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The document for the occupational safety training course on operating pressure equipment helps workers equip themselves with safety knowledge and prevent hazards when working with pneumatic, high-pressure equipment.

Table of Contents

PART 1: PRESSURE EQUIPMENT SAFETY IN THE SAFETY DOCUMENT FOR OPERATING PRESSURE EQUIPMENT

I. GENERAL INTRODUCTION

Incidents that occur during the operation of pressure equipment are always accompanied by accidents causing serious injury and death. Each year, hundreds of serious incidents involving pressure equipment occur, causing severe injuries and dozens of fatalities. Within the scope of this article, we will present some measures to minimize risks when working with pressure equipment that are not portable gas cylinders or tanks. Safety measures for portable gas cylinders and tanks will be covered in another article.

Pressure equipment is understood as any system or device that works with liquid or gas at a pressure higher than atmospheric pressure.

The main hazards associated with pressure equipment:

The equipment can rupture, causing impact and a blast wave that exerts pressure on people and nearby equipment.
The medium inside the system can be released due to rupture or leakage, causing burns and poisoning to people.
Flammable substances, when released, can cause fires.

The basic causes of incidents involving pressure vessels include:

Equipment designed incorrectly for the working conditions.
Improper installation. Incorrect repair or modification procedures.
Poor maintenance conditions.
Incorrect operation due to the operator not being adequately trained, supervised, or reminded.

The risks associated with pressure equipment depend on the following factors:

The pressure inside the system. The type of medium contained within the system and its properties.
The quality of the equipment’s design, manufacturing, and installation.
The operating time and working conditions of the equipment.
The complexity of the operating procedure.
The severity of the operating conditions (e.g., high or low temperatures, abrasive or corrosive media, cracking, etc.).
The skill level and understanding of the people who design, manufacture, install, maintain, test, and operate the pressure equipment system.

II. RISK MITIGATION MEASURES IN THE SAFETY DOCUMENT FOR OPERATING PRESSURE EQUIPMENT

1. Safety must be a concern from the moment of ordering and purchasing equipment

When installing new equipment, it must be ensured that the equipment is designed appropriately for the conditions of use and fully complies with the regulations in current safety standards (TCVN 6153: 1996 to TCVN 6156: 1996 for pressure vessels, TCVN 6004:1995 to TCVN 6007: 1995 for boilers, TCVN 6008:1995 for the quality of pressure equipment welds, TCVN 6413:1998 for fire-tube boilers, TCVN 6104:1996 for refrigeration systems, TCVN 6486:1999 for LPG tanks, TCVN 6158:1996 and TCVN 6159:1996 for steam and hot water pipelines, etc.). However, it should be noted that the aforementioned standards often only provide very basic requirements; detailed design usually has to rely on foreign design standards such as ASME, TEMA, BS, DIN, JIS, etc., while ensuring compliance with the requirements of Vietnamese standards.
The equipment must be manufactured from materials suitable for the medium and working conditions.
The technological process must be chosen so that the operation has the least impact on the equipment (e.g., no need to climb on the equipment, no need to tap or hit the equipment, etc.).
Be extremely careful when repairing or modifying pressure equipment. Repairs and modifications must follow strictly and detailed technical plans and be carried out by individuals or units with full capacity and legal status. The repair and modification process must be closely supervised. The equipment must be fully inspected and tested after modification or repair.

2. Managers, operators, and maintenance personnel must fully understand the equipment’s operating conditions

Understand the type of medium being stored, processed, and transported inside the equipment and its characteristics (e.g., toxicity, flammability, etc.).
Understand the operating conditions of the equipment, such as pressure, temperature, abrasion, corrosion conditions, etc.
Understand the parameter limits for the safe operating range of the equipment as well as all other directly related or directly affected equipment.
Detailed operating and incident handling instructions must be prepared for each part as well as for the entire equipment system.
Ensure that operators, repair personnel, and all other relevant individuals have been thoroughly instructed, trained, and tested on the operating and incident handling procedures (see the section on training below).

