Adjustable high-pressure heater U-shaped pipe pressing device
By designing an adjustable high-pressure heater U-tube pressure testing device, and adopting a detachable height adjustment plate and an independent pressure monitoring valve, the safety hazards and compatibility issues of traditional devices are solved, and efficient and safe testing of multi-specification U-tubes is achieved.
Patent Information
- Application Number
- CN202520850579.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-30
- Publication Date
- 2026-01-06
- Estimated Expiration
- 2035-04-30
AI Technical Summary
Traditional U-tube pressure testing devices pose safety hazards and can leak due to their inability to securely tighten the tubes, and they are not compatible with U-tubes of various bending radii.
An adjustable high-pressure heater U-tube pressurization device was designed. It uses a detachable height adjustment plate to adjust the distance between the upper and lower saddles, combined with independent pressure monitoring and safety valve ports. It is welded to the U-tube through a transverse connecting pipe to avoid the phenomenon of plug flying out and water leakage. It is compatible with U-tubes of various specifications of bending radius.
It improves the safety and adaptability of the pressure testing device, reduces material costs, and increases testing efficiency. It is suitable for U-shaped tubes with multiple bending radii and meets the requirements for high-parameter testing.
Smart Images
Figure CN223769729U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of pressure vessel testing technology, and in particular relates to an adjustable high-pressure heater U-tube pressure testing device. Background Technology
[0002] Traditional U-tube pressure testing fixtures typically employ structures such as expansion plugs and fixing clamps. During pressure testing, the expansion plug can easily fly out like a bullet, rebounding after impacting walls or other objects, posing a significant risk of injury. While fixing clamps avoid this risk, slight ellipticing at the ends of the heat exchange tubes often prevents them from securing properly, leading to leaks and hindering normal pressure increase. In such cases, an expansion plug structure is often necessary as a remedy. Therefore, the structure of the high-pressure heater U-tube pressure testing device requires further improvement to enhance its performance. Furthermore, a design that can adapt to pressure testing of U-tubes with various bending radii would be considered a better structural design. Utility Model Content
[0003] This utility model addresses the aforementioned problems by providing an adjustable high-pressure heater U-tube pressurization device that offers good performance and can be adapted to U-tubes with various bending radii.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: the present invention includes an upper cylinder 2 and a lower cylinder 11 arranged horizontally, characterized in that upper caps 4 are provided at both ends of the upper cylinder 2, and lower caps 12 are provided at both ends of the lower cylinder 11; a first-side upper saddle 5 is provided at the lower end of the first side of the upper cylinder 2, and a second-side upper saddle 6 is provided at the lower end of the second side of the upper cylinder 2; a first-side lower saddle 3 is provided at the lower end of the first side of the lower cylinder 11, and a second-side lower saddle 1 is provided at the lower end of the second side of the lower cylinder 11; the first-side upper saddle 5 and the first-side lower saddle 3 are connected to a first-side detachable height adjustment plate 7 by first-side fasteners; the second-side upper saddle 6 and the second-side lower saddle 1 are connected to a second-side detachable height adjustment plate 23 by second-side fasteners.
[0005] A water inlet N1 is provided on the lower pipe cap 12 on the first side of the lower cylinder 11, and a water outlet N2 is provided on the lower pipe cap on the second side of the lower cylinder 11; a pressure monitoring port N3 is provided on the upper end of the first side of the upper cylinder 2, and a safety valve port N4 is provided on the upper end of the second side of the upper cylinder 2.
[0006] The wall of the upper cylinder 2 is connected to the inner end of the transverse upper connecting pipe (N5b~N14b), the outer end of the upper connecting pipe (N5b~N14b) is the upper welded connection end of the U-shaped tube 10 to be tested, and the upper connecting pipe (N5b~N14b) is connected to the inside of the upper cylinder 2.
[0007] The wall of the lower cylinder 11 is connected to the inner end of the transverse lower connecting pipe (N5a~N14a), the outer end of the lower connecting pipe (N5a~N14a) is the lower welded connection end of the U-shaped tube 10 to be tested, and the lower connecting pipe (N5a~N14a) is connected to the inside of the lower cylinder 11.
