Regarding the connection method of the N2 pipeline

In our newly installed equipment, except for the water used for daily purposes (such as that for eye washers and in the outdoor areas), which is connected via threaded fittings, everything else is welded together

It mainly depends on the pipeline pressure; if it’s four to five kilograms, there’s no major issue

There’s no problem when the nitrogen pressure is not high.

1 Pipe threaded connection (galvanized steel pipes, plastic-lined galvanized steel pipes). 2 Pipe flanged connection (requires disassembly, used for connection to equipment valves, etc.). 3 Pipe welding: Electric or gas welding can be used for steam pipes with a working pressure of over 0.1 MPa, heating pipes with a diameter of 32 mm or more, as well as fire protection pipes in high-rise buildings. 4. Pipe socket connection 5. Pipe adhesive connection: (UPVC pipes, ABS pipes) 6. Pipe crimp connection (aluminum-plastic composite pipes) 7. Pipe heat fusion connection (currently, it is mostly used for the installation of PP-R pipes and PB pipes in domestic water supply systems) 8. Copper pipe connection. In building water supply systems, copper pipes are used, and the main methods of connecting them are crimping and welding.

I. Pipe threaded connection (galvanized steel pipes, plastic-lined galvanized steel pipes) 1. Cutting the pipe: Based on the site survey sketch, mark lines on the selected pipe and cut it along those lines. To cut a pipe with a grinding saw, the pipe should be placed on the grinding saw’s clamps, aligned according to the marks, and then cut. When breaking the tube, apply even pressure to the handle; do not use excessive force. After breaking the tube, remove any iron film or burrs from the cut surface of the tube. b To cut the pipe with a hand saw, fix the pipe in the pressure clamps of a press, align the saw blade with the marked line, and push the saw with both hands. The saw blade must remain perpendicular to the axis of the pipe; apply even force when pushing and pulling the saw, and ensure that the cut goes all the way through – the pipe must not be twisted or broken to prevent deformation of the pipe’s end surface. 2. Tapping: For the cut pipes, tap threads in stages according to the pipe diameter; generally, pipes with a diameter of 15–32 mm require 2 tapping sessions, those with a diameter of 40–50 mm need 3 sessions, while pipes with a diameter of 70 mm or more are best tapped 3–4 times. a Use a thread rolling machine to create threads: clamp the pipe in the machine’s chuck, leaving an appropriate length before tightening the chuck; align it with the corresponding die, insert the die, set it at the appropriate position on the scale according to the pipe diameter, press down the fixing trigger, align the lubricant tube with the threaded end, start the machine to move the plate forward, and once the threads have been formed to the desired length, gently release the trigger. b Use a manual thread-forming die to create threads: first loosen the fixing trigger, move the die’s disc to zero degrees, insert the dies in order, align the disc with the desired scale, then tighten the fixing trigger. Place the pipe inside the pressure fixture, leaving enough length to secure it, gently fit the die over the pipe so that it is snug but not too tight. Then use both hands to push the die forward to form 2–3 threads, after which stand to the side and turn the die while applying even pressure. When the threads are almost formed, gently release the trigger and use the machine to retract the die, ensuring that the threads have the proper taper. 3 Fitting pipes: Install the pipe fittings onto the pipes that already have threads, based on the site survey sketches. When installing fittings, bring the required fittings into the pipe threads and check the tightness (it is generally appropriate to insert them 3 threads with the hand). Apply lead grease to the threads, wrap them with hemp, then insert the fittings; afterwards, use pipe wrenches to tighten the fittings so that 2-3 threads are exposed. Remove the hemp ends, wipe off the lead grease, label the fittings, and place them in the appropriate location until they can be straightened. b Select an appropriate pipe wrench based on the diameter of the pipe fittings. 4. Straightening the pipe segment: Straighten the pipe segment with the fittings already installed, before proceeding with installation. Apply lead grease to the threads of the pipe section where the fittings are installed, in order to connect two or more sections. When making the connections, one must consider not only the direction of the reserved openings but also the curvature of the pipes; after aligning them properly, adjust the direction of the reserved openings to the appropriate position and ensure they remain straight. After the b pipe sections are connected, before straightening them, it is necessary to check according to the design drawings to ensure that their diameters, the direction of the reserved openings, and the areas where the diameter changes are correct. To straighten a pipe segment, it should be placed on a pipe straightening rack or platform; it is generally advisable to have two people working together – one person checks the end of the pipe segment visually, while the other uses a hammer to strike the bent area. They continue to strike and observe until the pipe segment is completely straight. Marks should be made at the connection points between the pipe segments, after which one or several segments are removed and replaced with another segment or segments until straightening is complete. For pipes that are excessively bent at the joints or those with a large diameter, it is possible to use an oven or gas welding to heat them to 600–800°C (a bright red color). Once heated, the pipes should be placed on a pipe rack and rotated continuously so that their own weight helps to straighten them. Alternatively, wooden blocks can be placed under the heated area and a hammer can be used to straighten the pipes. After straightening, the pipes must continue to