SMLS pipe is used in high-pressure, most critical locations and under most severe operating conditions. ERW pipe is made from coils that are cupped longitudinally by forming rolls and a thin-pass section of rolls that brings the ends of the coil together to form a cylinder. The weld is then heat-treated to remove welding stresses and the pipe is cooled, sized to the proper OD, and straightened.
Table 3.4. Comparison of steel pipe versus other alloys. Table 3.5. Comparison: US and international specifications for steel pipe. SMLS pipe is produced by heating a round billet of steel and then piercing it with a bullet-shaped piercer, over which the steel is stretched.
220.127.116.11.4 Furnace-weld, butt-welded, or continuous weld (CW) pipe. The pipe is then pulled through a ring die or bell and the pipe is welded by pressing the edges together at a high temperature. Butt-welded pipe is supplied according to ASTM Specifications A53 and A120 and API Specification 5L for line pipe.
Furnace-butt weld pipe is not recommended for use where internal corrosion is anticipated. Spiral-welded pipe is available in sizes from 24 in. (60 cm) to 144 in. (365 cm). 17.20 External and Internal Protection of Steel Pipe.
As an alternative, coal tar has been used, particularly for underwater pipelines, but has lost favour in view of health and safety issues. Alternatives such as FBE and 3LPE for buried and exposed pipes are now preferred. FBE coatings generally have better resistance to cathodic disbonding than brush or spray-applied coatings when used on cathodically protected pipelines.
Completion at joints is by heat shrink sleeves (favoured for larger pipe diameters) or by tape wrap. Pinholes or breakages are disclosed by an electrical discharge to the steel of the pipe and this can be arranged to cause a buzzer to sound. A hot applied bitumen with or without an inert filler is sprayed or brushed onto the pipe, after first priming it with a compatible priming coat; the usual practice was to apply a minimum thickness of 1.5 mm for diameters up to 300 and 6 mm for diameters exceeding 1000 mm.
BS EN 1295-1 covers structural design of buried pipelines for the water industry. EW pipes now tend to be known as HFI (high frequency induction) pipes. Pipe wall thickness, t (mm) for internal pressure is determined by hoop stress, as follows:
Design factors for hoop stress typically range from 0.4 to 0.8; the joint factor is 1.0 for SAW pipes and certain codes require the negative tolerance to be deducted from wall thickness. For many water supply pipelines wall thickness is determined by handling and installation and the need to control deflection. However, fittings can be made to any dimensions required, bends being made by cutting and welding together sections of pipe.
A major problem is liner collapse, which can occur when the pipe is depressurized, due to the presence of pressurized gas which has permeated the liner, to fillany void space at the interface between the liner and the pipe inner wall.