3. All protective devices must be installed and ensured to be always in a ready-to-work state

Protective devices such as safety valves, pressure relays, as well as other protective devices intended to shut down the equipment when the pressure, temperature, or level of the medium inside the equipment exceeds the permissible level must be fully installed on the pressure vessel and piping system.
Protective devices must be calibrated and set at appropriate activation parameters.
If there are alarm devices, they must be installed so that their sound and light signals are most easily noticeable.
Ensure that protective devices are always in perfect condition, ready to operate.
Automatic discharge devices such as safety valves and rupture discs must have discharge pipes leading to a safe location.
Ensure that only responsible and authorized personnel are allowed to change the setting parameters of the protective devices.

4. Fully implement the equipment maintenance process

Each production unit must establish a maintenance plan for the entire system of pressure equipment in the unit. The maintenance plan must take into account the specific characteristics of each piece of equipment, such as its lifespan, operating characteristics, working environment, etc.
Always pay attention to unusual signs in the system, for example: if the safety valve frequently activates, it means the system is abnormally over-pressurized or the safety valve is faulty – Always check for signs of wear and corrosion.
Before performing maintenance or repairs, ensure that all pressure inside the system is released and the system is thoroughly cleaned.
All safety measures and procedures must be fully implemented during repair and maintenance.

5. Fully implement the training and instruction process

All operators, maintenance personnel, repairers, and others involved with pressure equipment, especially new workers, must be adequately trained and instructed.
Training must be repeated in the following cases: When changing jobs. When the equipment or operating procedure changes. After a period of not working or changing to a different job. After each annual interval.

6. Equipment must be fully registered and inspected

According to current regulations, all of the following equipment:
- Pressure vessels with a working pressure greater than 0.7 kG/cm², volume greater than 25 liters,
- Boilers with a working pressure greater than 25 liters, hot water heaters with a water temperature greater than 115°C.
- Saturated steam pipelines with a diameter of 76 mm or more, superheated steam pipelines with a diameter of 51 mm or more.
- Gas pipelines must be safety inspected by inspection centers and registered for use with the local Departments of Labor, Invalids and Social Affairs before being put into use, and must be periodically inspected by inspection units during use. The procedure for inspection is stated in Circular No. 04/2008/TTBLDTBXH dated February 27, 2008, of the Ministry of Labor, Invalids and Social Affairs.
The inspection period specified in the technical safety standards varies for each type of equipment, but generally includes the following intervals:
- Every 3 years for internal and external examination, every 6 years for an examination accompanied by a hydrostatic test for pressure vessels.
- Every 2 years for internal and external examination, every 6 years for an examination accompanied by a hydrostatic test for boilers.
- For refrigeration systems, the inspection cycle is every 5 years for an examination accompanied by a strength test; during this 5-year period, an examination will be conducted 3 years after the test. A 2000-liter, 10kg/cm² pressure compressed air tank, model BKN 2-10, is used to accumulate pressure for other pneumatic machines.

III. DUTIES OF THE OPERATOR

Regularly check the condition of the tank, the operation of the inspection and measurement instruments, the safety mechanisms, and the fittings of the tank. Regularly check the condition and safety mechanisms of the machines related to the compressed air tank, which are the PVMA air compressor and the plate cutting machine (or other pneumatic machine). Regularly check the dust filter and oil level of the air compressor.
Operate the tank safely according to the correct procedure. Promptly and calmly handle incidents according to the correct procedure, and immediately report any unsafe phenomena of the tank to the person in charge.
While the tank is in operation, do not engage in personal activities or leave the workstation.

