Shale Gas Cementing Ultra-High Pressure Cement Head
Recently, the company undertook an ultra-high pressure cement head for welding shale gas cementing. The working pressure on the site reached 70 MPa and the test pressure required to reach 100 MPa. It is an ultra-high pressure vessel. After discussion, it was determined that the 35CrMo low-alloy high-strength steel pipe after quenching and tempering was selected as the welding cylinder, and five products were prepared by inserting the enamel (material 35CrMo) into the cylinder.
The chemical composition and mechanical properties of 35CrMo steel are shown in Tables 1 and 2. 35CrMo seamless pipe has high static strength, impact toughness and high fatigue limit. It has high creep strength and long-lasting strength at high temperature and moderate plasticity in cold deformation. The carbon equivalent value of 35CrMo steel is 0.72%. It is known that the weldability of this steel is poor, and the hardening tendency tends to be large during welding, especially in the quenched and tempered condition. The hot crack and cold crack tend to be large due to the heat affected zone. The welding process and measures are required to be high. Therefore, on the basis of selecting suitable welding materials and reasonable welding methods, strict technical measures must be taken to achieve the purpose of product welding.
Table 1 Chemical Composition (Mass Fraction) (%)
| C | Si | Mn | S | P | Cr | Ni | Cu | Mo |
| 0.32～0.40 | 0.17～0.37 | 0.40～0.70 | ≤0.035 | ≤0.035 | 0.8～1.10 | ≤0.030 | ≤0.03 | 0 0.15～0.25 |
Table 2 Mechanical Properties At Room Temperature
| Tensile strength / MPa | Yield strength / MPa | Elongation (%) | Area shrinkage (%) |
| ≥ 985 (100) | ≥ 835 (85) | ≥ 12 | 12 ≥ 45 |
In this article, the welding procedure of ultra-high-pressure cementing cement head is introduced, and the welding process of 5 pieces of φ52mm×17.25mm with a specification of 1 469mm long and φ326mm×18.25mm is introduced.