Store stainless pipes dry, separately and without film – why a pipe can start corroding in the warehouse

Rule of thumb

Dry and ventilated so that no condensation stands; separate from carbon steel so that no foreign rust gets onto the surface; without film because film holds condensation. What is neglected in the warehouse shows up later as flash rust or pitting on the finished line.

Where does the rule come from?

The rule comes from the storage instructions of the system manufacturers. Geberit writes for its system pipes: store only in dry, well-ventilated areas, not directly on the floor, on cantilever racks or dry squared timbers with at least three support points without sagging; do not cover with film because film promotes condensation; store stainless, Therm and carbon-steel pipes separately to avoid contact corrosion; open mixed bundles after transport and store by type; protect from weather and moisture, the dew point must not be undercut.

What is technically correct?

Stainless steel protects itself through its passive layer – as long as the surface is clean and supplied with oxygen. Two things disturb that in the warehouse: foreign iron (grinding dust, abrasion, contact with carbon-steel pipes or racks) which rusts on the surface and breaks through the passive layer locally, and standing moisture under film or in pipe bundles in which chlorides concentrate. Hence: separate storage places or spacers, no film, air around the pipe, pipe ends with plugs, do not drag pipes over loading edges (scratches are starting points).

Where does the rule end?

• Plastic-coated carbon-steel pipes are deliberately delivered by the manufacturer in a film sleeve – there the film protects the coating from dust; the rule “without film” applies to bare metal pipes.
• Short intermediate storage on site in the original packaging is fine – the packaging protects the pipe ends; without packaging the protection must be provided otherwise.
• For carbon-steel pipes the same rules apply for the opposite reason: they rust themselves, and their rust must not get onto the stainless steel.
• The rule does not replace an external-corrosion assessment in the plant (chlorides from insulation, screed, environment) – for that see mixed installation and corrosion.

What does the standard say?

There is no standard for the storage of pipes; manufacturer data and the general rules on corrosion protection apply (DIN EN 12502 for drinking-water installations, DIN 50930-6 for material selection). The delivery conditions of the pipe standards (EN 10312, EN 10217-7) govern surface and condition at delivery, not storage afterwards.

DIN/EN versus ASME/ASTM

In the ASME/ASTM world storage is likewise not in the material standard (ASTM A312, A269) but in fabricator guidelines (such as Nickel Institute / ASSDA practice): separate from carbon steel, no contact surfaces of unalloyed steel, dry, caps on the ends. The rule is the same worldwide, only the source has a different name.

Worked example

A maintenance team stores stainless system pipes next to black threaded pipes on the same steel rack, in film against the dust. After a damp winter the stainless pipes show brown spots at the support points and under the film – foreign rust and condensation. The pipes have to be cleaned and inspected before installation; with timber supports, without film and one rack place further away nothing would have happened.

Zickwolff reference

From daily business: we store stainless and carbon-steel pipes separately and deliver stainless pipes with plugs; for project deliveries we pack by material and mark the bundles so that they are not stacked mixed on site (solution page packaging and marking). Pipes that are to lie on site for a long time go, on request, supported on wooden battens and without film – in cardboard only what stays dry in cardboard.

Checked today

Verdict: applies (class A). The rule follows the manufacturer’s storage instructions and the corrosion mechanism; it is a warehouse truth, not an interpretation of a standard.

Further reading

• Packaging and marking: picking by construction phase, line and item – up to export packaging – Packaging and marking – project delivery and long-term storage
• Mixed installation and corrosion: flow rule, material pairings, drinking water – Mixed installation and corrosion: external corrosion by chlorides and moisture
• Materials between the worlds: material number to UNS and ASTM grade – and the limits of comparison – Materials between the worlds
• A repair clamp is a repair, not a new build – what repair clamps and repair bands may do permanently and what only until the next opportunity – A repair clamp is a repair, not a new build
• Steel pipes explained: EN 10216/10217, seamless or welded, test categories TC1/TC2 – Pipes to standard in the pipe finder