[0008] As a preferred embodiment, the combination of the upper connecting pipe (N5b~N14b) and the lower connecting pipe (N5a~N14a) of this utility model is in multiple sets, and the multiple sets of upper connecting pipe (N5b~N14b) and lower connecting pipe (N5a~N14a) are evenly distributed along the length direction of the upper cylinder 2 and the lower cylinder 11.
[0009] As another preferred embodiment, the inner end of the upper connecting pipe (N5b~N14b) is welded to the wall of the upper cylinder 2, and the outer end of the upper connecting pipe (N5b~N14b) is welded to the upper end of the U-shaped tube 10 to be tested; the inner end of the lower connecting pipe (N5a~N14a) is welded to the wall of the lower cylinder 11, and the outer end of the lower connecting pipe (N5a~N14a) is welded to the lower end of the U-shaped tube 10 to be tested.
[0010] As another preferred embodiment, the upper cylinder 2 and the lower cylinder 11 of this utility model are made of seamless steel pipes with a diameter of Φ76×6mm and a length of 1000mm, and the material is 20 steel.
[0011] As another preferred embodiment, the upper cap 4 of this utility model is welded to the upper cylinder 2, and the lower cap 12 is welded to the lower cylinder 11.
[0012] As another preferred embodiment, the upper middle part of the first side upper saddle 5 of this utility model is provided with a first side upper saddle arc groove 13 corresponding to the lower part of the upper cylinder 2, and the lower part of the upper cylinder 2 is welded into the first side upper saddle arc groove 13; the upper middle part of the first side lower saddle 3 is provided with a first side lower saddle arc groove 14 corresponding to the lower part of the lower cylinder 11, and the lower part of the lower cylinder 11 is welded into the first side lower saddle arc groove 14.
[0013] As another preferred embodiment, the upper middle part of the second side upper saddle 6 of this utility model is provided with a second side upper saddle arc groove corresponding to the lower part of the upper cylinder 2, and the lower part of the upper cylinder 2 is welded into the second side upper saddle arc groove; the upper middle part of the second side lower saddle 1 is provided with a second side lower saddle arc groove corresponding to the lower part of the lower cylinder 11, and the lower part of the lower cylinder 11 is welded into the second side lower saddle arc groove.
[0014] As another preferred embodiment, the pressure monitoring port N3 of this invention is connected to the pressure gauge 16 via the pressure monitoring valve 15.
[0015] As another preferred embodiment, a water outlet valve 17 is provided at the water outlet N2 of this utility model.
[0016] As another preferred embodiment, the first lower saddle 3 base plate of the present invention is provided with a first lower saddle connecting hole 18, and the second lower saddle 1 base plate is provided with a second lower saddle connecting hole 19, the second lower saddle connecting hole 19 being an elliptical hole.
[0017] As another preferred embodiment, the first side detachable height adjustment plate 7 and the second side detachable height adjustment plate 23 of this utility model are vertical strip plates, with a lower saddle connecting hole 8 at the bottom and an upper saddle connecting hole 9 at the top.
[0018] Secondly, the upper saddle connecting hole 9 described in this utility model is a vertical strip-shaped hole.
[0019] In addition, the lower saddle connecting hole 8 of this utility model is two, arranged vertically.
[0020] The beneficial effects of this utility model.
[0021] This utility model uses a detachable height adjustment plate to adjust the distance between the upper and lower saddles (equivalent to adjusting the distance between the horizontal upper connecting pipe (N5b~N14b) and the horizontal lower connecting pipe (N5a~N14a)), which can be adapted to U-shaped pipes 10 with multiple specifications of bending radius, thus improving the adaptability range.
[0022] This invention features a pressure monitoring port N3 and a safety valve port N4, providing both pressure monitoring and safety protection functions. Furthermore, the pressure monitoring port N3 and the safety valve port N4 employ independent interface layouts to prevent water flow disturbances from affecting measurement accuracy and ensure a short safety response time.
[0023] The horizontal upper connecting pipe (N5b~N14b) and the horizontal lower connecting pipe (N5a~N14a) of this utility model are connected to the U-shaped tube 10 to be tested by welding; this avoids the situation where the expansion plug flies out in the existing expansion plug pressure method, and also avoids the situation where the connection end of the heat exchange tube (U-shaped tube 10) is prone to water leakage in the existing fixed clamp pressure method. Attached Figure Description
[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The scope of protection of the present invention is not limited to the following description.
