In urban thermal pipe networks and industrial steam pipes, there is a magical device known as the "pipe yogi". It does not occupy a huge footprint like a square compensator, nor is it as sensitive to corrosion as a corrugated compensator, but rather resolves the huge stresses caused by the thermal expansion of the pipe through an elegant rotational motion. It is the rotational compensator. This paper will systematically analyze the technical knowledge of rotary compensator from working principle, advantages and characteristics to installation specification.

I. What is a rotational compensator?

Rotary compensator is a new type of compensator for thermal expansion of thermal pipeline. Its structure is mainly composed of integral sealing seat, sealing gland, large and small heads, anti-friction centering bearing, sealing material, rotating cylinder and other components。 It is not used alone, but requires two or more groups to form a group, and is mounted on the thermal pipe to form relative rotation, so as to absorb the thermal displacement of the pipe and reduce the pipe stress。

For example, the traditional natural compensation method (such as the π-shaped elbow) is like letting the pipe "twist" by itself to absorb the thermal stress, while the rotary compensator installs a precise "rotary joint" for the pipe, which converts the axial thrust into rotational motion about the axis, thus dispersing the concentrated stress into a moment that is uniformly borne by the whole structure。

2. Working principle of rotary compensator

To understand the working principle of rotary compensator, we can start with the concept of "force couple". The pair of forces of equal magnitude and opposite direction are rotated around the center of Z axis by the force arms to absorb the heat expansion generated on the heat pipes on both sides of the force couple。

When the pipe expands under heat, the generated axial thrust does not directly resist the compensator, but is directed into a system of rotating barrels and L-shaped force arms arranged in pairs. This system converts thrust into rotational motion, allowing the pipe to naturally release thermal stress like "stretching" rather than destructively squeezing the pipe wall。

This design strategy of changing passive bearing to active guidance gives the rotary compensator strong compensation ability and extremely high reliability.

3. Core advantages of rotary compensator

1. Large amount of compensation and long coverage distance

One of the greatest advantages of a rotary compensator is its amazing compensating ability. The largest set of compensators can compensate 500m pipe section, far exceeding the traditional compensators。 On long-distance linear pipelines, one set of rotary compensators can replace multiple sets of traditional compensators, which greatly simplifies the design of pipeline network.

2. No blind plate force, small fixing bracket

This is the most significant advantage of the rotary compensator compared with the axial corrugated compensator. Since the compensator does not generate the blind plate force (or inward pressure) generated by the medium pressure, the fixing brackets at both ends of the compensator can be made very small。 This feature is particularly suitable for large-diameter pipelines, which can greatly reduce civil construction investment.

The traditional axial corrugated compensator will produce huge blind plate force when working, which needs an extra firm fixed bracket to bear; However, the rotary compensator fundamentally eliminates this thrust, and the advantage of engineering economy is obvious.

3. Superior sealing performance and long life

The rotary compensator adopts advanced sealing materials such as flexible graphite, which has the characteristics of high self-lubricating performance, small friction coefficient, corrosion resistance and good airtightness。 Under normal conditions, it will not leak after 20 years of use。 Even if there is an individual dripping phenomenon, only slightly tighten the spring to tighten the flange bolt can stop the leakage, and the maintenance is extremely simple.

4. Water hammer resistance, corrosion resistance, high safety

Unlike the corrugated compensator, the rotary compensator has a strong structure, is insensitive to chloride ions, is not affected by stress corrosion, and can withstand water hammer impact。 This is especially important in steam pipelines – water hammers are a common cause of bursting corrugated compensators, and the rigid construction of rotary compensators makes it effective against this risk.

5. Small pressure loss and good energy-saving effect

The design of the rotary compensator avoids the sudden change of the medium flow channel, the pressure loss is small during operation, and the influence on steam transport is small。 This means lower energy consumption and higher delivery efficiency.

