1. Q: What are the main mechanical property requirements for SA210C grade pipe?
A: According to the ASME standard, SA210C pipe must meet minimum tensile strength of 485 MPa, a minimum yield strength of 275 MPa, and a minimum elongation of 30%-2-5. Its maximum hardness should not exceed 179 HB-5.
2. Q: What is a common metallurgical change observed in failed SA210 tubes after long-term service?
A: Studies on failed tubes show significant grain growth compared to virgin material-4. The fine ferrite-pearlite structure coarsens over time under thermal exposure and stress, weakening the material. Additionally, the formation and spheroidization of carbides and oxidation can be observed-4.
3. Q: What is one of the most common causes of failure in SA210 water-wall tubes in power plants?
A: A leading cause of failure is under-deposit corrosion (or scale-induced corrosion) on the inner wall-10. This is often directly linked to long-term poor boiler water quality, which leads to scale formation and creates localized corrosive environments beneath the deposits-10.
4. Q: Besides under-deposit corrosion, what other damage mechanism is critical for SA210 pipes in high-temperature service?
A: Creep is a critical failure mechanism. When tubes are exposed to temperatures in the range of 450–510°C for extended periods under stress, they can slowly and permanently deform, eventually leading to rupture-4. Microstructural degradation like carbide coarsening accelerates this process.
5. Q: How does the chemical composition of SA210C differ from SA210 A-1, and what is the effect?
A: The key difference is in carbon (C) and manganese (Mn) content. SA210C has a higher specified carbon range (up to 0.35% vs. 0.27% for A-1) and a higher manganese range-5-7. This composition gives SA210C its higher tensile and yield strength compared to the A-1 grade-2.