IV. OPERATING PROCEDURE

Check according to the regulation at point 1, section A. Open the bottom drain valve to discharge condensate, then close the valve.
Operate the air compressor to supply air to the tank. When starting the compressor for the first time in a day, the air must be vented until P=0, then start. During operation, the compressor may only be restarted when P < 2 KG/cm².
Open the air inlet valve to slowly supply air to the compressed air tank at a pressure less than or equal to the working pressure (P ≤ 8KG/cm²).
Open the gas supply valve to the load (on the gas outlet line) to supply compressed air to the plate cutting machine (or other pneumatic machine).
When the work is completed, stop the air supply to the tank, turn off the machine, close the valves, and disconnect the power supply to the machine.
If a gas leak or an incident is detected, immediately stop the air supply to the compressor tank and gradually reduce the tank’s pressure by venting through the safety valve; immediately report to the person in charge for inspection and handling.

PART 2: SAFE OPERATION OF AIR COMPRESSOR TANKS

A 2000-liter, 10kg/cm² compressed air tank, model BKN 2-10, is used to accumulate pressure for other pneumatic machines.

I. DUTIES OF THE OPERATOR

Regularly check the condition of the tank, the operation of the inspection and measurement instruments, the safety mechanisms, and the fittings of the tank. Regularly check the condition and safety mechanisms of the machines related to the compressed air tank, which are the PVMA air compressor and the plate cutting machine (or other pneumatic machine). Regularly check the dust filter and oil level of the air compressor.
Operate the tank safely according to the correct procedure. Promptly and calmly handle incidents according to the correct procedure, and immediately report any unsafe phenomena of the tank to the person in charge.
While the tank is in operation, do not engage in personal activities or leave the workstation.

II. OPERATING PROCEDURE

Check according to the regulation at point 1, section A. Open the bottom drain valve to discharge condensate, then close the valve.
Operate the air compressor to supply air to the tank. When starting the compressor for the first time in a day, the air must be vented until P=0, then start. During operation, the compressor may only be restarted when P < 2 KG/cm².
Open the air inlet valve to slowly supply air to the compressed air tank at a pressure less than or equal to the working pressure (P ≤ 8KG/cm²).
Open the gas supply valve to the load (on the gas outlet line) to supply compressed air to the plate cutting machine (or other pneumatic machine).
When the work is completed, stop the air supply to the tank, turn off the machine, close the valves, and disconnect the power supply to the machine.
If a gas leak or an incident is detected, immediately stop the air supply to the compressor tank and gradually reduce the tank’s pressure by venting through the safety valve; immediately report to the person in charge for inspection and handling.

PART 3: STRUCTURE AND OPERATION OF A DOUBLE-JACKETED COOKING POT

I. GENERAL STRUCTURE

Rice cookers, soup pots, and woks that use saturated steam for heating are generally double-jacketed pots. The food is placed in the inner pot, and steam is supplied to the space between the two jackets. The outside of the pot is covered with a layer of insulating glass wool, and the outermost layer is stainless steel. The pot is cold tested at a pressure of 5 atm, and it is recommended to work with a pressure of 2 ~ 2.5 atm. The pot is equipped with the following accessories:

01 Pressure gauge to monitor the pot’s pressure
01 Spring-type safety valve to control the pot’s pressure, keeping it within the permissible limit
A bottom drain valve assembly including 01 branch valve and 01 integrated cup drain valve to discharge condensate from the pot during operation.

II. OPERATING THE COOKING POT IN THE SAFETY DOCUMENT FOR OPERATING PRESSURE EQUIPMENT

Put the food into the pot
Slowly open the steam valve all the way to maintain the pressure in the cooking pot at 2.5 atm. If the pressure exceeds 2.5 atm, the safety valve will open (release steam); in this case, turn the steam valve down to maintain the cooking pressure.
Open the branch valve in the drain assembly for about 1 minute to completely discharge the condensate in the pot, then close the valve tightly.
When cooking food, maintain a cooking pressure of 2.5 atm until the food is cooked. * When cooking rice – Pour enough water into the pot to cook the rice (based on experience with the type of rice).
Open the steam supply valve, bring the water in the pot to a boil, then add the rice to the pot and cover it.
When the rice boils, stir it evenly until the water is absorbed.
When cooking rice, you must maintain a pressure of 2~2.5 atm until the water is absorbed, then partially close the steam valve to maintain a cooking pressure of 1.5 atm until the rice is cooked.