6. Convenient heat preservation, small heat loss

Since the compensator does not have to leave the amount of thermal extension and contraction during heat preservation, the heat loss is small。 At the same time, its regular shape is also convenient for the construction of insulation layer.

4. Comparison between Rotary Compensator and Other Compensators

For a clearer picture of the positioning of a rotary compensator, the following table contrasts it with several common compensators:

V. Selection and installation points of rotary compensator

1. Precautions for model selection

When selecting a rotary compensator, the following points should be paid attention to:

• Supply method: π-shaped combination is not for the whole group, only for a single rotary compensator; Omega-shaped combinations are available for whole groups and single units
• Parameters provided: The diameter, working pressure and temperature must be indicated when ordering
• Non-standard combination: Parameters such as arm length, H value and compensation ability should be indicated

2. Inspection before installation

Before installation, check the model, specification and pipe configuration of the compensator, which must meet the design requirements。 Check if the outer end of the inner tube exposes the gland to ensure that the design requirements are met。

3. Direction and Pre-Offset

• Confirmation of flow direction: Install according to the indication of media flow direction specified by the compensator
• Pre-bias installation: Half of the rotation angle θ shall be pre-biased, or △ Half of L is pre-biased
• Concentricity: The rotary compensator remains concentric with the pipe

4. Stent Configuration

There shall be a reliable guide support at the appropriate position near the two ends of the rotary compensator to ensure free expansion and contraction during operation。 The safety margin shall be added to the pipe bracket according to the expansion amount, and the operating temperature and installation temperature shall be appropriately considered。

5. Welding and Protection

• Weld (or flange) the rotary compensator directly to the pipe, and apply a shield to protect the compensator during welding
• End pipe welding shall comply with the provisions of GB985-88 and GB986-88
• When welding in severe cold season, the end of steel pipe and end pipe should be preheated

6. Hydraulic test

After installation, check whether the gland bolts are uniformly tightened (not too tight, as long as they are uniform), and then carry out the segmented hydraulic seal test。 The test shall be conducted in three division:

• Boost the pressure to 1/3 of the working pressure for the first time, and observe whether there is dripping phenomenon
• Second boost to working pressure, check for leakage
• For the third time, the pressure is increased to 1.5 times the working pressure for 10min. If the pressure is unchanged, the strength test is qualified; After the pressure drops to the working pressure for 30min, if the pressure remains unchanged, the sealing performance is qualified

7. Operation maintenance and heat preservation

• Pay attention to check the sealing state after operation. Under normal circumstances, it is maintenance-free for 20 years
• The thermal insulation protection structure of the compensator is the same as that of the pipe, but no binding force can be exerted on the telescopic part of the telescopic pipe
• The compensator can be installed at various ambient temperatures according to the installation length LMax without stretching or compressing

Scope of Application and Application Prospects

The rotary compensator can be installed on the steam buried pipe and the hot water buried pipe, which can save a lot of investment and improve the operation safety。 It is especially suitable for heat network projects in industrial areas or urban suburbs, especially in scenarios with long straight-line distances of pipelines。

In recent years, Chinese enterprises have been at the forefront of the world in the field of rotary compensators. The enterprises represented by Jiangsu Beite have filled many domestic gaps in their rotary compensator technology, obtained invention patents in the United States, the European Union and other countries and regions, and their products have been used in major projects such as Sinopec, PetroChina, Beijing Daxing Airport and Winter Olympics。 At present, a complete rotary compensator industry chain has been formed in China, which has completely changed the pattern of European and American enterprises occupying the high end of the value chain for a long time。

sum up

Rotary compensator is an important innovation in thermal pipeline compensation technology, and its core advantages can be summarized in the following table:

The rotary compensator is especially suitable for long-distance linear pipeline heating network engineering, and has comprehensive advantages in compensation capacity, safety and economy. A rotary compensator system with reasonable design and standard installation can run stably for a long time under high temperature and high pressure conditions, and provide a reliable "rotary joint" for the heating pipe network.