Petrochemical pipeline installation
Petrochemical pipeline installation is a complex specialty, which is characterized by large quantity of installation work, high quality requirements and long construction period. With the progress and development of technology in recent years, new construction methods are constantly adopted. At the same time, the state has issued new acceptance specifications, and the construction process content, processing methods, project quality acceptance standards of process pipelines have changed.
(I) Process pipelines construction preparation generally includes technical preparation, material preparation and construction team preparation. The specific work is as follows:
- 1. Be familiar with and review drawings and design documents, and timely participate in design disclosure.
- 2. Find out the project content, quantity and workload.
- 3. Prepare construction technical scheme of pipeline engineering and organize technical disclosure.
- 4. Organize welding process test and evaluation.
- 5. Prepare construction equipment and tooling facilities.
- 6. Organize the construction team, for the construction of new materials, do a good job in the training of construction personnel, make them master the technical operation essentials, and ensure the project quality.
- 7. Water, electricity, gas (steam) and paved roads shall meet the construction requirements.
(II) Through the above specific work, ensure that the pipeline works meet the following conditions:
- 1. The pipeline engineering design data and documents are complete, and the construction drawings have been reviewed jointly.
- 2. The construction scheme or technical measures have been approved.
- 3. The site prefabrication plant has the prefabrication conditions, and the temporary facilities meet the construction needs.
- 4. The reserves of pipes, pipeline fittings, valves, etc. have reached more than 60%, and other materials have appropriate reserves, and can enter the site successively to ensure continuous construction.
- 5. Construction machines and tools can enter the site according to the plan, and can ensure normal operation.
- 6. The construction personnel have received training or technical disclosure, and can be mobilized as scheduled at any time.
- 7. The progress of civil engineering and equipment installation has met the requirements of pipeline construction.
Due to the different mechanical equipment and management level of construction units in different regions and departments, the specific construction methods are not the same. The general construction procedures and methods of process pipeline are briefly introduced below.
We usually understand the operation process which is indispensable and independent in the construction as the construction process. The budget estimate index is a synthesis of the budget quota sub items on the basis of the industry budget quota, including the process of pipeline installation, pipeline fitting installation, flange installation, water pressure test, X-ray NDT, γ ray NDT, weld heat treatment, leakage test and pipeline purging.
(I) combination of pipeline installation procedures
The installation of pipes, pipeline fittings and flanges combines the cleaning and inspection, pipeline straightening, pipeline cutting, groove processing, welding and other processes of pipes and pipeline fittings.
1. Cleaning and inspection of pipes and fittings:
Before installation, the pipes shall be cleaned and inspected to remove dirt and impurities, and the appearance inspection shall be carried out according to the current national specifications. Unqualified pipes shall not be used.
The inspection of materials mainly includes the following points:
Inspection of steel pipe
Before using the steel pipe, check the specification, quantity and mark of the pipeline according to the design requirements;
Whether the pipeline has defects such as crack, shrinkage cavity, slag inclusion, folding, double skin, etc.
In Sha class pipes, the outer surface of pipes with design pressure equal to or greater than 10MPa shall be subject to NDT one by one according to the regulations, and there shall be no linear defects.
All steel pipes shall be provided with quality certificates. If the steel number and heat number of the arrived pipes do not conform to the quality certificates or have any objection to the characteristic data, the supplier shall verify or trace them to the product manufacturer according to the corresponding standards. The batch of pipes shall not be used before the objection is resolved;
Inspection of valves
Valves shall be subject to shell pressure test and sealing test one by one. Unqualified ones shall not be used.
The shell test pressure of the valve shall not be less than 1.5 times of the nominal pressure, and the test time shall not be less than 5min. The sealing test should be carried out under the nominal pressure, and it is qualified if the sealing surface of the valve disc is not leaking. The chloride ion content of water used for pressure test of stainless steel valve is ≤
The qualified valves shall be drained and dried in time. Fill in “valve test record” as per sh3543-2007
The safety valve shall be debugged according to the opening pressure specified in the design document. During pressure regulation, the pressure shall be stable, and the opening and closing test of each safety valve shall not be less than 3 times. After commissioning, fill in “safety valve adjustment test record” as per sh3503-2007.
