Manufacturing, inspection, and acceptance of pressure vessels

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Manufacturing, Inspection, and Acceptance of Pressure Vessels I. Characteristics of Pressure Vessel Manufacturing 1. Different components (shape, material) are manufactured separately and then assembled； The main assembly method is welding. 2. Multiple cold and hot processing methods are required, among which hot processing technology and quality are crucial (due to the diversity of factors affecting quality and the difficulty of inspection) ； 3. It relates to safety; it is a quality inspection rather than a performance test, therefore full-process quality control is required. II. The Importance of Structural Design (Selection) 1. The structure is the key factor determining safety and cost-effectiveness ； Structure is the foundation of computation ； Attention should be paid to correcting the tendency to prioritize computation over simplicity in structure design ； 2. Basic requirements for structural design: Suitability (meeting usage requirements) ； Safety ； Economy. The three are often contradictory, and good design lies in achieving a dialectical unity. 3. Several Examples of Structural Design 3.1 Butt joints with unequal thicknesses 3.2 Radius transitions and chamfers 3.3 Even distribution of flange bolt holes at the mid-span 3.4 Requirements for foot bolt holes 3.5 Welded structures a. Basic requirements for welded structure design: ease of welding and inspection ； Reduce welding workload ； Ensure full penetration ； b. Design characteristics of welded structures: Closely related to workers’ skills and practices; it is not a mandatory requirement. 3.6 Thoughts on Structural Design Abroad a. Number of manholes in spherical tanks b. Installation of safety valves on tank trucks III. Welding 1. Differences between welded joints and base metal 2. Elements affecting welding quality and corresponding countermeasures 2.1 Mechanical properties – Welding procedure qualification, product welding test plates 2.2 Welding defects – Non-destructive testing 2.3 Visual quality – Macroscopic inspection 3. Mechanical properties 3.1 Welding procedure qualification a. Purpose – Prevention and guidance in advance ； Cost savings b. Practices and requirements for evaluation 3.2 Product welding test plates a. Purpose – post-inspection b. Preparation conditions and quantity c. Preparation requirements – representativeness d. Inspection – JB47444, welding defects 4.1 Types of defects 4.2 Undercutting a. Causes and hazards of undercutting ； b. Inspection for burrs — macroscopic inspection ； c. Requirements for burrs per standards 5. Appearance quality 5.1 Misalignment a. Causes and prevention of misalignment: Class A joints – alignment required ； Class B joint – outer circumference ； Locally irregular in shape. b. Hazards of misalignment: reduced thickness ； Shape mutation. c. Measurement of misalignment: generally the outer wall ； Inner wall of composite panel. 5.2 Sharp corners a. Causes and prevention of sharp corners – welding deformation b. Hazards of sharp corners 5.3 Weld bead height a. Function of weld bead height b. Hazards of weld bead height c. Requirements for weld bead height according to standards 6. Main differences in product quality between China and other countries – appearance quality IV. Heat treatment 1. Classification of heat treatment by purpose 1.1 Post-welding (stress relief) heat treatment a. Purpose b. Causes, characteristics, and hazards of welding stress c. Conditions for post-welding heat treatment – general conditions: thickness, material, and preheating temperature ； Special conditions—Stress corrosion indicated on the drawing ； For containing highly toxic and extremely dangerous substances ； Condition not required—Austenitic stainless steel.    1.2 Heat treatment for restoring mechanical properties a. Causes and hazards of cold working hardening b. Conditions for heat treatment at low and medium temperatures c. Heat treatment of cold-formed heads (except austenitic stainless steels) 1.3 Heat treatment to improve the mechanical properties of materials 1.4 Dehydrogenation treatment 2. Post-welding heat treatment methods —— in a furnace as a whole ； in segmented furnace ； local ； On-site 3: Advanced post-weld heat treatment process, temperature upon exiting the furnace ； Rising and falling temperature rates ； Furnace atmosphere ； Extracorporeal cooling V. Non-destructive testing 1. Characteristics and selection of different methods 1.1 Characteristics of radiography, ultrasonic testing, magnetic particle testing, and penetrant testing 1.2 It is the responsibility of the designer to choose the appropriate method 1.3 Factors to consider when making a choice a. Material ； b. Structure ； c. Thickness ； d. Method 2: Selection of non-destructive testing lengths for weld joints of categories A and B 2.1 Conditions for 100% radiographic or ultrasonic testing a. Thickness (P, D) – safety, importance, cost efficiency b. Material – weldability, different effects of the same defect on various materials, importance, cost efficiency c. Safety requirements of the product – severity of potential accident consequences d. Special characteristics of the structure 2.2 Local radiographic and ultrasonic testing a. Meaning and purpose of local testing b. Areas in the product that require 100% testing (openings, covered joints, seams of convex heads, embedded fittings, fittings with D ≥ 250 mm). 3. Correct understanding and implementation of local inspection; requirements for manufacturers and users. 4. Re-inspection using different methods. 5. Requirements for non-destructive testing as stipulated by designers. VI. Pressure resistance and airtightness tests 1. Pressure resistance test 1.1 Purpose: a. Internal pressure – to assess strength and detect leaks ； b. External pressure (vacuum) — leak detection. 1.2 Differences in the hazards of hydraulic and pneumatic systems a. Hydraulic systems ~ Energy (P×V), metal fragments ； b. Air pressure~energy (P×V), metal fragments, shock waves. 1.3 Conditions permitting air pressure a. Unable to use hydraulics due to load-bearing constraints ； b. The liquid must be completely drained and dried; residual liquid is not allowed during production. 2. Airtightness test 2.1 Purpose — Detecting leaks 2.2 Conditions requiring an airtightness test a. Toxic substances must not leak ； b. The production process does not allow leaks. 2.3 The test pressure depends on the medium. 2.4 Whether airtightness testing is still necessary after the air pressure meets the requirements also depends on the medium. 2.5 Leak detection methods and acceptance criteria – Professional information sharing