Wraparound or tubular: one question decides it

The question is about access, not about the part

A tube comes out of the box and there is nowhere to thread it. The feeder is live at both ends. The pipe is welded into the line. The pole is in the ground. Nothing is wrong with the material, the code or the diameter, and the part is still scrap.

So settle one thing first. Can you reach a free end, and can you afford the outage it would take to make one?

Two answers, two part types. A free end you can reach means a tube. It threads on from that end, recovers all the way round, and carries no seam anywhere on it. No free end, or an outage nobody will authorise, means a wraparound. It leaves the factory slit down its whole length. You fold it round what is already standing and close the seam yourself.

The second half of the question does most of the work. A free end nearly always exists somewhere. Reaching it means dropping the feeder, cutting the run, or unbolting the support. On a distribution circuit that is a notified outage with a window and a crew. The manufacturer states that a wraparound repair needs no system shutdown, and that one sentence is the commercial case for the entire family.

The wrap buys access and charges a seam

That is the whole trade, and the seam is where the charts stop agreeing with each other.

Two closure systems carry the load, and they publish very different amounts of evidence. On the GWS cable sleeve the closure is a zip-up stainless steel channel running the length of the seam. It is mechanical. It holds the lap shut while the adhesive underneath is still soft. No property of that channel appears anywhere on the sheet.

On the GTWS pipeline sleeve the closure is a separate patch. It is shrunk over the lap after the wrap is made. It is a second component with its own row on the chart. The patch is 100 mm long on a 159 mm pipe and 200 mm long on a 1016 mm pipe. Its technical specification is headed for the sleeve and the closure patch together, so those figures cover both. Tensile strength is 22 N/mm² and elongation 550 per cent. The method is ASTM D638. Peel to steel is 100 N/cm at 25 °C and 30 N/cm at 50 °C. The method is ASTM D2671.

Now look at what each kind of chart chooses to measure. A tubular chart gives a wall thickness. The GMW pole tube is charted at 3.3 to 3.5 mm, to a tolerance of plus or minus 10 per cent. That wall is uniform the whole way round by construction. A wraparound chart usually gives an overlap in that column instead. GMRS states a minimum overlap and no wall. GPWS states a minimum overlap and no wall. GTWS states a closure patch size and no wall. Only GWS publishes a recovered wall. It is 2.7 mm, and it holds on every code in the range.

That 2.7 mm is the wall everywhere except at the lap. Two thicknesses sit on each other there. So the polyolefin at the seam is at least 5.4 mm, with the steel channel standing proud of it. The finished sleeve is thickest and least uniform at precisely the point the closure occupies. That is why the closure map on this site is dimensioned against the substrate rather than drawn as an illustration.

Where a wraparound is the wrong part

A reachable free end changes the answer. So does anything that would put the seam where the asset gets worked.

• An asset not yet installed. The manufacturer charts both parts side by side on one pole sheet. The two headings are protection for installed poles and protection for un-installed poles. It recommends the tubular GMW sleeve on fresh poles before they go into the ground. Same job, same 700 mm length, and the wrap is reserved for what is already standing.
• A damaged length longer than the longest sleeve. GWS runs up to 1500 mm and GMRS is stocked at 100, 200, 300 and 400 mm. Cover two metres of torn jacket and you are fitting several sleeves, each with its own seam and its own pair of end seals. On a reachable end, one cut length of tube does it with none.
• Anywhere the seam would land in the worst mechanical position. A duct pull drags on one face of the run. Backfill stone bears on the underside of a direct-buried one. A tube has no seam to place, so the judgement never has to be made.
• A specification that forbids a longitudinal joint. Some coating specifications call for continuous recovery with no seam of any kind. No wraparound meets that wording, and no amount of overlap will argue it round.
• A part that is sized on a shank rather than a circumference. The U-bolt tube slides over the bolt before the clamp is made up. It is tubular, and it appears on this site only because the pipe it clamps stays in service. See U-bolt support corrosion.
• Ordering with only one dimension in hand. A tube is picked on diameter and cut to length. A wraparound needs a circumference and a stocked length together, so the requisition carries two columns instead of one. Both sit on the heat shrink sleeve size chart.

The third option, in two sentences

Cold shrink cannot be closed around an asset already in place, because it recovers off a removable core that has to be threaded on first. Every cold shrink figure, the mechanism and the voltage ceiling sit on the same publisher's tubing reference at shrink-tube.com, which holds those datasheets.