The studies and experience indicate that the application of nickel-based alloy steel in high sour environments is greatly restricted due to its cost, which is 20 to 25 times the cost of corrosion-resistant steel, despite the fact that it has high resistance to corrosion in high sour environments. It has very high cost performance and involves the outstanding performances of both carbon steel and corrosion-resistant alloy steel.
Its corrosion resistance is the same as that of corrosion-resistant alloy steel. Base pipe and liner, which is a thin-wall corrosion-resistant alloy steel pipe, are coaxially assembled at first, and then a hydraulic power pipe is assembled in the liner. Carbon steel pipe can be manufactured using several different techniques, each of which produces a pipe with certain characteristics.
Seamless pipe is formed by piercing a solid, near-molten, steel rod, called a billet, with a mandrel to produce a pipe that has no seams or joints. Butt-welded pipe is formed by feeding a hot steel plate through shapers that will roll it into a hollow circular shape. Spiral-welded pipe is formed by twisting strips of metal into a spiral shape, similar to a barber’s pole, then welding where the edges join one another to form a seam.
This type of pipe is restricted to piping systems using low pressures due to its thin walls. Figure 2.3 shows spiral-welded pipe as it appears before welding. Figure 2.4. Manufactured carbon steel pipe.
Butt-welded pipe, for example, is formed from rolled plate that has a more uniform wall thickness and can be inspected for defects prior to forming and welding. Pressure Piping Code B31 was written to govern the manufacture of pipe. However, for the many low-pressure uses of pipe, the continuous welded method is the most economical.
The pipe must withstand the pressure, temperature, and corrosion conditions of the application. Note: Cost based on FOB mill price January 2015 for electric resistance-welded pipe. Some corresponding international standards for carbon steels and stainless steels are shown in Table 3.5.
SMLS pipe, where available, is used in oil and gas production facilities both onshore and offshore (other than transmission lines) less than 26″ (660.4 mm) OD. The pipe is not fully normalized after welding, thus producing a heat-affected zone on each side of the weld that results in nonuniformity of hardness and grain structure, thus making the pipe more susceptible to corrosion. SAW and DSAW pipes are produced from plate (skelp’s), which are either formed into a U” and then an ” and then welded along the straight seam (SS) or twisted into a helix and then welded along the spiral seam (SW).
Furnace butt-welded pipe is normally used for domestic (United States) and firewater service only. At the end of the coil, a new coil is butt-welded to the trailing edge of the pipe, forming a cross seam. Spiral-welded pipe is primarily used for water distribution service.
For structural steel members where strength requirements predominate, it is common to add a corrosion allowance to thickness.