Inspection of flange
The nominal pressure grade, connection type and sealing surface type of flange shall conform to the provisions of design documents and relevant standards;
The forging surface shall be smooth and free of forging scars, cracks and other defects;
The flange shall be marked with steel seal on the outer edge;
Inspection of fasteners
The thread of stud and nut shall be complete without scratch, burr and other defects. The studs and nuts shall be well matched without looseness or jamming;
There shall be no cracks, dents, wrinkles, cuts, damages and other defects on the surface of studs and nuts.
For alloy steel studs and nuts for pipes, 5% of each batch shall be sampled and no less than 1 shall be subject to spectral analysis;
The processing accuracy and roughness of thread, sealing surface and groove shall meet the design requirements or manufacturing standards.
2. Pipeline straightening
After leaving the factory, pipes are generally transported for many times in long and short distance, and finally arrive at the place of use. In the process of transportation and loading and unloading, it is very difficult to avoid the collision and falling pressure on the pipe, which causes the pipeline deformation. In order to make the pipeline construction meet the acceptance standard and basically achieve horizontal and vertical, it is necessary to straighten the pipe. The commonly used straightening methods are manual straightening and semi mechanical straightening. The tubes with smaller diameters are usually straightened by hand; the diameter of pipes is larger than 50mm, which is adjusted by the screw straightener, sometimes it needs heating and straightening after special conditions. When the diameter of pipes is larger than 200mm, it is generally not easy to bend and deform, so it is seldom needed to straighten.
3. Pipeline cutting
pipeline cutting is to cut a section of pipeline with size requirements on a longer pipe. According to the requirements of the specification, different cutting methods shall be adopted for pipes of different materials.
Carbon steel pipeline and alloy steel pipeline should be cut mechanically. When oxyacetylene flame cutting is used, it must be ensured that the size is correct and the surface is flat.
Stainless steel pipeline and non-ferrous metal pipeline shall be cut by mechanical method or plasma method. Special grinding wheel shall be used for cutting or grinding stainless steel and titanium pipes.
Galvanized steel pipeline should be cut by hacksaw or mechanical method.
pipeline cutting is an important process. The quality of pipeline cutting has a direct impact on the next process groove processing and nozzle group.
The cut quality of the pipeline shall meet the following requirements:
- The cut surface shall be flat and free of cracks, double skin, burr, convex concave, shrinkage, slag, oxide, scrap iron, etc.
- The inclination deviation △ of the end face of the incision shall not be greater than 1% of the outer diameter of the pipe, and shall not exceed 2mm.
4. Groove processing
Groove processing is an effective measure to ensure the welding quality of pipeline orifice. There are many types of bevels. The following aspects should be considered when selecting the type of bevels:
- (1) Ensure the welding quality;
- (2) Convenient operation during welding;
- (3) Saving electrode;
- (4) Prevent the nozzle from deformation after welding.
The groove types commonly used for pipeline welding are as follows:
- (1) I-groove;
- (2) V-groove;
- (3) U-groove.
Type I groove is applicable to the welding of nozzle with the thickness of pipeline wall less than 3.5mm. According to the wall thickness, adjust the gap between the butt joints to ensure the weld penetration. In this kind of weld, the pipeline wall does not need chamfering, in fact, it does not need to process groove. As long as the perpendicularity of the pipeline cut can ensure the gap requirements of butt joint, it can be directly butt welded.
V-groove is suitable for the welding of medium and low pressure steel pipes. The angle of the groove is 60 ° ~ 70 °, and the root of the groove has a blunt edge, with a height of 1 ~ 2mm.
U-groove is suitable for welding of high-pressure steel pipe, and the thickness of pipeline wall is between 20-60mm. The root of the groove has a blunt edge, with a thickness of about 2mm.
The groove processing form and size of pipes shall meet the requirements of design documents. Mechanical method, plasma arc, oxyacetylene flame and other hot processing methods shall be adopted for pipeline groove processing. After the groove is processed by hot working method, the oxide skin and slag on the groove surface and the surface layer affecting the joint quality shall be removed, and the uneven part shall be polished and leveled.
Pipes of grade Sha pipes shall be machined by mechanical method; pipes of grade SHB pipes shall be machined by mechanical method. When oxyacetylene flame or plasma cutting is used, the surface layer that affects the welding quality must be removed after cutting.
Welding is the main form of pipeline connection. There are many welding methods, including gas welding, arc welding, argon arc welding, argon arc welding and carbon dioxide gas shielded welding.
