Chorula k. Opola 4 km from motorway A4 Mon-Fri 06:00-20:00
+48 602 716 551

Stainless Steel Welding

Stainless welding (304L/316L) for Feldbinder trailers: TIG, nitric passivation, Ra ≤ 0.8 µm, ISO 9606-1, cleanliness certificate. Chorula, Poland.

Renovation and stainless steel welding on a Feldbinder silo trailer

In brief

We weld stainless steel Feldbinder trailers (304L, 316L) using ISO 9606-1 certified welders, TIG process, with 308L/316L filler wire supplied with material test certificates. Every weld is followed by grinding, nitric acid passivation and — for food-grade trailers — a cleanliness certificate. Base: Chorula near Opole. Our scope includes accident repair and work as part of a TDT inspection.

Stainless Steel Welding for Feldbinder — A Specialist Service

Feldbinder stainless steel trailers (304L, 316L) are precision structures that demand specialist welding procedures. PHS Magnum employs ISO 9606-1 certified welders and uses fully certified tooling and filler materials. Tank shell welding is carried out in our workshop, where we can guarantee cleanliness, back-purging gas, and controlled conditions — a prerequisite for consistent weld quality and a successful TDT inspection after repair.

Materials and Procedures

Steel 304L (1.4307)

  • Most common grade for EUT trailers
  • Composition: 18% Cr, 10% Ni, low carbon content (L = Low Carbon, <0.030%)
  • Corrosion-resistant in mild environments (food-grade, most chemicals)
  • Filler wire: ER308L (standard) or 308LSi (with silicon for improved fluidity)

Steel 316L (1.4404)

  • For applications with higher corrosion-resistance requirements
  • Addition of 2–3% Mo (molybdenum) — resistance to pitting corrosion
  • Used in environments with chlorides and organic acids
  • Filler wire: ER316L or 316LSi

304L vs 316L — Material and Wire Selection

Property304L (1.4307)316L (1.4404)
Key alloying element18% Cr, 10% Ni+ 2–3% Mo (molybdenum)
Chloride resistancemoderateenhanced (pitting resistance)
Typical applicationfood-grade, mild chemicalsaggressive chemicals, organic acids
Filler wireER308L / 308LSiER316L / 316LSi
Passivation after weldingrequiredrequired

Wire selection is always matched to the tank shell material — the wire must have a chemical composition equal to or richer in alloying elements than the base material, never leaner. Further detail on cleaning and passive layer restoration is covered in our post on stainless steel — cleaning and passivation.

Filler Wire

Every wire delivery comes with a 3.1 material test certificate (EN 10204), confirming chemical composition and mechanical properties. Wire is stored in dry conditions — moisture absorption can cause weld porosity.

Shielding Gases

  • Pure argon (4.6 or 5.0) — standard for TIG on stainless steel
  • Argon + 2% H2 — for certain TIG applications (improved penetration)
  • Argon + 1–3% O2 — for MIG/MAG (improved arc stability)

WPS (Welding Procedure Specification)

Every welding repair on a TDT-regulated vessel is carried out in accordance with an approved WPS for that trailer. The WPS specifies:

  • Materials (base metal + filler)
  • Welding process (TIG 141 / MIG-MAG 135)
  • Parameters (current, voltage, travel speed)
  • Shielding gas type and flow rate
  • Welding position (PA, PB, PC…)
  • Preheat temperature (generally not required for 304L/316L)
  • Welding sequence (for long seams)

Weld Quality Control

After every weld — visual inspection (VT). For pressure vessels, additional NDT:

  • PT (Penetrant Testing) — dye penetrant inspection for stainless steel (paramagnetic)
  • RT (Radiography) — X-ray of welds for the highest-responsibility joints (e.g. external pressure-shell seams)
  • VT after finishing — to detect any micro-crack leaks

Post-Weld Passivation

Welding temperatures (1,200–1,400 °C in the weld pool) destroy the passive layer of stainless steel in the weld and heat-affected zone (HAZ). Without passivation, this area remains vulnerable to corrosion.

PHS Magnum Passivation Procedure

  1. Weld grinding to Ra ≤ 0.8 µm (Ra ≤ 0.4 µm for the most demanding applications)
  2. Cleaning — removal of grease, oil, and contaminants (isopropyl alcohol)
  3. Chemical passivation — application of nitric acid (HNO3, 20–50% aqueous solution) to weld zones and HAZ. Reaction time: 30–60 minutes depending on concentration
  4. Rinsing with demineralised water
  5. Drying with dry compressed air
  6. Passive layer test (optional) — corrosion potential measurement, potassium ferricyanide test (colorimetric)
  7. Documentation — passivation protocol filed in the trailer’s service record

Cleanliness Certificate

After welding repairs on a food-grade trailer, we issue a cleanliness certificate containing:

  • Trailer identification (model, VIN, registration number)
  • Scope of welding repairs
  • Filler materials used (wire, gas)
  • WPS procedures applied
  • NDT results (PT, RT if carried out)
  • Passivation details (date, concentration, duration)
  • Surface roughness Ra measurement
  • Leak test result
  • Welder’s signature (with ISO 9606-1 certificate number)
  • PHS Magnum service manager’s signature

This document is required by food-product recipients — a food-grade trailer should not return to service without it.

