Manways for food production

Food production, processing and preparation, are very demanding areas in terms of maintaining high standards of hygiene. Stainless steel manway covers operating in this specific environment are not infrequently exposed to high temperature, high pressure and sometimes vacuum. What's more, the most important condition, which determines whether a manway is approved for use in a food installation, is its hygienic design.

The multitude of processes in which stainless steel manways are involved results in a very large number of models that are used in the food industry. This is influenced by both specific factors in the work environment and the demands of the day-to-day operation of processes and production equipment.

The wide range of available manway models provides a base from which designers of tanks, equipment and installations necessary in the processes of production, refining and storage of food and beverages draw. Selecting the right model for a given application requires establishing a number of parameters and factors so that the manway meets not only the requirement for hygienic construction, but also the design requirements (such as dimensions, resistance to temperature, pressure/vacuum, chemical effects of working media and similar).

Food safety management systems (e.g., HACCP), used in food establishments and in the food service industry, specify methods to reduce risks in the production process. Sanitary standards such as 3-A Sanitary Standards serve a similar function, ensuring that the highest standards of hygiene are maintained. All this so that we can be sure that the food we eat every day is safe for us. For this reason, materials such as stainless steel or elastomers used in the manufacture of manways must have the right properties and characteristics that are conducive to maintaining the required level of hygiene. In addition, they must meet the requirements of Regulation (EC) No. 1935/2004 of the European Parliament and the Council.

The most common grades of steel used in the food industry are AISI 304 (1.4301) and AISI 304L (1.4307). A certain number of manways are also produced in steel grades AISI 316 (1.4401) and AISI 316L (1.4404). The stainless steel used for manways is characterised by both good weldability and possibility of surface treatment. The smooth – sanded or polished surface – is often a key element, determining the use of a manway in the food industry. Among the food manways are models with a standard surface finish (Ra 0.8), as well as polished and electropolished versions for the most demanding applications.

The use of a suitable stainless steel manway in a food plant ensures:

• safe access to the inside of the tank, equipment, pipeline,
• durability and convenience of use and washing,
• high resistance to corrosive, chemical and temperature factors,
• highly aesthetically pleasing appearance.

A whole range of equipment is involved in food production processes, in which stainless steel manways are an indispensable part of the equipment. Most recognizable among them are tanks of all types – including mixers, fermenters, autoclaves and many others. Another group includes drying chambers and other types of thermal processing equipment. Beverage bottling and storage processes require intermediate tanks and large-capacity storage tanks (including those equipped with thermal insulation), as well as appropriate systems for temperature change and control. Stainless steel manways are also installed in silos for storing bulk materials (for example, grains and cereals).

Each of the above applications entails the need for a manway with appropriately adapted parameters, shape and functionality. Therefore, we distinguish the following types of manways:

• round,
• oval (elliptical),
• rectangular (including square).

The diameters of round manways (including the smallest ones sometimes referred to as manway covers), are usually in the range from DN100 to DN1400. The length of the longer side of an elliptical manway usually ranges from 250 mm to 500 mm, but designs as long as 800 mm are also available.

Rectangular manway covers, like round ones, are manufactured in a wide range of sizes – both those whose longer side is less than 300 mm long and those where the side length reaches 2000 mm.

Why is it so important to properly finish the surface of manways, in particular those parts that are in direct contact with the working medium? The answer lies in the aforementioned food safety standards and our health. Smooth surfaces reduce the possibility of product particles settling and deposited in cavities, which would promote the proliferation of harmful organisms that threaten food quality. The non-stick qualities of polished stainless steel facilitate cleaning and make the process much more efficient. They also reduce the use of cleaning agents, which translates into concrete economic effects.