be rotated until they cool down; once the temperature has dropped to an appropriate level, machine oil should be applied to the heated areas. Any threaded part that has been heated and straightened must be marked; it should then be removed, re-coated with lead grease and wrapped in hemp, before the pipe section is tightened against the mark. For the pipe section equipped with valves, when straightening it, the valve cover should be removed first; the area around the valve should be padded properly before striking it, in order to prevent the valve body from cracking. f Galvanized carbon steel pipes shall not be straightened by heating. It is not allowed to damage the pipe segment when straightening it. II. Pipe flange connections (requiring disassembly and connection to equipment valves, etc.) 2.1 Where pipe sections are connected using flanges or where pipe sections are connected to flanged valves, standard flanges must be selected in accordance with the design requirements and operating pressure. 2.2 The diameter and length of the coupling bolts for the flanges shall meet the requirements of the specifications. When tightening the flange bolts, they should be tightened symmetrically; the exposed threads of the tightened bolts should be 2–3 turns, and this amount should not exceed half of the bolt’s diameter. 2.3 For flange connections, rubber gaskets with a thickness of 3 mm are generally used for water (cold water) supply systems, while asbestos-rubber gaskets with a thickness of 3 mm should be used for heating, steam, and domestic hot water pipelines. The gasket must be concentric with the pipe diameter and must not be displaced. III. Pipe Welding 3.1 According to design requirements, steam pipes with a working pressure of over 0.1 MPa, heating pipes with a diameter of 32 mm or more, and fire protection pipes in high-rise buildings can be joined using electric or gas welding. 3.2 During pipeline welding, measures should be taken to protect against wind, rain, and snow. When the ambient temperature in the welding area is below -20°C, the weld area must be preheated; the preheating temperature should be between 100–200°C, with a preheating length of 200–250 mm. 3.3 Generally, pipeline welding is carried out in a butted configuration with alignment. 3.4 Before welding, align the axes of the two pipes; first, spot-weld the ends of the pipes firmly. For pipes with a diameter of 100 mm or less, three spot welds are sufficient, while for pipes with a diameter of 150 mm or more, four spot welds are recommended. 3.5 For pipes with a wall thickness of 5 mm or more, bevels should be created at the pipe ends where welding will take place. If gas welding is used to prepare the pipe bevels, the oxide scale on the surface of the bevels must be removed, and any uneven areas that could affect the quality of welding must be smoothed out. 3.6 When welding pipes to flanges, the pipe should first be inserted into the flange; 2–3 spot welds should be made first, and then the pipe should be aligned and leveled using a square before welding. The flange should be welded on both sides, and the welds on the inner side must not protrude beyond the sealing surface of the flange. IV. Socket Joint Connection of Pipes 4.1 Cement Mortar Joint: Generally used for socket joint connections of indoor and outdoor cast-iron drainage pipes. a To reduce the amount of mortar needed for fixing, the mortar can be applied in advance to certain pipes and fittings. Before applying the mortar, it is necessary to check whether the pipes and fittings have any cracks, pores, or other defects; moreover, the pipes and fittings should be aligned beforehand to ensure that there are no dimensional errors and that the gaps around the socket joint are within acceptable limits. When connecting pipes and fittings, they can be placed on a temporary fixing frame; the pipes and fittings should be inserted with the socket side facing up and the spigot side facing down, as specified in the drawings, and then the joint should be sealed with mortar. c When twisting the ash core, first use a hemp drill to drive green hemp or binding rope – which is slightly thicker than the gap surrounding the socket and spigot joints – into the socket; it is advisable to drive it in two loops (about one-third of the depth of the socket). The overlap between the sections of hemp should be at least 30 mm in length. After that, compress the hemp firmly, adjusting its position as you go while ensuring it is flattened. d After the hemp has been properly prepared, the packing mortar (with a water-to-cement ratio of 1:9) can be filled into the annular gaps of the socket in layers. First, use a thin tamping tool: fill the gaps with mortar with one hand while tamping it down with the other hand. Then, use a hammer and tamping tool to compact the mortar layer by layer until the gaps are completely filled. Use a tamping tool whose thickness matches the size of the annular gaps to level the mortar, until the tool gives a resilient feel when tapped on the mortar – at that point it is considered ready. The mixed ash for twisting should be used as soon as it is prepared; it is advisable to use up the mixed ash within one and a half hours. Additionally, the amount of water used should be adjusted accordingly based on the weather conditions. f When prefabricating two sections of pipe or two or more pipe fittings, the pipe or fittings with the gray cast iron already twisted should be placed at the upper part, while the gray cast iron in the lower part is twisted later, in order to reduce vibrations. After twisting the last gray cast, check whether the remaining gray casts are loose; if so, address the issue promptly. g The pre-fabricated pipe sections and fittings should be stacked in a flat area, laid flat and secured firmly; the gray cast iron surfaces should be wrapped with wet hemp rope, and they need to be kept moist through watering. Generally, it takes 48 hours at room temperature before they can be moved to the site for installation. During the severe cold periods of winter, effective anti-freezing measures must be taken for cast iron products. An appropriate amount of salt water can be added to the water used for plastering; the cast iron products must not be exposed to freezing conditions, and the storage temperature should be maintained above 5°C. Steam curing can also be employed if possible. 