Pipe Installation, Bending, and Alignment
Stringing and alignment
Stringing places joints along the right-of-way with bevels protected and coating intact, on skids positioned to avoid point loading and to allow the bending and welding crews to work. Alignment covers ditch line, horizontal and vertical curves, and clearance from other structures. Internal line-up clamps and external clamps bring joints to fit-up tolerance; hi-lo and gap are measured, not eyeballed.
Field bending
Cold field bending matches the pipe to terrain. Know the concepts: minimum bend radius is set by project specification and pipe grade, diameter-to-thickness ratio, and coating type; wrinkle bends are not permitted in modern pipeline construction; ovality and strain limits apply; and springback must be accounted for when setting the bend. Bends are numbered, measured, and recorded so the as-built reflects what was installed.
Lowering-in and buoyancy
Lowering-in is a controlled operation using matched sidebooms, with the pipe kept from overbending, coating protected, and the ditch free of rock or debris. Buoyancy control includes set-on or bolt-on weights, concrete coating, screw anchors, and swamp weights; casings, casing insulators, and vents are installed where specified.
Traps
Common question traps: bending a joint that contains a weld in the bend arc; assuming bends may exceed the specified radius slightly; confusing springback with overbending; and allowing coating to be damaged because padding was skipped. Another trap is treating a bend count as optional paperwork - bend records frequently surface in integrity digs decades later.
Worked example
Rule of thumb: if the crew "needs" a tighter bend than the specification allows, the correct answer is a fitting, a different alignment, or a design change - not a hotter bend. Document the bend number, location, angle, and radius on the bend record before the joint is welded in place.