[0025] Figure 1 This is a schematic diagram of the structure of this utility model.
[0026] Figure 2 This is a side view of the present invention.
[0027] Figure 3 yes Figure 1 The AA cross-sectional view is connected to a U-shaped pipe.
[0028] Figure 4 yes Figure 1 BB cross-sectional view.
[0029] Figure 5 This is a schematic diagram of the detachable height-adjustable plate structure of this utility model. Detailed Implementation
[0030] As shown in the figure, this utility model includes an upper cylinder 2 and a lower cylinder 11 arranged horizontally. The upper cylinder 2 is provided with upper tube caps 4 at both ends, and the lower cylinder 11 is provided with lower tube caps 12 at both ends. A first-side upper saddle 5 is provided at the lower end of the first side of the upper cylinder 2, and a second-side upper saddle 6 is provided at the lower end of the second side of the upper cylinder 2. A first-side lower saddle 3 is provided at the lower end of the first side of the lower cylinder 11, and a second-side lower saddle 1 is provided at the lower end of the second side of the lower cylinder 11. The first-side upper saddle 5 and the first-side lower saddle 3 are connected to a first-side detachable height adjustment plate 7 by a first-side fastener. The second-side upper saddle 6 and the second-side lower saddle 1 are connected to a second-side detachable height adjustment plate 23 by a second-side fastener.
[0031] A water inlet N1 is provided on the lower pipe cap 12 on the first side of the lower cylinder 11, and a water outlet N2 is provided on the lower pipe cap 12 on the second side of the lower cylinder 11; a pressure monitoring port N3 is provided on the upper end of the first side of the upper cylinder 2, and a safety valve port N4 is provided on the upper end of the second side of the upper cylinder 2.
[0032] The wall of the upper cylinder 2 is connected to the inner end of the transverse upper connecting pipe (N5b~N14b), the outer end of the upper connecting pipe (N5b~N14b) is the upper welded connection end of the U-shaped tube 10 to be tested, and the upper connecting pipe (N5b~N14b) is connected to the inside of the upper cylinder 2.
[0033] The wall of the lower cylinder 11 is connected to the inner end of the transverse lower connecting pipe (N5a~N14a), the outer end of the lower connecting pipe (N5a~N14a) is the lower welded connection end of the U-shaped tube 10 to be tested, and the lower connecting pipe (N5a~N14a) is connected to the inside of the lower cylinder 11.
[0034] The inlet N1 is connected to an external high-pressure water pump, the outlet N2 is used for pressure relief and drainage after testing, and the pressure monitoring port N3 can display and monitor pressure changes in real time. The safety valve port N4 can be equipped with an A48Y-420 safety valve, which automatically releases pressure in case of overpressure, providing an extra layer of protection for safe production on site.
[0035] Pressure testing: Inject high-pressure water into the inlet N1 to the pressure required by the drawing. During the pressure holding period, observe the leakage through the pressure gauge at the pressure monitoring port N3 and the safety valve at the safety valve port N4 to ensure that the pressure is controllable.
[0036] Drainage: After the U-shaped pipe 10 passes the pressure test, drain and release pressure through outlet N2.
[0037] The upper connecting pipe (N5b~N14b) and the lower connecting pipe (N5a~N14a) are combined in multiple sets, and the multiple sets of upper connecting pipe (N5b~N14b) and lower connecting pipe (N5a~N14a) are evenly distributed along the length direction of the upper cylinder 2 and the lower cylinder 11.
[0038] By using multiple sets of upper connecting pipes (N5b~N14b) and lower connecting pipes (N5a~N14a), multiple U-shaped tubes 10 can be pressure tested at the same time, resulting in high pressure testing efficiency.
[0039] The inner end of the upper connecting pipe (N5b~N14b) is welded to the wall of the upper cylinder 2, and the outer end of the upper connecting pipe (N5b~N14b) is welded to the upper end of the U-shaped tube 10 to be tested; the inner end of the lower connecting pipe (N5a~N14a) is welded to the wall of the lower cylinder 11, and the outer end of the lower connecting pipe (N5a~N14a) is welded to the lower end of the U-shaped tube 10 to be tested.