Throughout the rice cooking process, if the indicated pressure is greater than 2.5 atm, the safety valve will pop and release steam. You need to partially close the steam supply valve (if necessary, you can close it for a while). Only when the pressure gauge shows the pressure has dropped below 2 atm should you gradually open the steam supply valve again.

After cooking is finished, close the steam valve. If you need to cool the pot quickly for cleaning, open the branch valve in the drain assembly to release all the steam from the pot.

III. COMMON MALFUNCTIONS IN THE SAFETY DOCUMENT FOR OPERATING PRESSURE EQUIPMENT

The pot heats poorly (not enough cooking temperature), which may be due to two reasons:
- The steam source is not supplying the required steam pressure. To fix this, request the boiler side to increase the steam supply.
- There is too much condensed water in the steam-containing part of the cooking pot. To fix this, open the branch valve in the drain assembly to thoroughly discharge the condensate. If, after handling the branch valve and closing it, the poor heating occurs again after a while (even though the pressure is still as required), the drain assembly may be clogged. In that case, the drain valve assembly needs to be disassembled for cleaning and flushing out debris.
Steam leaks from the shaft end, or a union joint, or a valve stem… The operator needs to inform the on-duty electromechanical technician to tighten the bolts, compress the packing, or add packing to the leaking points.

IV. TECHNICAL SAFETY MEASURES WHEN OPERATING THE COOKING POT

The operator must wear all issued personal protective equipment.
The operator must follow the pot’s operating procedure they have been taught.
Do not arbitrarily adjust or break the seal of the safety valve. During a shift, the operation of the safety valve must be checked at least once (by using 7 hands to pull the valve’s lever; if steam is released and it closes tightly when released, the safety valve is working normally).
Do not operate the cooking pot if one of the two accessories, the safety valve or the pressure gauge, is missing or damaged.
Immediately stop operating the cooking pot if a crack is found on the inner body of the pot or if steam is leaking from the outer shell through the insulation layer:
- Report to the direct supervisor for handling measures.
- Hand over to the next shift.
Safety requirements for using pressure vessels
1. Pressure vessels (hereinafter referred to as vessels, including electric boilers, tanks, and containers) must be inspected, registered, and issued an operating permit in accordance with current regulations before being put into use.
2. The application for registration includes: A logbook, original or transfer documents, installation records (for fixed vessels), a structural drawing of the vessel with main dimensions, an application for a permit, and other documents as required by current regulations.
3. Vessels that have been modified, restored, installed in a new location, or have a change of owner must also be re-registered.
4. On each vessel, after registration, a painted frame of 150 x 200 (mm) must be marked in a clearly visible place, containing the following data: Registration number; permissible working pressure, date of inspection, and next inspection date.
5. The owner of the vessel must fulfill the following requirements:
  - Assign responsibility in writing to the vessel user;
  - Issue an operating procedure for the vessel;
  - Organize periodic safety technical training for users;
  - Establish a system for checking the metal condition of parts working at temperatures of 450°C or higher;
  - Ensure that technical inspections are carried out on schedule.
6. The vessel room must have a clock and a means of communication with the vessel owner.
7. Unauthorized personnel not involved in the management or operation of the vessel are not allowed to enter the vessel area or the storage area for filled gas cylinders.
8. The user of the vessel must ensure:
  - Proper maintenance and operation according to procedure;
  - Timely repairs and preparation of all necessary conditions for technical inspections;
  - Promptly rectify any faults during operation.
9. The operation of vessels shall only be entrusted to persons who are 18 years of age or older, in good health as required, and have been trained and tested on professional knowledge, procedures, and safety technical regulations and have met the requirements.
10. The direct user of the vessel has the following main duties:
  - Regularly check the condition of the vessel, the operation of the inspection and measurement instruments, the safety mechanisms, and the fittings of the vessel;
  - Operate safely according to the unit’s procedure; promptly and calmly handle incidents according to the unit’s procedure, and immediately report any unsafe phenomena of the vessel to the person in charge;
  - While the vessel is in operation, do not engage in personal activities or leave the workstation.
