Standards applied when periodically inspecting pressure vessels:
The process of testing pressure vessels usually applies according to the following standards:
– ASME Boiler and Pressure Vessel Code.
– National Board Inspection Code, ANSI/NB 23. API.
– QTKD 07:2016/BLDTBXH, Process of technical safety inspection of pressure vessels.
– TCVN 6156:1996, Pressure vessels. Safety technical requirements for installation, use, repair, test methods).
– TCVN 6008:2010, Pressure equipment – Welds with technical requirements and inspection methods.
Pressure vessel test cycle:
Pressure vessels must be tested for safety in the following cases:
– First inspection after installation, before putting into use.
– Periodic inspection as soon as the inspection period expires.
– After repairing, upgrading or renovating that affects the technical safety status.
– When reusing pressure vessels with downtime over 12 months.
– After changing the installation position.
– At the request of the user unit or the competent authority.
What are the requirements for periodic pressure vessel inspection?
Check records:
Consider the origin, origin and operating history of the pressure vessel. Before testing, check the following information:
– Manufacturer’s factory records (resumes, bridge drawings …)
– Operation mode
– Working environment
– Last inspection date
– Labeling specifications
– Types of weld joints in manufacturing technology
– Crafting materials
– Non-destructive inspection reports performed (thickness, weld quality …)
– Log of operation, maintenance, repair
– Record of previous inspection
To conduct technical safety testing on equipment, it is necessary to:
– Make a plan to isolate the equipment to be tested from the technology system
– Clean the surface of the device so that the outside can be checked, the inside can get accurate results
External technical inspection of the device:
External inspection to provide general information about pressure equipment condition. The inspection process shall consider the following information:
– Check the technical condition of insulation, insulation, protective paint layers.
– Check for refrigerant leaks to the outside of the paint layer, the insulation layer, etc. It is necessary to remove the coating to determine the exact cause.
– Abnormal deformations of the hanging frame, support, and working platform. Links to technology pipelines
– Check for corrosion defects, deformation on the culm, manhole, reinforcement plate. Bolts and nuts should be checked for corrosion and rust. Check flanges, gaskets…
– Check surface deformation due to mechanical impact
– Check the surface of the welds: Abnormal deformations on the surface of the weld and in the heat affected zone of the weld.
Check inside:
Only carry out an internal inspection of the pressure equipment if the fabricated metal thickness ultrasound results show unusual signs of corrosion.
Visual inspection is the first step in the process of inspecting the inside of the pressure vessel.
When inspecting the inside of a pressure vessel consider:
– All parts and surfaces inside the pressure vessel should be carefully checked to detect errors such as: corrosion, cracking, blistering, delamination, etc.
– Connections between pressure vessels and external systems
– The opening and closing doors, especially the positions subject to higher pressure than normal when the pressure vessel is under normal working conditions.
Non-destructive testing:
Non-destructive testing must be performed by experienced NDT (Non Destructive Testing) inspectors and testing equipment with specifications (sensitivity, error, measuring range, etc.) create suitable. Test results must be kept as evidence for future tests.
Commonly applied non-destructive testing methods:
– Ultrasonic inspection of fabricated metal thickness.
– Check weld defects by ultrasonic (UT), penetrant (PT), magnetic (MT) or radioactive (RT) methods.
Calculate the pressure resistance of the device:
Based on ultrasonic results of thickness and type of weld as well as stress of fabrication materials. The inspector recalculates the pressure resistance of the equipment and compares it with the results announced by the manufacturer.
Calculation results must be within the allowable endurance limits applied by the test procedure.
Pressure vessels designed and manufactured according to ASME have a factor of safety of 2.5. Pressure vessels after testing have a safety factor in the range of 2-2.5, need to be more special consideration during use. Pressure vessels with a factor of safety less than 2 should be discarded.
Pressure test
The medium commonly used during pressure testing is water. Gas termites are only allowed to be used in very special cases and there must be safety measures to ensure that no serious problems occur during implementation.
Pressure testing is performed only when there is doubt about the quality of pressure welds that cannot be evaluated by other methods or after the pressure vessel has been renovated.
The test pressure is 1.5 times the maximum allowable working pressure. The time to maintain the test pressure is not less than 5 minutes. The wall temperature of the device and the medium should not exceed 50°C (120°F).
If the vessel is under pressure to work with normal refrigerants, when the pressure drop does not exceed 10%, there is no need to test hermetically.
Processing test results of pressure vessels
– Make a record of pressure vessel inspection according to the prescribed form.
– Make minutes of recommendations and corrections (if any).
– Stamped the inspection, approved the inspection record and issued the test results of the pressure vessel.
Time limit for testing pressure vessels:
When the inspection period is specified in the national technical regulations, the provisions of that regulation shall apply.
– Period of periodic safety technical inspection is 03 years. For tanks containing corrosive, explosive and corrosive substances and used for more than 12 years, the period of periodical technical safety inspection is 02 years.
– For cylinders containing corrosive and explosive metallizers that have been used for more than 12 years and those that have been used for more than 24 years, the period for periodic technical safety inspection is 01 year.
– In case the manufacturer specifies or the establishment requires a shorter inspection time, follow the manufacturer’s regulations and the establishment’s requirements.
– When shortening the inspection period, the inspector must clearly state the reason in the inspection record.
Above is the information needed when conducting pressure vessel inspection for businesses. If you need advice on more information about boiler equipment, please contact KS Boiler for a free consultation!
KS – Boiler specializes in manufacturing, installing and maintaining industrial boilers:
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