Depending on the process situation, basically it’s safe to say that the default choice for pipeline system in food and beverage process industries is austenitic stainless steel, 304/304L or 316L. Comparatively, there is no difference in corrosion resistance between 304 and 304L, but low carbon content (0.03% max) plays an important role to the “after-weld condition” on the steel.
To connect various processing equipment to sanitary grade stainless steel valves, tubes and fittings, the most common method is by welding. Hence, by performing an excellent welding job on adequate material will bring higher level of hygiene qualities required to the process line. Heating stainless steel to temperature ranging 425°C to 860°C for several minutes inevitably lead to the formation of chromium carbide, which can be seen as yellowish heat tinting zone, that contributing to significant loss of corrosion resistance. By choosing 304L or 316L type of stainless steel tube and fittings, the risk of this intergranular corrosion will be lowered down to almost none.
Selecting an unsuitable material will bring defect on the weldment. There are some other reasons that act as the source of microbiological problem that occurred on the welding zone, for example misalignment, incomplete penetration by poor welding technique, lack of gas shielding, to name a few.
Note: Most of the time, tubes and fittings suppliers would be finger pointed for corrosion that took place at welding zone of food process pipeline. The main concern for user is if they have been cheated on the material supplied to them. This should not happen if users select a well-established brand name with proven quality record and support. Good supplier will provide material and inspection certificate on each and every piece of product based on the trace number printed on it. Minox provides all information required by user and help to analyze weldment defect together with third party laboratory if called upon.