[0040] The connecting pipe is welded to the end of the U-shaped tube 10 to be tested through a full-penetration weld structure to form a closed detection circuit, which conforms to the HG / T20583-2020 standard.
[0041] The upper cylinder 2 and the lower cylinder 11 are made of Φ76×6mm seamless steel pipes with a length of 1000mm and the material is 20 steel.
[0042] The upper cap 4 is welded to the upper cylinder 2, and the lower cap 12 is welded to the lower cylinder 11. The caps and cylinders are welded together to form a sealed cavity.
[0043] The upper middle part of the first side upper saddle 5 is provided with a first side upper saddle arc groove 13 corresponding to the lower part of the upper cylinder 2, and the lower part of the upper cylinder 2 is welded into the first side upper saddle arc groove 13; the upper middle part of the first side lower saddle 3 is provided with a first side lower saddle arc groove 14 corresponding to the lower part of the lower cylinder 11, and the lower part of the lower cylinder 11 is welded into the first side lower saddle arc groove 14.
[0044] The upper middle part of the second side upper saddle 6 is provided with a second side upper saddle arc groove corresponding to the lower part of the upper cylinder 2, and the lower part of the upper cylinder 2 is welded into the second side upper saddle arc groove; the upper middle part of the second side lower saddle 1 is provided with a second side lower saddle arc groove corresponding to the lower part of the lower cylinder 11, and the lower part of the lower cylinder 11 is welded into the second side lower saddle arc groove.
[0045] The first side upper saddle 5 and the second side upper saddle 6 are mirror images of each other and serve as supports.
[0046] The first side lower saddle 3 and the second side lower saddle 1 are mirror images of each other, except for the bottom plate connection hole (the second side lower saddle connection hole 19 is an elliptical hole).
[0047] The pressure monitoring port N3 is connected to the pressure gauge 16 via the pressure monitoring valve 15. A pressure gauge buffer tube 22 can be installed between the pressure monitoring valve 15 and the pressure gauge 16 to prevent damage to the pressure gauge 16 when water pressure is applied.
[0048] Pressure gauge 16 and safety valve adopt an independent interface layout to avoid water flow disturbance affecting measurement accuracy, and the safety response time is ≤0.5 seconds.
[0049] A water outlet valve 17 is installed at the water outlet N2.
[0050] like Figure 4 As shown, the first side lower saddle 3 base plate is provided with a first side lower saddle connecting hole 18, and the second side lower saddle 1 base plate is provided with a second side lower saddle connecting hole 19. The second side lower saddle connecting hole 19 is an elliptical hole. The elliptical hole can avoid the inaccurate alignment of the upper and lower circular connecting holes due to tolerance reasons, which would cause inconvenience in installation.
[0051] A saddle web 24 and a saddle stiffener 25 can be provided on the lower saddle base plate. The saddle web 24 is provided with a connection hole for a detachable height adjustment plate, and the saddle stiffener 25 supports the saddle arc groove.
[0052] The first detachable height adjustment plate 7 and the second detachable height adjustment plate 23 are vertical strip plates. The lower part of the vertical strip plate is provided with a lower saddle connecting hole 8, and the upper part of the vertical strip plate is provided with an upper saddle connecting hole 9.
[0053] The upper saddle connecting hole 9 is a vertical strip-shaped hole; it facilitates adjusting the connection position between the upper saddle (5, 6) and the detachable height adjustment plate.
[0054] The lower saddle connecting hole 8 is two in number and is arranged vertically.
[0055] like Figure 2 As shown, there are two detachable height adjustment plates 7 and 23 on the first and second sides, respectively, which are installed on both sides of the saddle.
[0056] Removable height adjustment plates (7, 23) with heights of 500mm, 1000mm, and 1500mm can be set respectively. The material of the removable height adjustment plates (7, 23) can be Q235B. Depending on the actual radius range of the U-shaped tube, by replacing the removable height adjustment plates (7, 23) of different heights, the distance between the upper and lower saddles can be adjusted to adapt to U-shaped tubes in the range of R50mm to R600mm. It is also possible to set only the highest removable height adjustment plate (7, 23), but this is not very convenient to use when the bending radius of the U-shaped tube being tested is very small.
