To conduct a review, safe technical inspection according to the following steps:
- To prepare the testing: Item 3.1
- To check dossier: Item 3.2
- To check outside: Item 3.3
- To check inside: Item 3.4
- To check the capability to bear pressure: Item 3.5
- To check the tightness, only apply to the vessels working with toxic and flammable solvent-substance: Item 3.6
- To check the operation: Item 3.7
Note: The following inspections are conducted only when the inspection results of the previous step has been satisfactory.
Before conducting the search: The safety measures must be taken, pressure vessels must be cleansed; the inspection door, door for person to creep into (if any) must be removed; when having doubt on technical state of the parts bearing pressure of the vessel, it need to be removed a part or the whole of the insulation layer to ensure to the external, internal examination; the establishment must appoint a person to witness the search.
3.1. Preparation of testing
3.1.1. To notify the establishment of the plans and requirements before implementing the testing of vessels.
3.1.2. To define and agree on the safety measures with the establishment before implementing the testing. To prepare fully the instruments, facilities, checking equipment used for the testing process.
3.2. Inspection of dossier
3.2.1. Based on the testing regime to inspect and review dossier of vessel.
3.2.1.1 When testing the first time, it must consider the following records:
a, Profile of vessel (including the norms of fabrication metal, welding metal, strength calculations of pressure elements; drawing of structure written fully the main size and guidance of the operation, maintenance and repair …).
b, Factory profile of vessels (including certificates of fabrication metal, weld metal, testing results of weld quality; minutes of trial …).
c, The minutes of the testing of mesurement unit; The minutes of checking ground, anti-lightning, protection device (if any).
d, Profile of installation: only applies to the fixed vessel
3.2.1.2 When testing periodically, it must review the following documents:
a, History, testing minutes and the results of previous testing.
b, Records on the management and use, operation and maintenance; minutes of inspection, testing (if any).
3.2.1.3 When testing irregularly, it must review the following documents:
a, In case of repair: repair design dossiers, minute of acceptance testing after repair with weld and replacement of parts under pressure.
b, In case of changing the location of installation: it needs to be considered to supplement the installation dossier.
c, If, after testing, equipment does not work from 12 months or more, it shall be reviewed dossier as for periodical testing.
Note: For the pressure vessels having clear origin, but the technical dossier is incomplete, then it must be supplemented.
3.3. Outside and inside inspection
The outside and inside inspection is implemented according to the order of steps as follows:
3.3.1. When searching the indise and outside of the pressure vessels, the following lacks need to be paid attention to detect:
- The inside and outside cracked, sunken, bloated marks of the pressure vessel; gas leak trace at the weld, rivet connection, pipestopper.
- Status of sediment, rust, corrosion of metal parts.
- Technical status of the accessories, tesing and measurement tools and safety.
- Technical status of the insulation layer.
- To check the tightness of the connection details.
- For the location that is unable to carry out the inside search when testing, the inspection of technical conditions must comply withthe technical documentation of the manufacturers. It must be written clearly in the documents: the amount needs to be inspected,methods and order of inspection.
3.3.2. To check the location of installation of equipment: lighting system; floors, stairs, racks ... anti-lightening, ground system (if any).
3.3.3. To check the number and working situation of the accessories.
3.3.4. For vessels that work with the toxic, flammable substance, it must take measures to remove air prior to the inspection; the persons who direct examine must know clearly the process of common troubleshooting.
3.3.5. If the vessel has shell-and-tube, if having doubt on the technical state in the shell-and-tube zone, it must be requested to remove each part or the whole shell-and-tube.
Note: If it is unable to conduct the inside search due to the structural characteristics of the vessel, it is permitted to replace the inside search by hydraulic test with the prescribed testing pressure and examine the parts that are able to conduct.
3.5. Inspection of the capability to bear pressure (hydraulic test)
The hydraulic test aims to test the durability and tightness of vessels.
3.5.1. If the vessel has the structure of many parts working at the level with different pressures that may be separated and hydraulictest for each part
3.5.2. It must take measures to restrain the effects of the course of hydraulic test to the automatic protection equipment, testing and measurement equipment and make sure the devices not be destroyed during the course of testing. In case of unable to implement, it must be isolated or removed for separate testing.
3.5.3. Solvent-substance and temperature of testing solvent-substance, testing pressure, time to maintain pressure as prescribed in the item 3.11 of TCVN 6156:1996 if the manufacturer has defined higher testing-pressure, it shall be in accordance with provisions of the manufacturer.
3.5.4. Where there is no conditions for hydraulic test due to the expansion on the nail bed, floor or difficulties in drainage; due to theinner base coat preventing water, it is permitted to replace by gas pressure testing (air or inert gas) and conduct the inspection of the tightness with soap solution or by other means, in the process of testing, it must apply the safety measures prescribed in 3.16 TCVN 6156:1996.
3.5.5. Using reagents and conducting the slow increase of pressure to avoid sudden dilatation causing damages for the devices to maintain the testing pressure within 5 minutes and prohibit the use of hammer. Monitoring, detecting the phenomenon: deformation, cracks ... during the hydraulic test.
3.5.6. Decreasing pressure slowly back to the standard pressure, keeping it during the course of searching. Using hamber for checking at the location that has been doubt, then decreasing pressure back to (0); recovering the exist (if any) and rechecking the results that have been recovered.
3.5.7. Valuating the testing result: It must satisfy the results at least as prescribed in item 3.4.5 TCVN 6154:1996.
3.5.8. In case vessels are exempted from hydraulic test in accordance with provisions of TCVN on current safe technique, it must be written clearly in the testing minute and attached to the hydraulic acceptance test minutes of manufacturer, installation acceptance test minute (if any).
3.6. Inspection of tightness (closed test): It is applied only when required by technology or the vessels working with toxic andflammable solvent- substance.
3.6.1. Using reagents being inert gas or compressed gas to refill to the permitted working pressure.
3.6.2. Detecting the leaks; proposing the measures for the establishment to recover, handle and re-check.
3.6.3. Valuating the testing result: vessels are considered as satisfactory at this testing when gas leak is not detected.
3.7. Operating inspection (operating test).
3.7.1. To check fully conditions enabling the vessels to operate normally.
3.7.2. Based on the process, coordinate with the establishment sending vessel for using; consider the normal working condition of vessels and accessories; the work of measuring, protective devices.
3.7.3. When the vessels work stably, the increase of pressure for checking and the adjustment of working pressure of the safe valve, the lead seal for the safe valve shall be implemented (except for the vessels containing the toxic, flamable solvent-substance).
The safe valve may be adjusted and sealed lead not at the same of the process of operation.
Adjustment value of the safe valve:
+ 0,05 MPa – When the working pressure allowed up to 0,3 MPa;
+ 15% p - When the working pressure allowed more than 0,3 MPa to 6 MPa;
+ 10% p - When the working pressure allowed more than 6 MPa.