Megapress or welding? Joining thick-walled steel pipe – the decision criterion by criterion

What it is really about: not the joint, but everything around it

The weld seam is the strongest pipe joint there is – a metallurgical bond, without sealing element, in every size, wall thickness, pressure and temperature rating. That is not the point. The point is what a weld seam brings with it: it is hot work. In existing plant that means welding permit, fire watch, gas-free certification in areas with gas or dust, covering or removing combustible materials, often draining and drying the line, plus a qualified welder, a procedure qualification for the application and a seam that can afterwards only be judged by visual, pressure and, where required, non-destructive testing.

The press joint takes all of that out of play. It is cold, made in seconds and immediately loadable; the forgotten press shows up by itself at the leak test through the SC-Contur. In return it has limits: 16 bar, 105 or 140 °C, 4 inch, a sealing element that must suit the medium, and it is – like the seam – permanent. The decision is therefore not a question of strength but a question of boundary conditions: existing plant or new build, running operation or shutdown, size, medium, pressure, temperature – and who is standing on site.

The four methods compared

The table sets the press joint (Megapress) against the weld seam and adds the two detachable methods that have a say from DN 65: the grooved coupling (with us Victaulic) and the flange. Every row names where the statement comes from – manufacturer statement, code or experience from trade.

Figures on time savings are manufacturer claims and refer to making the joint under the manufacturer's conditions; they do not replace a costing for the specific site. The full comparison of all seven methods – additionally push-fit, thread and soldering – is in the joining methods comparison.

Where welding remains

There are cases in which the question is not open at all. Welding continues to be used:

• above 4 inch (DN 100): Megapress ends at 114.3 mm. Above that, welding, flange and grooved coupling are the methods – the coupling up to DN 600 and more.
• above 16 bar or above 140 °C: the press connection system is designed for PN 16; with FKM up to 140 °C. Higher pressure ratings and temperatures are a matter of design by material and wall thickness – that is, of the weld seam and the flange in PN 25 to PN 100.
• steam and pressure equipment subject to inspection: saturated steam, hot water above the system limits, piping within the scope of the Pressure Equipment Directive designed to EN 13480 – here procedure qualification, weld testing and documentation apply, which the press joint does not provide. (Megapress S can be used for low-pressure steam only by agreement with Viega.)
• wall thicknesses outside the pipe overview: very thin-walled welded pipes below the minimum and very thick-walled pipes above the maximum of the respective size cannot be pressed reliably.
• drinking water: not because of welding, but because Megapress is not approved for it; here system-pipe systems in stainless steel or copper (Sanpress, Profipress, NiroSan) or welded stainless-steel pipe come into question.
• fittings that do not exist as press connectors: special branches, reductions over several nominal sizes, bends with special radii – the elbows, tees and reducers to EN 10253 cover that and are welded in.

Decision aid: five typical cases

The following cases are the ones we meet most often on the phone. They replace neither the design nor the manufacturer approval – they pre-sort the question.

Three questions are usually enough for the preliminary decision: Is the joint within 4 inch, 16 bar and 140 °C? If not: weld or flange. Does the medium suit a sealing element? If not (steam, drinking water, unknown chemical): weld or system pipe. Is the work in existing plant, in an occupied building or without shutdown? If yes: press or groove – and only then calculate.

And the costs?

The press connector costs more than the fitting that is welded in – that is the material premium the assembly has to earn back. Whether it does depends on a few quantities: number of joints, size, hourly rate and number of fitters, set-up and finishing time per joint, costs for fire watch, permit and gas-free certification, testing and documentation – and, in operation, the downtime cost per hour. The cost comparison calculator puts these quantities side by side for press, welding, grooved and flange, with preset assembly times whose origin is visible and which can be overwritten with your own inputs. It calculates a model, not an offer – and it does not replace costing or the manufacturer approval.

Both from one source

Whatever the decision turns out to be: the components for it lie side by side with us – thick-walled steel pipe to EN 10255 and EN 10220, butt-welding fittings to EN 10253, flanges to EN 1092-1, Megapress connectors and adapters (sourced from Viega) and grooved couplings from Victaulic. The standard names dimensions. What is listed here, we carry – from stock or to order; how quickly a size is available we clarify on request.