Improvement measures for large blind flange pressure operation of gas pipeline

The operation of the blind flange is essential for metallurgical enterprises in the process of equipment maintenance and emergency repair of gas systems and related processes, and the realization of efficient and safe operation of the blind flange is an important link to ensure the safe production of enterprises. By changing the original operation method, it can make the operators of blind flange save more physical strength, and the operation process is also smoother and safer, creating benefits for the enterprise.


Blind flange extraction plugging operation, is in the process of equipment repair or maintenance, so that the maintenance parts and dangerous media (gas, etc.) to reliably cut off, in order to ensure the safe and successful completion of the maintenance of a gas operation. In the process of pumping and plugging large blind flange with gas, the gas in the pipeline is high pressure flow, usually blind flange operations are taken to reduce the gas pressure in the pipeline to ensure safety measures, but in order to ensure the continuous production of gas users and the safety of the entire gas pipeline network system, the gas pressure must be maintained at more than 3000 Pa. This will ensure that neither the user’s production nor the operation of the safety blind flange can be achieved.

1. Original method

According to the habit over the years, the current method of operation with pressure blind flange is: from the upper part of the pipe down into the blind flange, when the blind flange is gradually inserted into the pipe, the pressure of the gas withstood also gradually increased, so that the blind flange of the card in the pipe, can not enter the bottom of the flange normally. In this way, in the process of blocking the blind flange operation, when the flange is opened, the gas from the flange a large number of leaks, if the security measures are not in place, will be ready to poisoning, fire, explosion and other accidents, threatening the lives of operators, and will cause serious consequences to the gas network and even the entire enterprise.

2. Improvement methods

With the development of metallurgical enterprises, the scale of production continues to expand, stop sending gas operations more and more frequently, pumping, plugging large blind flange operations more and more, with the previous method has been unable to meet the current needs of safety operations, so the method of plugging blind flange operations must be comprehensively improved. Now the gas pipeline with pressure plugging blind flange operation improvement methods are discussed. The operation method of plugging blind flange with gas: the blind flange will be lifted from the bottom of the pipe to the top, so that the blind flange smoothly into the flange.

2.1 Preparation work before operation

(1) Determine the operating position of the blind flange, understand the type of gas, gas flow direction.
(2) Check whether the gas pipe support bracket pipe bracket and gas pipe welding phenomenon, how the resistance, if there is welding phenomenon, to cut open, reduce the expansion resistance of the pipe.
(3) Remove the obstacles around the operation, and the bolts on the original flange should be replaced before the operation.
(4) Welding support iron 2-4 pairs on both sides of the flange, 400mm long, 200mm wide, support bars 350mm-400mm long, each pair of support iron spacing 350-400mm, support iron should have sufficient strength.
(5) Operation shelf and platform specifications: DN2400mm pipeline, for example, build two layers of shelves, the first layer from the bottom of the pipe 1-1.2m, the shelf width should be greater than 2m on both sides of the edge of the pipe, 3m long, the middle of the shelf plane to leave a gap of 150-200mm, in order to place the blind flange gasket; the second layer of shelves to build at the centerline on both sides of the pipe. Sloping ladder width of 1200mm, slope 30 ° angle, sloping ladder tied horizontal wooden bars; fence height of 1200mm, during which three layers of horizontal bars should be set.
(6) Spreader: Weld a gantry hanger on each side of the pipe above the corresponding flange, the hanger should be 1m above the top of the gas pipe, inclined to the outside at an angle of 45°, the vertical bar on one side of the hanger is welded to one end of the top horizontal bar, and the vertical bar on the other side is left in a slot so that the other end of the horizontal bar is stuck into the slot. The horizontal rod should be longer than the two vertical rods spacing of about 200-300mm, to avoid both sides are welded, the flange can not top open. As in Figure 1.
20230110000551 76048 - Improvement measures for large blind flange pressure operation of gas pipeline
Figure.1 Gantry hanger schematic diagram
(7) The size of the blind flange to determine: use the disk ruler to measure the perimeter of the pipe near the flange, while measuring the distance between the inner edge of the flange bolt hole and the outer wall of the pipe, the formula is as follows:

d = 0.31831s + 2h

In the formula:

  • d – the diameter of the blind flange.
  • s – the measurement of the outer circumference of the pipe.
  • h – bolt holes in the distance from the outer wall of the pipe.