Before welding, the pipeline cut and groove shall be checked to see if they meet the quality requirements, and then the pipeline orifice shall be assembled. During the assembly, the inner wall shall be flush and the amount of inner wall misalignment shall meet the requirements. According to the requirements, the thickness of general pipes shall not exceed 10% of the wall thickness and shall not be more than 2mm; the thickness of grade Sha pipes shall not exceed 10% of the wall thickness and shall not be more than 0.5mm; the thickness of grade SHB pipes shall not exceed 10% of the wall thickness and shall not be more than 1mm. For the assembled nozzle, spot welding shall be carried out first. According to the diameter of the pipe, spot welding shall be carried out in 3 to 4 places, and then the nozzle after spot welding shall be welded.
Welding equipment and inspection equipment shall have stable parameters, flexible adjustment, safe and reliable performance, and meet the requirements of welding process.
Groove form: V-groove shall be made for butt joint.
Schematic diagram of groove
The setting of pipeline welds shall be convenient for welding and inspection, and shall meet the following requirements:
The clear distance between the weld and the edge of the support shall not be less than 50mm.
The distance between two adjacent circumferential joints of straight pipe shall not be less than 100mm, and shall not be less than the outer diameter of steel pipe.
It is not suitable to open holes on the weld and its edge, otherwise, the weld within the range of one time of the hole diameter around the opened hole shall be subject to radiographic inspection.
Before using the electrode, it must be baked to be qualified.
If the welding rod is qualified but not used or has been distributed and not used up, it shall be used for more than 4 hours under normal temperature, and shall be baked again before the next use. The baking times of the same electrode shall not exceed twice.
Each welded junction of prefabricated pipeline must be marked, especially alloy steel and special material pipeline. Mark the welding date, welder number and crater number, and paint each pipe section with pipeline number and pipeline section number according to the single line diagram, so as not to cause confusion in installation, make the crater untraceable, cause the handover data inconsistent with the physical object, and make mistakes in the use position of special material pipeline, etc.; the prefabricated pipe section must be closed with the end nozzle.
The following conditions shall be met for pipeline installation:
- The equipment and structure have been installed and accepted according to the design documents;
- The pipeline components shall have the required quality certification documents and pass the inspection;
- The pipeline components have been checked according to the design requirements, and their materials, specifications and models are correct; the pipeline prefabrication has been completed and meets the requirements;
- Before pipeline installation, NDT, external anti-corrosion and other processes shall be completed and meet the requirements;
- The inside of the pipeline components and the vicinity of the welding joints have been cleaned, and there is no oil or debris.
The slope direction and gradient of pipeline installation shall meet the design requirements.
Temporary supports shall not be welded during the installation of pipes. If welding is required, relevant regulations of welding process shall be met.
If the pipeline installation is interrupted, the open pipe orifice shall be closed in time. When installing the connected pipes, the internal part of the pipes installed in the early stage shall be inspected, and the pipes shall be installed after confirming that there is no foreign matter in the pipes.
General requirements for pipe installation
The process pipeline entering the construction site for installation shall meet the following specific requirements during installation:
Before the installation of pipe section, internal self inspection shall be carried out to ensure there is no dirt in the storage.
When connecting pipes, do not use strong butt joint to avoid internal stress and pipe deformation.
Before installing the flange, the sealing surface shall be inspected without defects, and the rust, burr and dust on the flange shall be removed. The pipeline inserted by socket welding flange shall have a thermal expansion gap of 1-1.6mm during butt joint.
During flange connection, the parallelism and concentricity of the joint surface shall be maintained, and the corresponding flange surface shall be flat before the gasket is placed.
The alignment shall meet the requirements to ensure the free penetration of bolts. The installation of stud bolts shall keep the two ends of bolts symmetrical and uniform, the length of exposed thread shall be approximately the same, and shall not be greater than 2 times the pitch.
The pipe shall be correctly installed with sliding, guiding and fixing brackets. The welding of pipe bracket shall be carried out according to the standard drawing of bracket without leakage.
Defects such as welding, under welding or welding cracks. When the pipe is welded with the support, the steel pipe shall be free of undercut, burn through and other phenomena.
Specific method of pipeline installation
The pipeline shall be prefabricated according to the single line diagram.
When prefabricating the matching flange of the equipment, it is necessary to assemble and spot weld first, and then weld after alignment during installation.
In case of any discrepancy between the installation size of the drawing and the site, the actual size of the site shall prevail.
