Disadvantages of Outer Thick Tubing

1. Low processing efficiency, serious waste of factory capacity
Although the thickened tubing increases the connection strength of the tubing, the thickening of the tubing must be achieved through the thick and secondary heat treatment process. The efficiency is extremely low, and once the thread processing is unqualified. According to the statistics of Tiangang and Baosteel, the time required for pier roughing + heat treatment and the cost increase must be re-performed. Therefore, the cost of externally thickened tubing has remained high.

2. After the joint is prone to slip failure under tensile load
Due to the interference between the internal and external threads, the load bearing surface and the guiding surface of the thread are subject to the forces FL and FS, respectively. When the joint is subjected to an axial tensile load, the force FS on the guide surface decreases and the force FL on the load surface increases; at the same time, FS and FL also decrease slightly due to Poisson effect. When the tensile load continues to increase, the guide surfaces of the internal and external threads gradually separate, FS becomes 0, and only the bearing surface is stressed. When the tensile load is increased to a certain level, the friction between the bearing surfaces of the internal and external threads can be gradually overcome. At this time, relative sliding between the bearing surfaces will occur, and slippage failure will occur.

3. Can't meet the requirements of gas seal under higher pressure
Due to the gap of 0.076mm, the outer thick oil pipe thread has problems such as incomplete structure and insufficient air tightness, and can only be used in some common well conditions. For increasingly complex geological environments and well conditions: such as deep wells and ultra-deep wells , High-pressure gas wells, heavy oil thermal recovery wells, directional wells, horizontal wells, and heavily corroded wells appear to be inadequate. Occasionally, accidents such as leaks occur.

4. The performance of the upper shackle is not good and the anti-sticking ability is poor.
Because the uneven distribution of the stress after the buckle is easy to cause thread sticking, the internal and external threads have the largest contact stress at the first effective thread, and the local maximum stress can reach 4 times or more of the intermediate tooth surface stress, and the contact stress causes thread sticking. The root cause of the thread, the tooth surface at this position is the easiest to buckle during the thread loading and unloading process.

5. Limited thread repair
Leu standard length is 41/4in, 107.95mm, minus L4 length 2.313in, the remaining repairable length is only 1.937in, 49.19mm, and the normal length of each loss during thread repair is 20mm, that is, The root can only be used 2-3 times, and the thickened part is too short, which is prone to slippage of the elevator part, resulting in an accident of falling of the pipe string. However, most of the pipe bodies are still intact after 2-3 uses, thus causing great waste and economic loss to the oilfield.
Especially the current oil during the period of low prices, it is of great practical economic significance for oilfields to make the most of the potential of oil pipes, reduce costs and increase efficiency, and save oil production costs.

6. Difficulty processing accessories such as short sections
Due to limitations in the upsetting process, quantity, and length of the outer thick tubing, it is not possible to achieve large-scale production in the factory, or even the production is costly. Entrusted to small factories for processing. Due to the absolute number of anti-sulfur oil pipes of the branch, small manufacturers could not produce metal materials resistant to hydrogen sulfide. Even if the production could not guarantee the anti-sulfur performance due to technical and equipment reasons, there was a huge potential safety hazard. Therefore, short sections of anti-sulfur tubing are difficult to order, high in price, high in cost, and long in cycle.

7. The tubing order cycle is long, the price remains high
Due to the effect of the thickening process of the outer thickened tubing, the tubing production cycle is long and the price is high, which has a greater impact on the anti-sulfur tubing. According to incomplete statistics of the factory, the thickening process results in an increase of about 800-1000 yuan / ton.

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