(8) The production of blind flange, according to the calculated diameter of the blind flange for production, the blind flange in the center line up to 100mm, on each side of a shank, shank length 150mm, width 80mm, shank to leave a party hole, in the blind flange above the center line position set a shank, shank height of 300-350mm, width 150mm, and leave a square hole. With two 8 # iron wire in the blind flange side of the spot welding for two weeks, which outside a week close to the outer ring of the blind flange, inside a week to shrink 20-30mm, and use the oil pan root in the two circles of iron wire between the spread, with a thin wire stapled to the two circles of iron wire. As shown in Figure 2.
20230110001514 10859 - Improvement measures for large blind flange pressure operation of gas pipeline
Figure.2 Schematic diagram of blind flange
(9) In the top center line of the pipeline gas source flange side 500-600mm welding a pivot point, the height of the pivot point is 300mm, the pivot point should be firm, hang a 1t guide chain on the pivot point for backup.
(10) Hang a 2t guide chain on each gantry crane to lift the blind flange to the flange mouth.

2.2 Safety requirements during operation

  • (1) Before the operation, safety education is given to the participants, who are required to conduct a comprehensive inspection of the oxygen respirator and air breathing apparatus worn by each of them to ensure that they are good; the air breathing apparatus should be fully checked for pressure, and the oxygen respirator should be checked for positive and negative pressure, and wear good protective equipment.
  • (2) Grounding device, with copper conductors connected together on both sides of the flange of the operation (connected at the top of the pipe) whose resistance is approximately less than 0Ω, the insulation layer should be removed during installation to ensure good electrical conductivity.
  • (3) The outer side of the blind flange should be coated with yellow glycerin to prevent sparks from friction, the operation should use explosion-proof tools, the use of iron tools should be coated with oil.
  • (4) Alert the danger zone, the work site within a radius of 50m should be prohibited open fire (if it is coke oven gas operations, the alert site should also be expanded). Cut off the site near the power supply, heat sources, non-operators are prohibited to enter.
  • (5) Before separating the flange, to remove the iron oxide, dust and debris in the flange, to avoid the flange separated from the spray, into the eyes of the operator, affecting the operation.
  • (6) To ensure that the respirator pressure is sufficient during operation, to prevent touching off the mouthpiece box and nose clip when using the oxygen respirator, and the headband must be tied tightly when using the air respirator.
  • (7) When removing screws, pay attention to gas leakage and keep the four corner screws to prevent gas poisoning.
  • (8) Operation of the various positions of the operator, should put the tools and remove the bolts to prevent injuries from falling, the jack should be tied.
  • (9) Contact the pressure before the operation, the pressure gauge should be installed near the operation site, and the pressure should be watched during the operation, the normal operation of the gas users can not temporarily stop the furnace, and the hot air furnace can not be changed.

2.3 The operation steps of the blind flange operation

  • (1) Remove the screws, leave the four corner screws, should not leak gas shall prevail.
  • (2) Lower the pressure, organize by gas dispatch to lower the pressure of gas pipeline network and notify all users along the pipeline to pay attention to the gas pressure.
  • (3) Sound the alarm, alert the danger zone, guard all roads with guard ropes and have special guards, if there is a railroad, contact the transport department dispatch to close the road before operation.
  • (4) Hear the alarm, the operator wears a good respirator, remove the four corner screws, all the bolts below the radius of the pipe are withdrawn, the blind flange of the first lifting side, the screws are unloaded to 400mm below the radius, after the screws are all unloaded, the operation commander instructs the jack to separate the flange with a secret signal.
  • (5) Check the gas pipeline in the separation of the flange, whether there is a backlash, sinking and other phenomena, if there is a backlash or sinking phenomenon, the pipeline to add the top or the pipeline will be lifted.
  • (6) Observe when the flange gap can be inserted into the blind flange, stop the top jack, pull out the gasket, while clearing the flange on the debris.
  • (7) Lifting the blind flange, when hanging the blind flange, one side first, two blind flange shank tilt 30 °, the other side followed by lifting, first lifting one side of the blind flange shank, from the jack side up to the top of the jack.
  • (8) When the shank of the top of the blind flange out of the pipe, the top of the pipe fixed point of the guide chain hanging on the shank of the blind flange, pulling inward, the other side of the rear lifting while continuing to lift the blind flange upward until the blind flange into the flange.
  • (9) When the blind flange into the flange, the bottom of the pipe string on the bolt, check whether the blind flange of a week of the seal in place, back to the jack, tighten the bolt.

3. Conclusion

In summary, the improvement of the measures to reduce the physical exertion of the operator, shorten the operating time, reduce the chances of accidents, as long as adequate preparation before the operation, in the operation, carefully implement each work link, the method is feasible.
20230110001823 47346 - Improvement measures for large blind flange pressure operation of gas pipeline
Fig.3 Schematic diagram of the process of plugging the blind flange
The operation of blind flange of blast furnace gas DN2400mm and DN2800mm pipeline was carried out by the above method, which further confirmed the feasibility of the improved method.

Author: Ke Zhongnan

Source: China Blind Flange Manufacturer – Yaang Pipe Industry Co., Limited (

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