11. The owner and user of the vessel must not operate the vessel beyond the specified parameters. It is forbidden to jam, block, or use any means to increase the load on the safety valve while the vessel is in operation.
12. The owner and user of the vessel must immediately stop the operation of the vessel in the following cases:
  - When the working pressure exceeds the permissible level, even if other requirements specified in the vessel’s operating procedure are met;
  - When the safety mechanisms are not functioning perfectly;
  - When cracks, bulges, steam leaks, or water leaks are detected in the basic components of the vessel, at welds, or when gaskets are torn;
  - When a fire directly threatens the pressurized vessel;
  - When the pressure gauge is damaged and it is not possible to determine the pressure in the vessel by any other means;
  - When the sight glass is damaged;
  - Other cases as specified in the unit’s operating procedure.
13. Storage and transportation of tanks and containers:
  - The procedures for storing and transporting tanks or containers of liquefied gas, as well as the procedure for evacuating gas from tanks and containers, must be specified in the procedures of the relevant units;
  - Tanks filled with liquefied gas transported by rail, as well as containers of liquefied gas carried on a train deck, must comply with the regulations for the transport of heavy bulk materials by rail;
  - When transporting or handling containers of liquefied gas, measures must be taken to prevent them from falling, toppling, being exposed to direct sunlight, and from localized heating.
14. Storage, use, and transportation of gas cylinders:
  - When it is necessary to transfer gas from a cylinder with a higher pressure to a cylinder with a lower working pressure, it must be done through a pressure-reducing valve specific to each type of gas. The low-pressure side of the pressure-reducing valve must have a pressure gauge and a safety valve that has been adjusted to match the working pressure of the receiving cylinder.
  - For cylinders containing highly corrosive gases such as chlorine, sulfur dioxide, phosgene, etc., if it is not possible to use a pressure-reducing valve, another reliable method may be used with the approval of the competent authority.
15. In case the cylinder valve is damaged and the gas cannot be released, or for cylinders that have not been used for a long time and the internal gas pressure cannot be determined, or for cylinders with damaged bases or necks, etc., they must all be returned to the gas filling plant for handling. Before reusing old gas cylinders for different purposes, if the valve is stuck, the valve must also be removed, the gas released, and degassing measures applied as necessary by the gas filling plant.
16. Gas cylinders must be placed at least 5m away from any open flame; and not less than 1.5m away from electric heaters and other heating devices.
17. When storing filled gas cylinders, they must be placed in an upright position in racks to prevent them from falling. Cylinders without bases must be stored in a horizontal position. For temporary outdoor storage, cylinders may be stacked horizontally in piles, but rope, wooden planks, or rubber must be placed between the layers. The height of the stack must not exceed 1.5m, and all valves must face the same direction.
18. The movement of cylinders in the gas filling plant or at the point of consumption must be carried out using specialized small carts or other safe methods. The service personnel must be trained in professional skills appropriate for each task.
19. Filled gas cylinders must be transported using vehicles with springs. The cylinders must be placed horizontally, with all valves facing the same direction. Padding made of rope, wooden planks with holes, or rubber rings with a thickness of 25mm or more must be placed between the layers of cylinders. Each layer of cylinders must be padded in at least two places. It is permissible to transport cylinders in an upright position using specialized vehicles, but there must be padding between the cylinders and a barrier to prevent them from falling or tipping over. Standard cylinders with a capacity of more than 12 liters must have caps covering the valves during transport and storage.
20. When transporting filled gas cylinders by road, the person in charge of the vehicle must comply with the following requirements:
  - It is forbidden to mix cylinders with oil, grease, and other flammable materials; – It is forbidden to transport people with cylinders;
  - It is forbidden to park the vehicle in direct sunlight, in crowded places, or on busy streets. During transport and handling of cylinders, measures must be taken to prevent them from falling or tipping over.
21. The transport of filled gas cylinders by rail, water, or air must comply with the regulations of the respective transport authorities.
22. It is forbidden to transport filled gas cylinders by animal-drawn vehicles.

