Drilling and Production Machinery Repair Plant, Jianghan Petroleum Administration Bureau
The 2" swivel joint and phi 45 swivel joint in a 700 kg/cm2 fracturing manifold have a working pressure of 700 kg/cm2 and a test pressure of 900-1000 kg/cm2. During fracturing operation, high-pressure fracturing fluid carrying quartz sand flows through the inner bore of the swivel joint at very high velocity, causing severe wear on the outer-side bore wall at the bend and even wearing it through. If cast-steel blanks are used to manufacture this type of swivel joint, quality cannot be ensured. In the past, when our plant manufactured this type of swivel joint, a solid right-angle blank was first forged and then holes were drilled from both ends until they connected. This structure could not meet the operating conditions of a 700 kg/cm2 fracturing manifold. We now use a hot-bending and forging process to manufacture the swivel joint blank and ensure that the outer wall thickness at the bend is greater than the inner wall thickness. After machining and pressure testing, the blank can meet the specified technical requirements.
The manufacturing sequence for the forged swivel joint blank is: turning the through-bore blank, filling the inner bore with sand, heating, hot bending and forging, sand removal, and quenching and tempering. The following description uses a 2" swivel joint (Figure 1) as an example.
Figure 1. Blank drawing of a 2" swivel joint
Only the main dimensions are marked in the figure; dimensions in parentheses are finished-product dimensions.
1. Turning the Through-Bore Blank
When the through-bore blank is heated and bent, the outer wall of the bend is stretched and becomes thinner, while the inner wall becomes thicker. Therefore, the middle section of the blank is required to be turned eccentrically (Figure 2), so that the outer side of the formed swivel joint has sufficient thickness and the service life of the swivel joint is extended.
Figure 2. Through-bore blank
The length a in Figure 2 can be calculated according to the arc length of the centerline of the inner bore at the bend.
The eccentricity b in Figure 2 can be calculated according to the principle that the volume remains unchanged before and after hot bending.
The wall thickness on the inner side of the bend generally meets requirements after bending and does not need to be checked. This eccentric through-bore blank is turned on a lathe using an eccentric-sleeve fixture.
2. Filling the Inner Bore with Sand
To reduce deformation of the bend during hot bending, including flattening and diameter reduction, the inner bore of the blank must be filled with sand and compacted as much as possible. We use the sand-loading device shown in Figure 5 to fill the bore with relatively coarse quartz sand for cast steel, with a particle diameter of about 1-2 mm, after the sand has been pre-dried.
Sand-loading device
1. Welded frame;
2. 5-ton jack;
3. Plug;
4. Workpiece; 5. Sand; 6. Cover
Before filling with sand, cover 6 is tack-welded to one end of workpiece 4, and then sand is loaded into the inner bore of workpiece 4. After the sand is loaded, plug 3 is placed at the upper end of workpiece 4. Jack 2 is used to compact the sand, and finally plug 3 is tack-welded onto workpiece 4.
3. Heating
To reduce deformation resistance during hot bending, the blank is heated to 1000-1100 C. We use a crude-oil-fired forging heating furnace. While the blank is heated in the furnace, it should be turned at appropriate intervals so that it is heated uniformly and thoroughly.
4. Hot Bending and Forging
Because our plant does not have special hot-bending equipment, the tool shown in Figure 6 is used for hot bending.
The bore diameter of inner sleeve 6 in fixture 1 is determined according to the workpiece size. The heated through-bore blank is first inserted into the bore of inner sleeve 6 in fixture 1. At this time, attention must be paid to aligning the eccentric direction so that the side with greater wall thickness is located on the outer side of the bend. Then handle plate 4 is used to bend the blank. After bending, the bend section of the blank will show slight flattening. The correcting die shown in Figure 7 can be used to forge and correct it on a 560 kg forging hammer. The entire hot-bending and correction process is completed in one heat. A 90 degree template is used for inspection to ensure that the angle is within 90 degrees plus or minus 8 degrees.
Correcting die
Hot-bending tool
1. Fixture; 2. Fixed plate frame; 3. Lower anvil of 560 kg forging hammer; 4. Handle plate; 5. Workpiece; 6. Inner sleeve
5. Sand Removal and Quenching and Tempering
The covers and plugs at both ends of the blank are opened with a chisel, and the sand is poured out; the sand can be reused. Because the machining allowance of the blank is not large, the blank is directly quenched and tempered without rough machining. This reduces the number of times the swivel joint must be clamped during machining and avoids difficulty in alignment. At present, the main problems of this process are: 1. the blank is bent manually during hot bending, resulting in high labor intensity and low efficiency; 2. the eccentric direction must be aligned during hot bending.
