Understanding Type A and Type B Repairs Under ASME PCC-2

Composite repairs have become a go-to solution for reinforcing the structural integrity of pipes and vessels while also serving as a protective barrier against corrosion. However, the success of these repairs depends on a clear understanding of the differences between external and internal wall loss repairs. ASME PCC-2 outlines two main design cases for corrosion: Type A and Type B. The calculations involved in each type can vary significantly, and using the wrong one can lead to ineffective or even failed repairs. **Type A vs. Type B Repairs** Type A repairs are intended for non-leaking components that maintain a minimum wall thickness of 0.04 inches throughout the life of the repair. These repairs are typically used for pipes with localized corrosion that hasn’t yet caused a leak or through-wall damage. The primary goal here is to restore the structure, and the composite material helps prevent further external corrosion. On the other hand, Type B repairs are designed for leaking components or those with less than 0.04 inches of wall thickness at any point during service. If a component has been stop-gapped due to a leak, it should be classified as a Type B repair. Internal corrosion is usually treated as a Type B case unless the corrosion rate indicates that the remaining wall thickness will stay above 0.04 inches. Unlike Type A repairs, Type B requires sealing the through-wall defect in addition to structural reinforcement. This makes proper surface preparation and adhesion essential for long-term performance. **Understanding Type B Repair Design Categories** Type B repairs are divided into three categories based on the nature of the defect: - **Circular or near-circular defects:** These involve localized through-wall damage or internal corrosion where full wall loss hasn't occurred yet. - **Circumferential slot defects:** These occur when there's a long section of full wall loss around the entire circumference of the pipe, often due to clamps or patches used to stop leaks. - **Axial slot defects:** These are found in long sections of full wall loss that are isolated to one side of the pipe, such as corrosion on the bottom. Although ASME PCC-2 doesn't specify pressure limits for Type B repairs, pressure must still be considered in the calculation process. It’s generally recommended to use a maximum pressure limit of 500 psi when designing composite repairs for Type B cases. **Aligning Design Calculations with the Repair** One common mistake is when the design calculations don’t match the actual defect. For a Type B repair, you need both Type A structural reinforcement calculations and Type B defect-specific calculations. Type A may suggest fewer layers, but without proper integration, this could lead to an under-designed repair that fails over time. It’s crucial to review the design package thoroughly. Ask yourself: - Is the engineering assessment accurate? - Do the calculations reflect the actual defect on the pipe? - Are the correct equations being used for the specific repair? **Addressing Corrosion for a Type B Repair** In a recent project, an operator faced a corroded pipe classified as a Type B repair due to deep external corrosion from corrosion under insulation (CUI). The defect was presented as a circumferential slot because of the band and patch used to stop an active leak. To ensure a successful repair, the entire patched area had to be treated as a defect. Navigating the complexities of ASME PCC-2 repairs requires a solid grasp of the distinctions between Type A and Type B repairs. Misalignment between calculations and the actual defect can result in ineffective repairs and long-term failure. Always double-check your design packages and ensure they align with your specific needs. HJ3 understands the nuances between Type A and Type B repairs and can help you develop tailored solutions. Contact us today to learn more about how we can support your repair projects.

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The terminal amino group of Nylon 6 slice refers to the content of -NH3 group in the macromolecular chain. The number-average molecular weight of the slice can be calculated by the content of the terminal amino group, and the method of blocking the terminal group of the polymer, the antioxidant capacity and the speed of dyeing can be speculated.

The amino group content of Nylon 6 Chips is generally controlled at about 40. The higher the content, the higher the dyeing rate of the spun Nylon 6 Yarn, the faster the dyeing, and the deeper the dyeing color. The amino acid content of the nylon 6 slices used for spinning should be controlled at a high level, but too high is not good for the uniformity of dyeing. It is more beneficial to control the low content of terminal amino groups in shallow colors.

The amino-terminal content of nylon 6 slices should be determined according to the requirements of customers. Only a few companies such as Haiyang Technology are able to provide customized services in the market. More importantly, the amino-terminal content of Haiyang Qiuxue nylon 6 slices The content is stable, which is critical for the uniformity of spinning and dyeing of silk sources.

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