4.2 Asbestos-cement joints: Asbestos-cement twisted joints are generally used for the installation of indoor and outdoor cast-iron water supply pipes, which are created by mixing an appropriate amount of asbestos fibers into cement. 4.3 Lead joints: Generally used for laying cast iron water supply pipes inside industrial buildings. Lead joints can be employed when there are special design requirements, or for emergency repairs of outdoor cast iron water supply pipes, as well as in situations where it is necessary to start supplying water promptly at pipe connections. 4.4 Rubber ring joints: Generally used for the connections between pipes during the installation of outdoor cast iron water supply pipes. Pipes and fittings still require asbestos-cement sealing. V. Pipe bonding connections: (UPVC pipes, ABS pipes) 5.1 Pipe bonding should not be carried out in environments with high humidity; the work area must be kept away from sources of fire, and impact should be avoided, at -20°C. 5.2 Before bonding, pipes and fittings should have the inner side of the socket and the outer side of the spigot wiped clean using clean cotton yarn or dry cloth, to keep the bonding surfaces clean. If the surface is contaminated with oil, it should be cleaned using cotton yarn dipped in a solvent such as acetone. 5.3 When applying the adhesive with a brush, apply it first to the inside of the socket, and then to the outside of the spigot. When applying the socket sealant, it should be applied evenly and in an appropriate amount in an axial direction from the inside outward; there should be no missed areas or excessive thickness of the coating. 5.4 After applying adhesive to the spigot and socket, it is advisable to align them with the axis and insert them forcefully in one continuous motion within 20 seconds. The insertion depth of the pipe end into the socket should be determined based on the actual measured depth of the socket; a mark should be made on the surface of the pipe end at that depth, and after insertion the pipe should be rotated 90°. 5.5 Once the connection is made, the adhesive that has oozed out from the outside of the connector should be wiped clean immediately. Avoid applying force; let it sit until the joint has cured. Installation can proceed only after the joint is secure. 5.6 Adhesive joints should not be used when the ambient temperature is below 0°C, to prevent the adhesive from freezing. Do not use open flames or electric heaters to heat adhesives. VI. Clamp-type connection of pipes (aluminum-plastic composite pipes) 6.1 Cut the pipes to the diameter specified in the design requirements and to the length of the pipe segment as verified on site. Inspect the pipe end; if burrs, unevenness, or a terminal face that is not perpendicular to the pipe axis are found, they should be corrected ； 6.2 Use a dedicated scraper to cut a bevel on the inner polyethylene layer at the pipe opening; the bevel angle should be 20–30°, and the depth should be 1.0–1.5 mm. Clean the residue left from the beveling with clean paper or cloth ； 6.3 Round the pipe end using a rounding tool ； 6.4 Put the locking nut and C-shaped clamping ring on the tube, then push the core firmly into the tube until the opening of the tube reaches the base of the core ； 6.5 Move the C-type clamping ring to a position 0.5–1.5 mm away from the pipe opening, and then tighten the locking nut to the pipe fitting body. VII. Hot-melt joining of pipes (currently, it is mostly used for the installation of PP-R and PB pipes in domestic water supply systems) 7.1 Connect the hot-melt tool to power; operation can begin only after the indicator light indicating that the tool has reached the working temperature lights up ； 7.2 When cutting pipes, the end face must be perpendicular to the pipe axis. Pipe cutting is generally done using pipe cutters or pipe cutting machines; a sharp steel saw can be used if necessary, but the edges and burrs on the cut end of the pipe should be removed ； 7.3 The connection surfaces of pipes and fittings must be clean, dry, and oil-free ； 7.4 Use calipers and a suitable pen to measure and mark the hot-melt depth at the tube end. 7.5 When welding elbows or tees, it is necessary to pay attention to the direction as specified in the design drawings; the positions should be marked with auxiliary indicators along the straight line direction of the fittings and pipes ； 7.6 During connection, introduce the pipe end into the heat sleeve without rotation, to the indicated depth; simultaneously, push the pipe fitting toward the heating element without rotation until it reaches the specified mark. The heating time shall meet the requirements specified in the table above (or as specified by the manufacturer of the heat welding tool) ； 7.7 Once the heating time has elapsed, immediately remove the pipe and fittings from both the heating sleeve and the heating head, and insert them quickly, in a straight line without rotation, to the specified depth, so as to form a uniform flange at the joint ； 7.8 Within the processing time specified in the table above, the newly welded joint can still be adjusted, but rotation is strictly prohibited. VIII. Connection of copper pipes: In building water supply systems, copper pipes are used, and the main methods of connection are compression fitting and welding. (1) The card-type connection is convenient and straightforward to use; by selecting the right accessories, the connection can be made airtight, preventing leaks and enabling it to withstand sufficient pressure. Crimp connections are divided into two types: non-operable connectors of type A and operable connectors of type B. For type A connectors, the installation process involves selecting a crimp sleeve that matches the pipe specifications, cutting the pipe