[0057] The working process of this utility model will be described below with reference to the accompanying drawings.
[0058] Select a detachable height adjustment plate (7, 23) of appropriate height according to the bending diameter of the U-shaped tube 10 to be tested.
[0059] (1) First, tighten the lower bolts 20 of the detachable height adjustment plate (7, 23) and the lower saddle (1, 3) (the lower cylinder 11 and the lower saddle are a whole). The lower bolts 20 pass through the lower saddle connecting hole 8. Adjust the vertical position of the upper saddle (5, 6) (the upper cylinder 2 and the upper saddle are a whole), and then tighten the upper bolts 21 of the detachable height adjustment plate (7, 23) and the upper saddle (5, 6) to fix the pressure fixture. The upper bolts 21 pass through the upper saddle connecting hole 9.
[0060] (2) Weld the two ends of the U-shaped tube 10 to be tested to the outer ends of the horizontal upper connecting pipe (N5b~N14b) and the horizontal lower connecting pipe (N5a~N14a). Arc welding can be used. Ten U-shaped tubes 10 (heat exchange tubes) to be tested can be welded for each water pressure test.
[0061] (3) According to the normal water pressure test time, after the test is qualified, remove the heat-affected zone of the weld (removing the heat-affected zone of the weld is conventional knowledge for those skilled in the art), cut off the U-shaped pipe 10, so that the U-shaped pipe 10 is separated from the horizontal upper connecting pipe (N5b~N14b) and the horizontal lower connecting pipe (N5a~N14a), and the water pressure test of the ten U-shaped pipes 10 is completed.
[0062] (4) Generally, there will be a lot of heat exchange tubes in the same group (with the same bending diameter). Repeat the sequence (2) and (3) of the same group of U-shaped heat exchange tubes until all water pressure tests are completed.
[0063] After completing the same type (same bending diameter), loosen the upper bolt 21 and adjust the vertical position of the upper saddle (5, 6) (equivalent to adjusting the distance D between the horizontal upper connecting pipe (N5b~N14b) and the horizontal lower connecting pipe (N5a~N14a), where the distance D is as follows: Figure 3 As shown), satisfy the bending diameter of the next set of U-tubes 10, then tighten the upper bolt 21, and repeat the sequential steps (1) to (4) to carry out the water pressure test of the next set of U-tubes 10.
[0064] Example: When testing a U-shaped tube 10 with a diameter of Φ16×3mm and a bending diameter of 604mm, a 1000mm high detachable height adjustment plate (7, 23) is selected and installed between the upper and lower saddles. The two ends of the U-shaped tube 10 are welded to the upper horizontal connecting pipe (N5b~N14b) and the lower horizontal connecting pipe (N5a~N14a) respectively (up to 10 heat exchangers can be welded and tested at the same time). The pressure is increased to the pressure resistance test pressure required by the drawing and held for ≥10 seconds. If there is no leakage, no visible deformation and abnormal sound, it is considered qualified.
[0065] The safety of this device is significantly improved compared to traditional tooling, the material cost is reduced by more than 60% and it can be reused multiple times. The maximum pressure resistance reaches 60MPa, and it can be widely used for the testing of high-parameter heat exchange tubes in nuclear power, thermal power and other fields.
[0066] It is understood that the above specific description of this utility model is only used to illustrate this utility model and is not limited to the technical solutions described in the embodiments of this utility model. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to this utility model to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of this utility model.