V. APPLICATIONS

Air compressors are used to supply high-pressure air to industrial machine systems to operate them, to start large-capacity engines, to run pneumatic motors, or machinery and equipment in many other specialized fields…

PART 4: TYPES OF AIR COMPRESSORS BY OPERATING MECHANISM

1. Rotary Screw Compressor in the Safety Document for Operating Pressure Equipment

A rotary screw compressor uses the rotary motion of two intermeshing helical screws to force gas into a smaller volume. They are widely used for continuous operation in both commercial and industrial applications and can be stationary or portable. Their capacity can range from 5 to over 500 HP, from low to very high pressure (8.3 MPa).
This type is used to supply compressed air to many types of machine tools. They can also be used for engines with superchargers, such as in cars or airplanes.

2. Reciprocating Compressor

A reciprocating compressor uses a piston driven by a crankshaft. It can be stationary or portable, and can be used individually or in combination. They can be driven by an electric motor or an internal combustion engine.
Small reciprocating compressors with a capacity of 5-30 horsepower are often used in automated assembly and in non-continuous applications.
Large compressors can have a capacity of up to 1000 horsepower and are used in large industrial assembly, but they are not commonly used as they can be replaced by rotary screw compressors at a lower cost. The output pressure can range from low to very high (>5000 psi or 35 MPa).

3. Axial Compressor in the Safety Document for Operating Pressure Equipment

An axial compressor uses a series of rotating blades (rotors) to compress the gas flow. Fixed stator blades located downstream of each rotor direct the gas flow into the next set of rotor blades. The area of the air passage gradually decreases through the compressor to increase the compression. Axial compressors are often used when a high flow rate is needed, such as in large turbine engines. They are almost always used in a multi-stage configuration. For pressure ratios below 4:1, variable geometry is often used to improve operating efficiency.

4. Centrifugal Compressor in the Safety Document for Operating Pressure Equipment

A centrifugal compressor uses a rotating disc with blades or an impeller to force gas to the rim of the impeller, increasing the gas’s velocity. The machine’s diffuser section then converts this velocity energy into pressure. Centrifugal compressors are often used in heavy industry and in continuous operation environments. They are usually stationary. Their power can range from hundreds to thousands of horsepower. With a multi-stage system, they can increase the output pressure to over 10,000 lbf/in² (69 MPa).
Many artificial snowmaking systems use this type of compressor. They can be driven by internal combustion engines, superchargers, or turbine engines. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium-sized gas turbine engines.

5. Mixed-Flow Compressor

A mixed-flow compressor is similar to a centrifugal compressor, but the velocity at the rotor exit is symmetrical. A diffuser is often used to convert the mixed flow into an axial flow. A mixed-flow compressor has a smaller diameter diffuser than an equivalent centrifugal compressor.

6. Scroll Compressor

A scroll compressor, similar to a rotary screw device, consists of two intermeshing spiral-shaped scrolls to compress gas. Its output pressure is not as stable as that of a conventional screw compressor, so it is less used in industry. It can be used as an automotive supercharger and in air conditioning systems.

7. Diaphragm Compressor

A diaphragm compressor is used to compress hydrogen and natural gas. The compressor is usually placed on top of storage tanks to hold the compressed gas. Both oil-lubricated and oil-free compressors are widely used, as oil can enter the gas stream. However, for diving compressors, even the smallest amount of oil is unacceptable.

PART 5: FURTHER REFERENCES FOR THE SAFETY DOCUMENT FOR OPERATING PRESSURE EQUIPMENT

1. Group 3 Safety Training and Certification Services

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