Abstract: Drilling hose is connected to undertake High Pressure manifolds pipe line between the sink and faucet, its connection to connect usually Union. Require special welding High pressure union between a high pressure hose and fittings require no welding distortion, welding seams, high load carrying capacity.
Drilling company machine repair brigade charged with two companies in the drilling, well outside the team's equipment maintenance and high-pressure pipeline welding and maintenance work, Drilling hose fittings due to its special material and joints become the key to this cycle path. High pressure union after prolonged use, the weld fracture in serious condition, mud, water, rust oil more, there is a big security risk, we must find the cause, to develop measures to reduce failure rates and lower labor costs.
1. Union Drilling hose and connecting parts and breakage Fracture
1.1. Drilling hose fittings and welding High pressure union
Because the material is the reason 35Mn high quality carbon structural steel, a key part of this cycle welding channel. After prolonged use, due to the high pressure mud circulation, drug resistance, strong vibration rig, welding personnel skill levels vary. So that the weld fracture in serious condition, there is a big security risk.
1.2 Weld cracking from the middle position shown in Figure (omitted)
1.3. The presence of a large number of defects in the weld
The inspection measurements to each of the connectors to the unit, the defect length distribution in Table 1.
Table 1 defect distribution

1.3.1 Defect Analysis
(1) Sidewall undercut
Ratio Sidewall undercut defects accounted for a larger, the measurement, Sidewall undercut depth> 0.5mm. And continuous Sidewall undercut. We know that there Sidewall undercut reduces the effective working area of ​​the weld, stress concentration occurs in the Sidewall undercut region, the formation of cracks, and gradually extended, and finally the structure was broken.
(2) lack of fusion, slag, crater cracks
Welders welding materials used for φ4mm the E4303 electrodes, welding current 130A. Such alkaline electrode welding slag viscosity ratio is small, slag mobility, use a small welding current, welding slag and iron tell, is likely to cause slag, lack of fusion, cracking defects. When Crater, craters are not filled, resulting crater cracks.
(3) lack of weld reinforcement
Weld fittings should be flush or slightly higher. To meet this requirement, at least four layers to be welded. To grasp the progress, when set on, connection point is not completely solid, welders welding start from one end and the other end has not been due to tack or tack weld length is shorter, welding a greater tensile stress, the end of the pull , the connecting member is connected with the Union gap increases, this time, only one weld seam, weld reinforcement is insufficient, causing cracking.
1.4. The welding material inappropriate choice
Hose is under dynamic loading conditions, should be used for 50-70MPa intensity level of E50 series electrodes. E4303 case of carbon steel electrode, drug skin is titanium calcium type, mainly for low-carbon steel, mild steel welding, it is anti-poor and cold crack crack, its poor ductility and toughness, resulting in low tensile strength weld in the base metal, weld cracking resulting from the middle.
1.5 in. Structural stiffness and welding sequence
Welding process can hear the sound of the weld fracture. Rigidity, the greater shrinkage during cooling weld metal by stress and deformation within the deformation rate should be increased.
1.6. Other
Connector size by drawing with no welding, Union quality does not meet the technical requirements. Some without welding skills training personnel are involved in welding work, resulting in a large number of welding defects.
2.High pressure union weldability analysis
2.1. 35Mn steel material element content (Table 2)
Table 2 35Mn steel element content

2.2.Analysis of 35Mn steel welding
When cold plastic deformation moderate machinability is acceptable but poor welding. Compared with 30Mn steel, high carbon content, has a higher strength, abrasion resistance and hardenability, but the plastic was slightly reduced, and there is a white point and thermal sensitivity and tendency to temper brittleness, easy to form quenching tendency to crack.
Analyze the above problems must be solved in several ways welding assembly, welding sequence, welding materials.
3. High pressure union assembly, tacking
Weldment degrees two-point positioning groove weld, the weld length positioning ≥20mm.
4. High pressure union welding sequence
4.1. The first root pass, the second the third renewal charge, fourth Daugai surface.
4.2. The welding parameters in Table 3.
Table 3 parameters

E5016 is a low-potassium type electrode, its mechanical properties than the chin calcium type electrode is good, especially the impact toughness far beyond Chin calcium type electrode, a strong anti-cracking ability, suitable for welding carbon steel and alloy steel structure vital structures. Dried before use to 350 ℃, for 2 hours, used with the check, when welding with short arc, to reduce pores. E5016 slag viscosity, molten slag lag the pool, the pool is easy to observe, not easy to produce slag. When the rod from side to side, both sides remain slightly and prevent Sidewall undercut. When using the reflow method Crater, fill the crater.
5. High pressure union welding operation
Reasonable welding sequence can effectively reduce the stiffness and deformation of the connection, you can press the following steps welding: groove preparation, tack welding, weld root (must be completed, so that the side welding molding), filling cover surface, natural cooling.
6.In conclusion
The above method of welding Drilling hose High pressure union of weld fracture, cracking reduced. Good effect, lower revision rate, reduce labor costs, to meet production needs. The above method is also suitable for drilling mud pressure manifold welding.