Inspection and maintenance of pressure pipeline

Inspection and maintenance of pressure pipeline

When you step into the industrial zone, you will find pressure pipes everywhere. Some of them even smoke. You always feel that they are about to explode at any time.

But that’s the truth. Maybe it will explode. If you look at some pictures, you’ll understand.

These are the tragedies caused by improper operation or routine inspection.
Therefore, it is very important to master the daily inspection items and preventive measures of pressure pipeline accidents.

Characteristics of pressure pipeline

The so-called pressure pipeline refers to the use of pressure to transport gas, liquid, etc. But not all pipes can be called pressure pipes. There are two conditions:

• 1. Pressure > = 0.1MPa (gauge pressure);
• 2. Pipe DN > = 25mm features.

1. Pressure pipe is a piping system, which moves the whole body with one trigger.
2. The ratio of length to diameter of pipeline is very large, which is easy to lose stability, and the stress condition is more complex than that of pressure vessel.
3. The fluid flow state in the pipeline is complex, the buffer space is small, and the change frequency of working conditions is higher than that of pressure vessel (such as high temperature, high pressure, low temperature, low pressure, displacement deformation, wind, snow, earthquake, etc., which may affect the stress of pressure pipeline).
4. There are many kinds of pipe components and pipe supports, and all kinds of materials have their own characteristics and specific technical requirements.
5. There are more possible leakage points in the pipeline than in the pressure vessel, and there are usually five points in only one valve.
6. There are many kinds of pressure pipes, large quantity, design, manufacture, installation, inspection, application and management, which are quite different from pressure vessels.

Daily inspection and maintenance of pressure pipeline

Inspection items	Inspection content	The harm of the problem	Maintenance methods and measures
Pressure gauge	1. Whether the surface glass is broken; 2. Whether the indication is sensitive or not; 3. Whether the pressure pipe is unblocked; 4. Whether the lead seal is in good condition.	Incorrect indication may cause overpressure.	Regular inspection and maintenance.
Thermocouple thermometer	Whether the temperature indication is accurate.	Over temperature will cause stress corrosion and creep of pipeline materials.	Regular calibration and maintenance.
Safety valve	1. Whether there is foreign matter stuck in the middle of valve core spring; 2. Check whether the adjusting screw is loose; 3. Whether the spring and other parts are damaged and whether there is air leakage; 4. Whether the lead seal is in good condition; 5. Whether the lead seal of the block valve is in good condition.	1. Air leakage; 2. In case of overpressure, the safety valve can not take off, resulting in pipeline accidents.	Check when stopping or releasing pressure.
Bursting disc	1. Whether the diaphragm has defects; 2. Whether the catheter is unblocked.	Cause pipeline accident.	1. Pay attention to the inspection before installation; 2. Regular replacement as required.
Pipe support	1. Whether the support is loose or not; 2. Whether the pipeline has vibration or not; 3. Check whether the bracket is damaged.	1. The pipeline is broken due to wear and fatigue; 2. The pipeline stress increases.	Tighten the bolts or reinforce them.
Pipe support foundation	1. Whether the foundation sinks; 2. Whether the foundation has cracks.	The foundation damage makes the pipeline bear additional stress and threatens the safety production.	1. Regularly observe the foundation subsidence and take targeted measures; 2. Determine whether the crack continues to expand.
Insulation	1. Whether the main material is damaged, peeled off, damped or invalid; 2. Whether the damp proof layer is damaged; 3. Whether the outer protective layer is damaged or fallen off.	1. Heat loss of pipeline; 2. Corrosion; 3. The insulation structure lost its protection and was damaged too early.	1. Replace the insulation material; 2. The damage should be repaired in time.
Bolt	1. Whether it is rusted; 2. Whether it is loose.	1. The screw and thread are corroded; 2. Cause leakage.	1. Apply antirust oil; 2. Tighten the bolts.

Preventive measures for pressure pipeline

The following pressure pipes shall be provided with safety valves

• 1. Safety valve shall be set on the outlet pipe of positive displacement pump such as electric reciprocating pump and gear pump. The vent pipe of the safety valve should be connected to the pump pipe, and the emergency shutdown interlock device should be set (except for the equipment with safety valve);
• 2. A safety valve shall be set at the outlet of each section of the combustible gas reciprocating compressor, and the vent pipe of the safety valve shall be connected to the inlet pipe of each section of the compressor or the first section of the compressor;
• 3. The safety valve shall be set in the pipeline where the combustible gas and liquid may expand beyond the design pressure when heated;
• 4. Safety valves or other safety measures should be set on the liquefied hydrocarbon pipeline which may be closed at both ends and lead to pressure rise;
• 5. When the equipment connected with the outlet of blower, centrifugal compressor, centrifugal pump or steam reciprocating pump can not bear its maximum pressure, the outlet pipeline of the above pump shall be equipped with safety valve.

Electrostatic grounding of pipeline

• 1. In the pipeline conveying flammable and explosive liquid or gas, the flow of materials along the pipeline and the process of entering and leaving the container from the pipeline will produce static electricity. The accumulation of a certain amount of electrostatic charge will produce electrostatic fault and electrostatic disaster.
• 2. Especially for high temperature and high pressure, flammable and explosive, toxic and harmful chemical plants, ensuring the safety of static electricity and preventing static electricity failure and static electricity disaster are the conditions for maintaining normal production order.
• 3. The metal parts of the non conductor pipe section must be grounded, especially the metal joint in the middle, to prevent the accumulation of static electricity and electrostatic discharge.

Correct selection of pipeline materials

• 1. Strictly carry out non-destructive inspection for material defects, especially for castings, forgings and high-pressure pipes. If any defective material is found, it shall not be put into use.
• 2. After installation, hydraulic test shall be conducted, and the test pressure shall be 1.5 times of the working pressure.
• 3. The form and material of steel pipe shall be selected correctly according to the process conditions of the pipe, and it shall not be replaced or misused at will.
• 4. Conduct appearance inspection and non-destructive inspection on the weld of pipeline to ensure the welding quality.

Source: China Pressure Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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