to the correct length, removing all burrs, and checking whether the pipe ends are clean and free of deep scratches or other defects. If the end of the tube is elliptical, use appropriate tools to round it out, then insert the tube into the sleeve until it reaches the retaining ring. Tighten the nut by hand and with a wrench until the clamp holds the tube in place; at this point, it will no longer be possible to turn the nut on the sleeve by hand. Now use two wrenches to tighten the nut by 1/3 to 2/3 of a turn. This causes the compression ring to bite into the tube, resulting in slight deformation of the tube. Operable joint type B: This joint can clamp both the inner and outer surfaces of the pipe, allowing it to provide support while also securing the copper pipe tightly. The connection method involves verifying that the specifications of the tube and the sleeves used are correct, then cutting the tube to the desired length with a fine-toothed saw, cleaning off any burrs on the inside and outside, fitting compression nuts and rings over the tube ends, using the appropriate flaring tool or punch to expand the tube ends, and finally placing the profiled tube properly into the tube ends and sleeves before tightening the compression nuts. First turn it by hand, then tighten it with a wrench for about a week, and a firm and secure joint will be created. (2) There are mainly two welding methods: soldering and brazing. The difference between the two lies in the different metal fillers used, the different fluxes, and the different applications. Using these welding methods requires personnel with professional qualifications to carry out the operations. Before brazing together 1 set of pipes, it is necessary to verify once again that the specifications and dimensions of the pipes and fittings meet the requirements for connection ； 2 According to the design drawings, the pipe length is measured on-site, ensuring accurate cutting. Cutting can be done using a rotary pipe cutter, or a steel saw or electric saw with no fewer than 13 teeth per centimeter. After cutting, the burrs at the pipe ends should be removed and the edges rounded off. 3 The spot welding strength is low; generally, a lap joint is used for the welds. The lap length is 6 to 8 times the wall thickness of the pipe; when the outer diameter of the pipe is 28 mm or less, the lap length is (1.2 to 1.5)D (mm). 4 Before welding, the outer surface of the copper tube at the welding site and the inner surface of the fittings should be polished using fine sandpaper, steel brushes, or sandpaper with other abrasives, in order to remove any oxides on the surface ； 5 Apply the paste-like or liquid flux evenly to the cleaned outer surface of the pipe and the inner surface of the fittings ； 5 Insert the copper tube into the fitting, push it all the way in and rotate it appropriately to maintain a uniform gap, then wipe away any excess flux from the extruded joint ； 6 Use a gas welding flame to evenly heat the joint until it reaches the brazing temperature ； 7 Use a filler metal to make contact with the joint that has been heated to a high temperature. When the temperature at the copper pipe joint is high enough to cause the filler metal to melt rapidly, it indicates that the temperature at the joint has reached the soldering temperature; at this point, heating can continue while the filler metal is added until the solder joint is fully filled ； 8 Remove the flame and allow the joint to cool and crystallize while at rest ； 9 Clean the residue at the joint. IX. Grooved Connection 9.1 Use a steel pipe cutting machine to cut the steel pipes to the desired length; the cuts should be smooth, and any burrs on the cut edges must be smoothed out using a grinder so that the ends are flat and smooth ； 9.2 Press the grooves using a dedicated grooving machine. The steel pipe whose grooves are to be processed is placed on the grooving machine and its tailstock. A level is used to adjust the horizontal position of the tailstock, the grooving machine itself, and the end face of the steel pipe, so that the end face of the steel pipe is in close contact with the end face of the grooving machine’s pulley guard; this means that the angle between the steel pipe and the end face of the grooving machine’s pulley guard is 90 degrees ； The grooving should be done gradually and continuously ； 9.3 Check that the rubber seal ring is the right size, apply lubricant to it, fit it at one end of a pipe segment, then attach the other pipe segment, positioning the seal ring in the center of the connection area ； 9.4 Slide the clamp over the rubber ring and fit the edges into the grooves ； 9.5 Insert the bolt with the deformation block into the bolt hole and tighten the nut. X. Flexible drainage cast iron pipe connections: Type A socket-gland rubber ring flange gland connection, Type W stainless steel clamp with rubber ring lining. XI. Thin-walled stainless steel pipes: 11.1 Clamp connection – a type of compression connection. Using the rapid hydraulic plier tool**, external force is applied to deform the stainless steel compression ring, allowing it to fit tightly around the steel pipe ； Fit the rubber seal ring again, tighten the stainless steel nut (the rubber seal ring, stainless steel nut, and pipe fitting are pre-assembled together at the time of manufacture) to connect it to the pipe fitting. Suitable for DN15, DN20. 11.2 Expansion Connection: An expansion tool marked with ** is used to expand the inner surface of a thin-walled stainless steel tube into a mountain-shaped platform flange; a rubber seal ring is placed at one end of the flange, and a stainless steel nut is tightened to connect it to the pipe fitting. Suitable for DN25～DN50. 11.3 Rubber seals: Depending on the requirements of the medium being transported, seals made of materials such as silicone rubber or EPDM are used as seals for connecting thin-walled stainless steel pipes and fittings. 11.4 Argon arc welding (butt welding) is used to join two pipes (or a pipe and a fitting) with DN(15-100) by performing circumferential T1G welding.

