API16 Key technical control points for high-pressure straight pipes

High-pressure manifolds are widely used in drilling, cementing and fracturing, and the working pressure of drilling manifolds is usually less than 50 MPa; The working pressure of cementing manifolds is usually less than 70 MPa; The working pressure range of fracturing manifolds is relatively large, and the current maximum working pressure is close to 140 MPa. Used for sanding fracturing manifold high-pressure straight pipe, in use, there is a long construction cycle, high construction pressure, frequent alternating changes in construction process pressure, high construction flow, fast erosion speed of fluid particles and other reasons causing stress aggregation of high-pressure straight pipe, fatigue of high-pressure straight pipe, erosion of fluid particles causing thinning of pipe walls is the main reason for the failure of high-pressure straight pipe.

From raw materials to finished products, high-pressure straight pipes need to go through the following processes: raw materials are inspected in a normalizing state→ unloading→ heating pier rough forging→ quenching and tempering treatment→ flaw detection → finishing→ flaw detection → assembly → testing (strength and sealing) → spraying. Among them, the quality control of raw material composition, pier rough forging, heat treatment, and seals is particularly important for the finished product quality of straight pipes.

First, raw materials

1, high-pressure straight pipe steel on the chemical composition and quality control requirements are strict, raw material requirements to ensure the necessary strength and sufficient toughness, if necessary, should also meet the special performance requirements of low temperature. The existing high-pressure straight pipes used in the market mainly include 4130, 4140, 30CrMo, etc., and the chemical composition of good steel should strictly control the harmful element content (S, P content), and add the necessary alloying elements; The microstructure should also have a finer grain size.

2. Specifications of raw materials

The seamless steel pipe used in the 2-inch straight pipe on the market has a variety of specifications such as ∅63.5*10, ∅68*10, ∅68*12; The seamless steel pipe used in the 3-inch straight pipe has a variety of specifications such as ∅89*10, ∅89*12, ∅89*14, ∅89*15, ∅95*15; Xi'an Qinsen Technology Co., Ltd. straight pipe using daye special steel raw material production, two inches of straight pipe recommended to use ∅ 68 * 12 straight pipe, three inches recommended use of ∅ 95 * 15 straight pipe, that is, take into account the safety, but also improve the overall diameter;

Second, the pier is roughly forged

The straight pipe after the rough forging of the upsetting should maintain a smooth appearance shape, and the normal end forging should be achieved by three fires (Figure 5), and the uniformity and mechanical properties of the material properties are guaranteed. In order to save costs, low-cost products will choose two-fire forging, which increases the risk of forging defects, accompanied by local pits, mold indentations, rust and other quality problems, and even some manufacturers directly use the form of surfacing welding to achieve (Figure 6), the simplification of the process, for the future use of products buried a variety of quality hidden dangers.

Third, heat treatment

For the overall performance of high-pressure straight pipes, the quality control of heat treatment is of equal importance to the control of material chemical composition; The existing straight pipe materials are 4130, 4140, 30CrMo, etc., and the main heat treatment process is quenching and tempering treatment. In the process of quenching and tempering of the straight pipe, the uniformity of the high temperature cooling rate is directly related to the overall performance of the straight pipe, if the quenching process is horizontally into the water, because the straight pipe is long, it will lead to the presence of steam in the middle part, affecting the uniformity of the temperature reduction speed, so the vertical water is easier to ensure the quality of the overall heat treatment of the straight pipe than the horizontal water.

Fourth, the quality control of the seal

The material of the straight pipe end face seal is hydrogenated nitrile rubber (HNBR) and nitrile rubber (NBR), HNBR high temperature resistance is 130 ~ 180 °C, cold resistance is -55 ~ -38 °C, excellent mechanical properties, acid resistance, oil resistance, solvent resistance; NBR has a high temperature resistance of 120 °C, and its low temperature resistance and acid resistance are weaker than HNBR. The sealing material used in Qinsen's straight pipe products is HNBR.

The form of straight pipe end face seals has copper rings, steel rings and no metal rings (Figure 9), the anti-deformation ability of seals with metal rings is good, the ductility of copper rings is better than that of steel rings, the use of copper rings in the three types of sealing rings is the best, but the price is high, Qinsen company's straight pipes above 70MPa are used with copper ring seals.

Fifth, the strict quality control of the whole process

Founded in 2001, Xi'an Qinsen Technology Co., Ltd. is committed to the research, development, manufacture and sales of gas wells and oil and water wells with pressure equipment and accessories, accessories, standard parts and wellhead tools. The company has obtained ISO9001-2008 international quality management system certification, API Spec 7K certificate and API Spec 16C certificate. The design and production of all products are carried out in strict accordance with the requirements of API processes and management system standards.