The on-site installation of process pipeline is the difficulty of quality control, which is restricted by the on-site installation conditions and environmental factors. If necessary, appropriate quality assurance measures shall be taken;
The welding joints welded on site are generally fixed joints, and the quality is difficult to control, so it is necessary to control the following aspects:
In the prefabrication stage, each welder shall be observed and the qualification rate shall be counted, because human is the first element in the quality control link, and the quality of nozzle field assembly shall also be carried out according to the requirements;
In case of wind, snow, rain, high humidity and other weather, effective protective measures must be taken before welding is allowed;
It is very difficult for the alloy steel pipe to be charged with argon gas, so it is the weakest link of on-site quality control, and also the most important link of quality inspection. It can take flux skin or flux cored wire for backing, but this process must pass the welding process assessment and approval, and the welder has passed the examination and qualified.
(II) Inspection of welds
After each welded junction of the pipeline is welded, the slag skin and splashes on both sides of the weld shall be removed, the weld surface shall be cleaned, and the appearance inspection shall be carried out to check whether there are cracks, air holes, slag inclusions and other defects in the weld. The appearance inspection quality of the pipeline weld shall conform to the relevant provisions of the current national standard code for construction and acceptance of field equipment and industrial pipeline welding engineering (GB50236). 。
NDT of weld surface shall be carried out by magnetic particle or liquid penetrant inspection according to the provisions of design documents. When defects are found on the weld surface, they shall be eliminated in time. After elimination, they shall be inspected again until they are qualified. It is specified that the pipeline welds must be subject to radiographic inspection or ultrasonic inspection, and the welds welded by each welder participating in the welding shall be spot checked according to the specified proportion. The following pipeline welds shall be subject to 100% radiographic inspection, and their quality shall not be lower than level II:
- (1) Pipeline for transporting highly toxic fluid;
- (2) Pipeline for conveying flammable and toxic fluid with design pressure greater than or equal to 10MPa or design pressure greater than or equal to 4MPa and design temperature greater than or equal to 400 ℃;
- (3) Pipeline for conveying non combustible and non-toxic fluid with design pressure greater than or equal to 10MPa and design temperature greater than or equal to 400 ℃;
- (4) Low temperature pipeline with design temperature less than – 29 ℃;
- (5) Other pipes requiring 100% radiographic inspection in the design documents.
On each pipe, the number of welded joints for random inspection shall not be less than one. If a welder’s welded joint is found to be unqualified, double spot check and flaw detection shall be conducted for the welded joint according to the specified proportion. If it is still unqualified, NDT shall be conducted for all the welded joints in the pipeline. All welds that fail to pass the NDT inspection must be repaired, and the repaired welds shall still be inspected according to the original specified method.
When the design does not specify the percentage of radiographic testing for welded joints at all levels of the pipeline, the provisions in Table 1 can be followed.
Due to the high requirements of the current specification for the quality of the weld, in order to ensure the quality of the weld, the welder shall be equipped with a portable electric grinder. During the welding process, the defects such as slag inclusion and porosity between the weld layers shall be ground off with the grinding wheel at any time and then the welding can be continued.
In an engineering project, after the installation of the process pipeline of a system, the system strength test and air tightness test can be carried out for the pipeline according to the design provisions, the purpose of which is to check the pressure of the pipeline and the tightness of each connection part. Generally, the hydraulic test is used for the pipeline conveying liquid, and the gas test is mostly used for the pipeline conveying gas.
Before the pipeline pressure test, the following conditions shall be met:
- (1) Except for painting and heat insulation, the pipeline installation within the pressure test scope has been completed in accordance with the design drawings, and the installation quality meets the relevant regulations.
- (2) The expansion joint on the pipeline has been provided with temporary restraint device.
- (3) The pressure gauge for the test has been verified, and within the weekly inspection period, its accuracy shall not be lower than level 1.5, the full scale value of the gauge shall be 1.5-2 times of the maximum pressure measured, and the pressure gauge shall not be less than two pieces.
- (4) The liquid medium or gas meeting the pressure test requirements has been prepared.
- (5) Qccording to the test requirements, the pipeline has been strengthened.
- (6) Before the pressure test, the data required by the specification has been rechecked for the pipeline conveying highly toxic fluid and the pipeline with design pressure greater than or equal to 10MPa.
- (7) The pipeline to be tested and unrelated system have been separated by blind plate or other measures.
- (8) The safety valve, bursting plate and instrument elements on the pipeline to be tested have been removed or isolated.
