strength dominant factor, and the collapse dominant proof stress, which have been obtained, on the basis of the prediction equation, and the permanent strain is set according to a value of the D/t of the steel pipe that is the evaluation subject.