Typical Feldbinder Welding Repair Scopes

Repair typeTurnaroundScope
Minor surface micro-cracks (HAZ)1–2 daysGrinding + welding + passivation
Longitudinal seam repair2–3 daysWelding + RT + passivation
Tank shell plate section replacement4–7 daysCut-out + new section + full perimeter weld + RT + passivation
Accident repair (major damage)7–14 daysFull cycle: straightening + welding + NDT + passivation + repaint + TDT inspection

Contact

Need stainless steel welding, passivation, or accident repair for a Feldbinder trailer? Send us a description of the damage — photographs are most helpful — and we will prepare a repair plan. Ask for a quote.

  • Silo trailer service / TDT: +48 602 716 551
  • Email: biuro@magnumchorula.pl
  • Base: Chorula near Opole, 4 km from the A4 motorway junction

Frequently Asked Questions

Yes. Welding a stainless steel pressure vessel (304L, 316L) requires a welder certified to ISO 9606-1 (or PN-EN ISO 9606-1) for austenitic steel materials. For vessels subject to TDT inspection, the welding procedure must also comply with an approved WPS (Welding Procedure Specification). PHS Magnum holds ISO 9606-1 certified welders.

Passivation is a chemical process that forms a protective passive layer of chromium oxide (Cr2O3) on the stainless steel surface. We use nitric acid (HNO3) at 20–50% concentration, with a reaction time of 30–60 minutes depending on concentration. After passivation, the surface is corrosion-resistant and suitable for contact with foodstuffs (food-grade). Passivation is mandatory after any welding on a food-grade trailer.

Primary methods: TIG (Tungsten Inert Gas, process 141) — the standard choice for thin-walled Feldbinder vessels, using argon as the shielding gas. MIG/MAG (135) — for thicker sections (>5 mm) or series production work. MMA (111) — occasionally for repairs in restricted-access areas. Method selection depends on wall thickness, access, and requirements.

A cleanliness certificate is a document issued after welding repairs on a food-grade trailer. It confirms: the filler materials used (308L or 316L wire with material test certificate), the procedures applied (WPS), passivation carried out, surface roughness measurement (Ra ≤ 0.8 µm, standard requirement), and leak test results. We issue this certificate after every welding repair on a food-grade trailer — it is required by food-product recipients.

Standard: ER308L wire (per AWS A5.9) for 304L steel. For 316L — ER316L wire. Finer diameters (Ø 1.6–2.0 mm) for TIG; heavier diameters (Ø 2.4–3.2 mm) for MIG/MAG. All wire supplied with a 3.1 material test certificate (EN 10204) confirming chemical composition.

Standard: nitric acid passivation is sufficient for most food-grade and chemical applications. Passivation restores the passive layer destroyed by welding temperatures. Electropolishing is an option for trailers with the highest hygiene requirements (e.g. dairy products, pharmaceutical) — it achieves Ra < 0.4 µm. PHS Magnum carries out passivation as standard; electropolishing is available on request.

Yes — accident repair is one of PHS Magnum's core service areas. The procedure: 1) NDT inspection of damage extent; 2) repair plan and cost estimate; 3) straightening / replacement of structural beams; 4) stainless steel welding; 5) passivation; 6) exterior respray; 7) cleanliness certificate; 8) extraordinary TDT inspection. We liaise directly with insurers. Turnaround: 7–14 working days depending on the scope.

Blue or straw-coloured tinting in the weld and heat-affected zone is a sign of overheating and chromium oxidation on the surface. In these areas the passive layer is destroyed and the steel becomes susceptible to corrosion. We control heat input carefully, apply back-purging gas on the root side, and after welding we grind and passivate the area — this removes discolouration and restores full corrosion resistance.

Pressure vessel welding under TDT regulations, passivation, and NDT inspection are carried out in our facility in Chorula, where we have controlled conditions, dedicated bays, and full WPS documentation. Minor welding on external stainless fittings (handles, brackets, platforms) can sometimes be done on-site, but any intervention on the tank shell requires workshop conditions and the TDT procedure. If you have a breakdown on the road, we can help arrange transport or recovery.

A food-grade weld must be smooth and free from porosity, undercutting, and sharp transitions where product residue or bacteria could accumulate. This requires grinding to low surface roughness (Ra ≤ 0.8 µm), passivation to restore the passive layer, and documentation — a cleanliness certificate with the wire test certificate attached. Standard structural welding does not require these hygiene controls, which is why the procedure and labour time for a food-grade trailer are significantly longer.

Contact & Hours

ul. Kościelna 9, 47-316 Chorula

Mon-Fri 06:00-20:00

Sat 07:00–15:00

+48 602 716 551 Contact us
DEKRA ISO 9001:2015 Quality Management Certificate — PHS Magnum

ISO 9001:2015

4 km from motorway A4

180 km from German border

Call Email
Pogotowie Techniczne TIR & SILO +48 602 716 551