- (9) The test scheme has been approved and technical disclosure has been carried out.
1. Liquid pressure test
In general, the hydraulic test is carried out with clean water. If there are special requirements in the design, the test shall be carried out according to the design regulations.
For the procedure of water pressure test, first of all, make preparations before the test. Install the temporary water injection and drainage pipeline for test; install the vent valve at the highest point and the end of the pipeline; install the drain valve at the lowest point of the pipeline; install the pressure gauge at the highest point, and the test pressure shall be subject to the gauge.
If the installed valves and instruments on the pipeline are not allowed to carry out the hydraulic test at the same time with the pipeline, the valves and instruments shall be removed first, and the pipeline length occupied by the valves shall be connected and connected with the temporary short pipeline; a blind plate shall be added in the middle of the flange connecting the pipeline and the equipment to make the whole pipeline system in the closed state.
After the above preparations are completed, start to inject water into the pipeline. When injecting water, open the vent valve. When the vent valve at the end of the pipeline runs water, close the vent valve immediately. When the vent valve at the highest point of the pipeline of the whole system also runs water, it means that the pipeline of the whole system has been filled with water and the vent valve at the highest point is closed. At this time, check the whole system pipeline, if there is no leakage, the pressure can be increased. The pressure rise shall be carried out slowly. After the specified test pressure is reached, the pressure shall be stopped for 10 minutes. It is qualified if there is no leakage through inspection and no deformation of pipeline through visual inspection.
The pressure standards for various pipeline tests are generally specified in the design. If not, they can be carried out in accordance with the pipeline construction and acceptance specifications.
After the test pipes are inspected to be qualified according to the regulations, the water in the pipes shall be drained off. Before drainage, the vent valve at the highest point of the pipes shall be opened first, then the drain valve shall be opened, and the water shall be put into the drainage pipes. Finally, remove the temporary pipes, connecting pipes and blind plates for the test, reset the removed valves and instruments, connect all flanges, and fill in the pipeline system test records.
For pipeline pressure test, if the ambient air temperature is lower than 0 ℃, the pipeline shall be dried with compressed air immediately after water drainage to avoid the pipeline from being damaged by accumulated water.
2. Gas pressure test
According to the provisions of sh3501, the following pipes can be subject to air pressure test:
- (1) Pipeline system with nominal diameter less than or equal to 300 mm and test pressure less than or equal to 1.6 MPa;
- (2) Pipeline system with nominal diameter greater than 300 mm and test pressure equal to or less than 0.6 MPa.
Most of the gases used in air pressure test are compressed air or inert gas. Before the test, air must be used for pre test, and the test pressure should be 0.2MPa. During the test, the pressure shall be increased slowly step by step. When the pressure rises to half of the specified test pressure, if no abnormality or leakage is found, continue to increase the pressure step by step according to 10% of the test pressure, stabilize each stage for 3 minutes until the test pressure is stabilized for 10 minutes, and then reduce the pressure to the design pressure. The pressure stop time shall be determined according to the needs of leak detection. The foaming agent is qualified if it does not leak.
(3) Leakage test
Leakage test must be carried out on the pipeline conveying highly toxic fluid, toxic fluid and combustible fluid. Leakage test shall be carried out according to the following provisions:
- (1) The leakage test shall be conducted after the water pressure test is qualified, and the test medium shall be air.
- (2) The leakage test pressure shall be the design pressure.
- (3) Leakage test can be carried out in combination with test run.
- (4) Lhe leakage test shall focus on the inspection of valve packing culvert, flange or screw connection, vent valve, vent valve, drain valve, etc. The foaming agent is qualified if it does not leak.
- (5) If the pipeline passes the air pressure test and has not been disassembled after the test, the leakage test may not be carried out.
After the pipeline system passes the pressure test, it shall be purged. The method of purging shall be determined according to the use requirements of the pipeline, the working medium and the degree of dirt on the inner surface of the pipeline. For liquid or gas pipelines with a nominal diameter greater than or equal to 600mm, manual cleaning shall be used; for liquid pipelines with a nominal diameter less than 600mm, water cleaning shall be used; for gas pipelines with a nominal diameter less than 600mm, air purging shall be used; for steam pipelines, steam purging shall be used; for non thermal pipelines, steam purging shall not be used.
