Repair and maintenance of kelly bar

Maintenance of kelly bar

Required inspection items	Intermediate kelly bar	Outermost and innermost kelly bar
First inspection	200±50hours	100±50hours
After that check the interval	500±100hours	250±50hours

Repair of common faults

- Transverse cracking of the weld at the kelly box

The cracks in the welds at the kelly box start from the surface and then expand gradually. When inspecting, just check if the cracks are visible to the naked eye.
Repair: For small cracks, just grind with an angle grinder until the crack disappears and then weld. For larger cracks, first use flame gas to cut the cracked area, then grind with an angle grinder until the crack disappears completely. The groove angle is about 50-60°, then weld and grind the weld surface to make it smooth.

Repair plan for kelly box fracture:
If the crack at the kelly box has seriously extended to the steel pipe mother body, or has broken, it is necessary to replace the kelly box short section. First, determine the specific cutting position based on the innermost layer length. Take φ470-4×20m kelly bar as an example:
1. Determine the specific cutting position according to the length of the accessory and the total length of the innermost rod:
The total length of the accessories is 1938mm: the total length of the fourth section of kelly bar is 21530mm, so the total length of the remaining part after cutting is 19592mm
2. Cut the gap according to the requirements of the diagram and polish it until the metallic luster is visible, and cut the key strip at the end of the kelly bar by 50-100mm, as shown in the figure below:

3. Butt the accessories with the cut kelly bar (use a ruler/profile to align the upper and lower key strips, and visually check that there is no obvious misalignment of the other key strips, and the misalignment is ≤ 2mm). After butt connection, the total length of the kelly bar is 21530mm, and the key strips are repaired and welded, as shown in the following figure:

Welding process requirements:

1. Use ER70-G (GB national standard) welding wire (AWS/American standard ER100S-G);
2. Preheat the groove and the 30mm range on both sides to 180-250°C before welding;
3. Use multi-layer and multi-pass welding, each pass is 3-4mm thick and ≤12mm wide;
4. Grind and clean impurities and spatter after each layer is welded (between layers);
5. Welding parameters: I (240±20A); U (28±2V);
6. The cover weld has a residual height of 0.5-2mm and is polished flat after welding.

- Key strip longitudinal weld cracking

When longitudinal cracks are found in the key bar weld, first grind the cracked area with an angle grinder to check whether the crack has seriously extended to the steel pipe matrix. If the crack has not extended to the steel pipe matrix or has slightly extended, just grind the crack with an angle grinder until the crack disappears completely, and then repair the weld. If the crack has seriously extended to the steel pipe matrix, the corresponding accessories need to be replaced.

Welding process requirements:

1. Use ER50-6 (GB national standard) welding wire (AWS/American standard ER100S-6);
2. Use multi-layer welding for welding, back-welding method (right welding method), front-end welding method (left welding method);
3. After back-welding (between layers), grind and clean impurities and spatter;
4. Welding parameters: I (240±20A); U (28±2V);
5. The overlapped part of the joint has a residual height of 0.5-3mm, and it should be polished flat after welding.

- Key strip transverse cracking

After discovering that the key bar has a transverse crack:
1)Use an angle grinder to grind slight cracks until the weld disappears and then weld it;
2)If the crack is large, first use flame cutting to cut the cracked area, then use an angle grinder to grind until the crack disappears completely and then weld it;
3)When the crack seriously extends to the steel pipe mother body, the accessories need to be replaced.

- The locking point and the corner of the support plate are cracked

The repair method for cracks at corners is the same as that for lateral cracks on the key strip.

Welding process requirements:

1. Use ER50-6 (GB national standard) welding wire (AWS/American standard ER100S-6);
2. Use multi-layer welding for welding, back-welding method (right welding method), front-end welding method (left welding method);
3. After back-welding (between layers), grind and clean impurities and spatter;
4. Welding parameters: I (240±20A); U (28±2V);
5. Use angle grinder + alloy grinding head to grind the corner height position for smooth transition (arc shape).

- Key strips, oblique keys and filler plate flashing and ridge raising

During the long-term use of key strips, oblique keys and filler plates, there will be flash and edges due to wear (see the figure below). If there are flash or edges > 2mm, they need to be polished, otherwise it may cause the rod to pull.

Repair: Use an angle grinder to smooth the edges.