Three-layer sleeve wrapped on a weld joint already in the trench

The one band of steel the coating plant never touches

A coated line leaves the mill under factory control. Every metre of it, except the ends. Those ends are cut back so they can be welded, and the weld is made in the field. It is then radiographed, and only after that is it coated. That coating goes on in a trench, in wind or heat, at the end of a shift. The cutback is the one place on a buried line where soil, water and cathodic-protection current reach bare steel.

GTWS is the part that closes that band. It is a sleeve of cross-linked polyethylene with a hot-melt adhesive on the inside face. You do not thread it over a pipe end. You wrap it around a joint that is already welded and, on most jobs, already lowered.

The adhesive has to bond to two unlike surfaces in the same wrap. It bonds to the bare steel across the cutback, and to the pipe's own polyethylene coating on both sides of it. That is what makes the finished joint continuous rather than patched. The recovered sleeve then resists liquid pressure, bacteria, mildew, cathodic-protection current and chemical attack from liquids and solvents, and it stops the coat separation that ultraviolet light causes on an exposed run.

If the pipe end is still free, you have no reason to accept a seam at all. Settle the part type before you settle the size: wraparound or tubular.

Order it against outer diameter, and check the overlap yourself

GTWS is selected on the pipeline outer diameter, not on a nominal bore. Measure the coated OD at the cutback before you raise the requisition. Fifteen codes cover 159 mm to 1016 mm and all of them are 500 mm wide, so the sleeve covers a 500 mm band across the joint whatever the diameter.

What changes with diameter is the flat length. It runs 620 mm at 159 mm OD and 3430 mm at 1016 mm OD. Take the smallest size: the circumference of a 159 mm pipe is close to 500 mm, and the flat sleeve is 620 mm, so roughly 120 mm of it is overlap. The manufacturer does not print an overlap figure anywhere. That number is arithmetic on its own chart, and you should do the same sum for your size before the crew does it with a tape in the trench.

The closure patch grows too, from 100 mm long on the smallest code to 200 mm on the largest, at a constant 500 mm width. Every intermediate code, with its sleeve length and its patch length, is on the pipeline sleeve size chart.

Where this is the wrong part

Six situations where GTWS is the wrong thing to raise. Read these before you take the numbers above as a specification.

• It protects the field weld joint. It is not a mainline coating, and wrapping 500 mm bands along a run of failed coating is not a rehabilitation.
• It is sized to outer diameter. Below 159 mm and above 1016 mm OD there is no published GTWS code, so a 114 mm flowline is outside the range.
• It carries no pressure rating and no wall-loss rating. It is a coating, not a structural repair clamp, and it restores no metal.
• It is not a cable product. For a damaged LV or MV jacket use the wraparound cable repair sleeve.
• It does not seal a pre-insulated casing where a service pipe leaves it. That is a pre-insulated pipe sealing cap.
• It will not rescue a joint prepared badly. Peel is quoted on blast-cleaned steel and on sound PE, and neither figure survives grease, mill scale or a cold substrate.