Before purging, the pipeline system shall meet the following requirements:
- (1) Orifice plate, flange connected regulating valve, important valve, throttle valve, safety valve, instrument, etc. shall not be installed. For the above-mentioned valves and instruments welded, protective measures such as by-pass or removing the valve head and valve seat plus protective sleeve shall be taken.
- (2) The firmness of the pipe supports and hangers shall be inspected and reinforced if necessary.
- (3) Equipment and pipes that are not allowed to be purged shall be isolated from the purging system.
The pipeline purging shall be carried out in sequence according to the main pipe, branch pipe and drain pipe. The booty blown out shall not enter the qualified pipeline. The dirty liquid discharged by cleaning shall not pollute the environment and shall not be discharged anywhere.
1. Water rinse
In the process pipeline, water flushing is generally required for all pipelines conveying liquid medium. Drinking water, industrial water or steam condensate are often used for flushing. During flushing, large flow rate should be used, the flow rate of water in the pipe should not be less than 1.5m/s, and the cross-sectional area of the discharge pipe should not be less than 60% of the cross-sectional area of the pipe to be flushed, and the smooth and safe discharge pipe should be ensured. The water flushing shall be carried out continuously, and the flushing quality shall meet the design requirements. If there is no clear provision in the design, the water color and transparency at the outlet shall be consistent with the water visual inspection at the inlet.
2. Air purging
Air purging is generally adopted for all pipelines conveying gas medium in process pipeline, and oil-free gas shall not be used for purging of oil pipeline.
The large compressor of the production unit shall be used for air purging. The purging pressure shall not exceed the design pressure of the vessel and pipeline, and the flow rate shall not be less than 20 m/s.
The inspection method of air purging is to set a white cloth or target plate coated with white paint at the exhaust port of the purging pipeline. If there is no rust, dust, moisture and other impurities on the target plate within five minutes, it shall be qualified.
3. Steam purging
The method of steam purging is applicable to the pipes conveying power steam. Because the steam purging temperature is high, the pipes need to expand and displace after being heated. These factors are considered in the design. Compensators are installed on the pipes, and the needs of displacement after being heated are also considered in the pipe supports and hangers. Generally, these factors are not considered in the design of pipelines conveying other media, so steam purging is not applicable. If steam purging must be used, necessary measures must be taken and the thermal displacement of pipelines shall be checked.
For steam purging, firstly input a small amount of steam into the pipe, slowly raise the warm pipe, timely drain the water, conduct purging after constant temperature for one hour, then stop the steam to reduce the pipe to the ambient temperature, and then warm the pipe for temperature rise and constant temperature, conduct the second purging, which shall be repeated for at least three times, and the method of purging one pipe at a time shall be adopted. If it is indoor purging, the exhaust pipe of steam must be led to the outdoor and erected firmly. The diameter of the exhaust pipe shall not be less than the diameter of the pipe to be purged.
The inspection method of steam purging: for the middle and high pressure steam pipes and the pipes at the inlet of steam turbine, the flat and smooth aluminum plate target shall be used; for the low pressure steam, the planed wood plate target shall be used for inspection; the target plate shall be placed at the outlet of exhaust pipe, and the target plate shall be inspected according to the regulations. If there is no dirt, it is qualified.
4. Pipe degreasing
Some pipelines are not allowed to have any oil traces due to the requirements of the transmission medium, so they need to be degreased. Before degreasing, the degreasing plan shall be formulated according to the pipe specification, working medium, degree of dirt and site conditions. For steel pipes and pipe fittings with obvious oil traces or serious corrosion, the oil traces and rust shall be removed by steam blowing, sandblasting or other methods before degreasing. Degreaser shall be selected according to the design requirements, with certificate of conformity. The site selection of pipeline degreasing can be indoor or outdoor, but shall not be polluted by rain, snow and dust.
5. Pickling and passivation
For pipes with special cleaning requirements on the inner surface, pickling is generally carried out before putting into production, and passivation is carried out after pickling as required. If there are obvious oil spots in the pipeline, necessary pre degreasing treatment shall be carried out before pickling. The pickling solution shall be prepared according to the specified formula and sequence, and shall be stirred evenly. During pickling, acid leakage accident shall be prevented. The operator shall have necessary protection. The wastewater and waste liquid after pickling shall be treated and can be discharged only after meeting the environmental protection requirements. For acid pickling and passivation pipes, the pipes shall be closed timely after passing the inspection, and protective measures shall be taken to prevent re pollution.
Source: China Stainless Steel Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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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