Transitions are always possible – what to check when changing between systems

Rule of thumb

Between two systems – copper, stainless, steel, multilayer pipe, existing stock – there is always a transition; if in doubt, via a threaded joint or a flange. What has to be checked: material sequence, seal, profile – and whether the existing pipe is an approved pipe.

Where does the rule come from?

From repair and refurbishment. No contractor builds a plant twice from one system; somewhere new meets old, copper meets steel, multilayer pipe meets stainless. The worry that two systems cannot be joined is unfounded – every press system carries transition pieces with female and male thread, every steel-pipe system carries flange adapters, and thread and flange are the common language of all piping worlds.

What is technically correct?

Transitions exist on three levels. Within one profile family directly with the system transition piece (say stainless press to carbon-steel press of the same manufacturer). Between profile families and methods via thread to ISO 7 / ISO 228 (press system with threaded adapter to malleable-iron fitting, stainless threaded fitting or push-fit adapter). At large dimensions and in industry via the flange (Megapress flange adapter, Victaulic flange adapter, weld-neck flange on the existing pipe). What has to be checked: the flow rule in drinking water (first base, then noble – a gunmetal or silicon-bronze transition separates at the critical point), the new system's seal against the medium, the new system's profile against the available tool, and whether the existing pipe is, in material, outside diameter and wall thickness, a pipe the manufacturer releases for its system (pipe dimension tables).

Where does the rule end?

• It says "possible", not "arbitrary": the flow rule may force the sequence, the medium the seal, the approval the method (drinking water never via steel-pipe press systems).
• Every transition is one more joint – with a zeta value, assembly time and test effort. Threaded joints must be checked by hand, because the central leak test does not find them reliably.
• An existing pipe the manufacturer does not release (wrong material, inadmissible wall thickness, damaged surface) gets no press transition – then flange or thread at the existing end.
• In gas the transitions of the gas systems (HNBR) and the rules of the DVGW-TRGI apply; no improvised transitions there.

What does the standard say?

Threads to ISO 7-1 (Rp/R, sealing on the thread) and ISO 228-1 (G, not sealing on the thread), flanges to EN 1092-1, flow rule to DIN 1988-200, material pairings to EN 12502. Which transition pieces a system carries and onto which pipes it may be pressed is the manufacturer's statement (instructions for use, pipe overview).

DIN/EN versus ASME/ASTM

In the ASME world the transition runs via NPT threads (ASME B1.20.1) and Class flanges (ASME B16.5); NPT and Whitworth threads screw together two turns and then do not seal – a transition between the two worlds needs an adapter with both threads or a flange with the matching bolt pattern.

Worked example

Refurbishment: an existing galvanised steel main DN 25 is to be connected to a new stainless-steel press line 28 mm. At the existing end a threaded transition (Rp 1 to press 28) in gunmetal – it also separates according to the flow rule, because the galvanised steel lies upstream of the stainless. The existing pipe is not pressed but connected at its existing thread. One transition, one check by hand, done.

Zickwolff reference

Experience from repair and refurbishment (Martin, 24.09.2026): "The transition between systems can always be made – if in doubt via a threaded joint." Zickwolff stocks the transition pieces of the press systems alongside malleable-iron fittings, stainless threaded fittings, flanges and gaskets – the parts for the transition come from one warehouse.

Checked today

Traffic light: applies (class A). A transition can always be made technically; the conditions (flow rule, seal, profile, pipe release) are checking steps, not exceptions. The rule does not replace the system's instructions for use.

Further reading

• Mixed installation and corrosion: flow rule, material pairings, drinking water – flow rule and material pairings
• Press profiles and tools: V, M, SA, SC-Contur, press jaws, press rings, press machines – which profile belongs to which tool
• Leak testing and SC-Contur: dry testing, unpressed = leaking, load test – why threads are checked by hand
• Malleable iron fittings to EN 10242: threads R/Rp, GF type numbers – malleable-iron fittings for threaded transitions
• Stainless steel threaded fittings: threads, standards and why lengths vary – stainless threaded fittings
• Flange standards explained: EN 1092-1, DN, PN, types & sealing faces – flanges for the transition in industry
• Few systems, one profile – when the rule applies and when it does not – the sister rule on the number of systems