Casing coupling problems continue to arise. Can new materials break the bottleneck?

Continuing developments in gas well and fracturing design concepts have driven casing collar design concepts forward. The casing couplings currently used must be inserted into the well section of three or four miles under high pressure conditions. This necessitates continued efforts to improve the stability of casing couplings.

When workers drill wells, they generally use casing threads. In order to improve performance indicators, casing couplings are generally made of high collapse resistance P110 grade. More and more couplings are broken due to hydrogen embrittlement. The main culprits of hydrogen embrittlement cracking are: susceptible components, hydrogen sources and high stress. Even in low-sulfur wells, acid treatment can introduce hydrogen. Although the high collapse resistance coupling blank is to better improve the collapse resistance of the casing string, it ultimately increases the probability of hydrogen embrittlement fracture. For P110 grade materials, the allowable yield strength range is between 110 and 140ksi.

Many coupling ruptures occur in the range of 130 to 135 ksi. When running casing and couplings, speed and accuracy are very important, and speed cannot be increased in order to reduce costs. If it is inserted too hard, or the coupling is buckled off-center, or the pipe string falls into the well, all the costs saved by increasing the operating speed will be lost like the pipe string falling into the well.