N2 should not be an extremely hazardous medium.

Why does the original poster say that N2 is a hazardous medium? Is it because high concentrations can cause suffocation? That can only happen in confined spaces, right? It’s not really a danger outdoors, generally speaking.

There is a DN15 pipeline in the factory area that is connected using threads; is this not in compliance with the specifications? ? Answer: The connection method should be determined based on pressure and the cross-sectional area of the pipe. Nitrogen is not considered a highly hazardous medium, and high-purity oxygen is also connected using threaded fittings. Gas cylinders for oxygen, nitrogen, hydrogen, argon, etc., all use threaded connections, and their maximum allowable pressure is 15.0 MPa. Therefore, the connection method must be designed and selected based on the cross-sectional area of the pipe.

If you accidentally inhale two breaths of N2, you will die instantly without any pain. The extremely hazardous substances mentioned in the regulations refer only to those with carcinogenic properties; so which one is more harmful?

In practical design, nitrogen is an extremely common medium; it is sufficient to follow the specifications for design, construction, and inspection.

It’s no big deal even if nitrogen leaks; your pipe is only DN15, so what’s there to worry about? Go ahead and use it without hesitation; focus on addressing the major issues, and ignore these minor problems.

But there should be no problem with the pipeline

According to GB50316, for fluids of categories A1 and A2, threaded sealing is only permitted for DN20 and smaller sizes, and weld sealing is required; no specific provisions exist for the other sizes, so threaded sealing should be acceptable