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Tube Installation, Welding & Maintenance

Information Center

Minox Hoses Installation Guide
Passivation: A Critical Process for Stainless Steel Applications
Clean-In-Place (CIP) Process Instruction
Surface Finishing of Food Grade Stainless Steel Tubes and Fittings
Minox Stainless Steel Tubes, Valves and Fittings for Food/Pharma
Welding of Sanitary Tubes, Valves and Fittings

A. Unpacking/Delivery

MINOX delivered the materials in the agreed quality.

Check the delivery:

  1. Mill certificates numbers shall match with heat numbers engrave on pipes as in Figure
  2. All MINOX pipes shall have an internal surface roughness of 0.8µm Ra maximum.
  3. Longitudinal welding in pipes shall not show any discoloration on the inside.

Figure 1: Example of MINOX pipe heat number.

Pipes must be resealed to avoid impurities and/or small insects come in to the pipe. All pipes must be stored in a dry and dust free room.

B. General Installation

Care shall be taken that any closed process line can be fully drained.

  1. Pipes shall be mounted so as to be fully drainable with slope ≥ 3° towards draining point as in Figure 2.
  2. Horizontal pipelines shall use long eccentric reducers to change pipe diameter as in Figure 3 to avoid undrainable pockets.

Figure 2: Fully drainable pipeline with slope at 3°.

  1. For vertical pipes use of concentric reducer is allowed.
  2. If the location prevents drainability problems, valves must be built in at all low points of the installation.
  3. Supports or hangers for piping shall be installed in such that no water or soils can remain on the surface or within the support.
  4. Clearance between piping and construction (floors, walls and ceiling) must be adequate for cleaning and inspection.

(a) product area, (b) concentric reducer, (c) eccentric reducer, long version, (d) eccentric reducer, short version, (e) potential shadow zone. Source: EHEDG Guideline 10.

Figure 3: For horizontal pipe, eccentric reducers are preferred.

All document details are in accordance with EHEDG Guideline 8 and 10.

C. Welding

Welding of product pipes must only be carried out by certified welders.

  • Pre-welding
    1. Tube end shall be properly cleaned from oil and dirt prior to welding.
    2. In the case of cutting, it shall be done by using mechanical tools such as tube saw and tube facing machine. This ensures a flat square tube ends without burrs or chamfers as in Figure 4.
    3. Only TIG welding and orbital welding are acceptable for hygienic weld.

Figure 4: Square end of tubing (free of burr).

  • Welding
    1. During welding, inert gas such as nitrogen or argon shall be used on the front and on the backside of the weld zone.
    2. Straight forward butt weld shall be used for hygienic tubing and fittings.
    3. The butt weld joints shall be properly cleaned within 25mm of the joint area on the inside and outside surfaces prior to welding.
    4. Pipe ends to be welded must have identical inside and outside diameters. In case of any difference, the smallest pipe must be expanded to the big inside diameter.
    5. The gap between pipe faces or between pipe and fittings shall within 0.25mm and misalignment tolerance of less than 20% of wall thickness as shown in Figure 5.

Figure 5: Limitation of gap and misalignment tolerance of weld.

  • Post Weld Inspection and Treatment
    1. Weld piping systems shall be inspected visually or by endoscopy.
    2. The weld joint surfaces shall be penetrated completely to the internal surface (Figure 6), no under or over weld penetration (Figure 7), no surface defects such as inclusion, cracks or porosities and lack of fusion.
    3. Pipe ends to be welded must have identical inside and outside diameters. In case of any difference, the smallest pipe must be expanded to the big inside diameter.
    4. The gap between pipe faces or between pipe and fittings shall within 0.25mm and misalignment tolerance of less than 20% of wall thickness as shown in Figure 5.

Figure 6: Incomplete penetration of weld is not acceptable. Source: EHEDG Guideline 35.

Figure 7: (a) Convexity on the internal diameter should not be greater than 10% of the wall thickness of the thinner tube. (b) Concavity on the outer diameter of the pipe should be less than 15% of the wall thickness of the thinner tube. (c) Concavity on the internal diameter of the pipe should be less than 10% of the wall thickness of the thinner tube. Source: EHEDG Guideline 35.

  • The weld can be pickled on the outside with pickling paste to remove the “heat colours”.
  • For product contact weld surface, degreasing treatment can be applied to remove the grease and oily residues by using an alkaline detergent solution.
  • If there is additional requirement, passivation can be carried out by using nitric acid to increase the corrosion resistance of the weld areas.

All the inspection and treatment used must be approved by the customer and his safety representative before it can be implemented.
All document details are in accordance with EHEDG Guideline 9 and 35.

D. Maintenance

Proper pipeline maintenance shall be done through regular inspections and repairs to maintain the integrity of a pipeline.
A maintenance checklist shall be developed to:

  1. Check any obvious leaks or corrosion which would be characterized by puddles of product, chemical or ingredients on the floor, odd smells if the leaking product is a gas and discoloration on pipes.
  2. Clean the pipes frequently depending on the type of processes.
  3. Replace, upgrade and rehabilitate the pipes depending on the age of your piping system.