1. How to adjust the heat treatment process of alloy steel pipes according to service conditions?
High temperature service: normalizing + tempering (such as P91 steel) is used to form stable tempered martensite and improve creep strength.
Low temperature environment: quenching and tempering (quenching + high temperature tempering) is performed to ensure -46℃ impact toughness (such as ASTM A333 Gr.6).
Corrosion resistance requirements: Austenitic stainless steel requires solid solution treatment (1050℃ water quenching) to eliminate the sensitive area of carbide precipitation.
Special case: Duplex stainless steel (2205) needs to control the two-phase ratio (α/γ≈50%), which is achieved through precise temperature control annealing.
2. What are the technical challenges of alloy steel pipes in hydrogen energy transportation?
Hydrogen embrittlement risk:
Hydrogen atoms penetrate into the grain boundary and cause brittle fracture, especially affecting high-strength steel (such as X80).
Solution: Use pure steel (S/P content <50ppm) + austenitic stainless steel lining.
Sealing requirements:
Hydrogen molecules have strong permeability, requiring laser welding or special threaded connections.
Emerging materials:
Titanium alloy composite pipes and glass fiber reinforced epoxy resin pipes are being tested.
3. How to judge the quality of alloy steel pipe welds through non-destructive testing (NDT)? Comparison of the advantages and disadvantages of various methods
Applicable defect types of detection methods
Ultrasonic (UT) Internal cracks and unfused depth are quantitatively accurate, portable and require coupling agents, and have high surface requirements
Radio (RT) Porosity and slag inclusions are intuitively imaged, radiation hazards can be archived, and thick-walled pipes are time-consuming
Eddy current (ET) Surface cracks are fast, no contact is required, only conductive materials are limited, and the depth is limited
Magnetic powder (MT) Surface/near-surface defects are low cost and simple to operate, only applicable to ferromagnetic materials
Industry practice: Nuclear power pipelines usually require UT+RT dual detection.
4. What special properties are required for alloy steel pipes for deep-sea oil and gas development?
Key indicators:
External pressure resistance: The wall thickness design needs to withstand a water depth of 3000m (30MPa hydrostatic pressure).
H₂S corrosion resistance: choose super duplex steel (2507) or carbon steel + corrosion-resistant alloy lining.
Fatigue performance: considering the vortex-induced vibration of ocean currents, full-scale fatigue tests are required.
Typical materials:
Main pipe: API 5L X65MO (improved sulfur-resistant pipe).
Connectors: Inconel 625 flange.
Latest trend: Non-metallic composite pipes (such as reinforced thermoplastics) are being tested.
5. Common methods and digital progress in alloy steel pipe life assessment
Traditional methods:
Wall thickness measurement: ultrasonic fixed-point monitoring of corrosion rate.
Metallographic analysis: observe creep cavities (high-temperature pipelines) or hydrogen-induced cracks.
Hardness test: determine the degree of material aging (such as temper embrittlement).
Digital technology:
Smart pipeline: embedded fiber optic sensors to monitor strain/temperature in real time.
Big data prediction: combine historical corrosion data + AI algorithm to predict remaining life.
Digital twin: establish a three-dimensional model of the pipeline to simulate stress distribution.
Case: A petrochemical enterprise used an acoustic emission monitoring system to warn of stress corrosion crack propagation of P11 steel pipes three months in advance.