Claims
1. An adjustable high-pressure heater U-tube pressing device, comprising a transversely arranged upper cylinder (2) and a lower cylinder (11), characterized in that The upper cylinder (2) is provided with upper pipe caps (4) at both ends, and the lower cylinder (11) is provided with lower pipe caps (12) at both ends; the first side upper saddle (5) is arranged at the first side lower end of the upper cylinder (2), and the second side upper saddle (6) is arranged at the second side lower end of the upper cylinder (2); the first side lower saddle (3) is arranged at the first side lower end of the lower cylinder (11), and the second side lower saddle (1) is arranged at the second side lower end of the lower cylinder (11); the first side upper saddle (5) and the first side lower saddle (3) are connected with the first side detachable height adjusting plate (7) through the first side fastener; the second side upper saddle (6) and the second side lower saddle (1) are connected with the second side detachable height adjusting plate (23) through the second side fastener; The lower pipe cap (12) of the first side of the lower cylinder (11) is provided with a water inlet (N1), and the lower pipe cap of the second side of the lower cylinder (11) is provided with a water outlet (N2); the first side upper end of the upper cylinder (2) is provided with a pressure monitoring port (N3), and the second side upper end of the upper cylinder (2) is provided with a safety valve port (N4); The wall of the upper cylinder (2) is connected with the inner end of the transverse upper connecting pipe (N5b-N14b), the outer end of the upper connecting pipe (N5b-N14b) is the upper welded connecting end of the U-shaped pipe (10) to be measured, and the upper connecting pipe (N5b-N14b) is in communication with the inside of the upper cylinder (2). The wall of the lower cylinder (11) is connected with the inner end of the transverse lower connecting pipe (N5a-N14a), the outer end of the lower connecting pipe (N5a-N14a) is the lower welded connecting end of the U-shaped pipe (10) to be measured, and the lower connecting pipe (N5a-N14a) is in communication with the inside of the lower cylinder (11).
2. The adjustable high-pressure heater U-tube pressing device according to claim 1, characterized in that The combination of the upper connecting pipe (N5b-N14b) and the lower connecting pipe (N5a-N14a) is multiple groups, and the multiple groups of upper connecting pipes (N5b-N14b) and lower connecting pipes (N5a-N14a) are uniformly distributed along the length direction of the upper cylinder (2) and the lower cylinder (11).
3. The adjustable high pressure heater U-tube bumping device of claim 1, wherein The inner end of the upper connecting pipe (N5b-N14b) is welded with the wall of the upper cylinder (2), and the outer end of the upper connecting pipe (N5b-N14b) is welded with the upper end of the U-shaped pipe (10) to be measured; the inner end of the lower connecting pipe (N5a-N14a) is welded with the wall of the lower cylinder (11), and the outer end of the lower connecting pipe (N5a-N14a) is welded with the lower end of the U-shaped pipe (10) to be measured.
4. The adjustable high-pressure heater U-tube pressing device of claim 1, wherein The upper pipe cap (4) is welded with the upper cylinder (2), and the lower pipe cap (12) is welded with the lower cylinder (11).
5. The adjustable high pressure heater U-tube bumping device of claim 1, wherein The first side upper saddle (5) is provided with a first side upper saddle arc-shaped groove (13) in the middle of the upper end corresponding to the lower part of the upper cylinder (2), and the lower part of the upper cylinder (2) is welded in the first side upper saddle arc-shaped groove (13); the first side lower saddle (3) is provided with a first side lower saddle arc-shaped groove (14) in the middle of the upper end corresponding to the lower part of the lower cylinder (11), and the lower part of the lower cylinder (11) is welded in the first side lower saddle arc-shaped groove (14).
6. The adjustable high pressure heater U-tube bumping device of claim 1, wherein The upper end middle part of the second side upper saddle (6) is provided with a second side upper saddle arc-shaped slot corresponding to the lower part of the upper barrel (2), and the lower part of the upper barrel (2) is welded in the second side upper saddle arc-shaped slot.
7. The adjustable high-pressure heater U-tube pressing device of claim 1, wherein A water outlet valve (17) is arranged at the water outlet (N2).
8. The adjustable high pressure heater U-tube bumping device of claim 1, wherein An first side lower saddle connecting hole (18) is arranged on the bottom plate of the first side lower saddle (3), and a second side lower saddle connecting hole (19) is arranged on the bottom plate of the second side lower saddle (1), and the second side lower saddle connecting hole (19) is an oval hole.
9. The adjustable high pressure heater U-tube bumping device of claim 1, wherein The first side detachable height adjusting plate (7) and the second side detachable height adjusting plate (23) are vertical strip-shaped plates, the lower part of the vertical strip-shaped plate is provided with a lower saddle connecting hole (8), and the upper part of the vertical strip-shaped plate is provided with an upper saddle connecting hole (9).
10. The adjustable high pressure heater U-tube bumping device of claim 9, wherein The upper saddle connecting hole (9) is a vertical strip-shaped hole.