Pipes and fittings

Pipes and fittings

The pipe system

The product flows between the components of the plant in the pipe system.

A dairy also has conduit systems for other media such as water, steam, cleaning solutions, coolant and compressed air. A waste-water system to the drain is also necessary. All these systems are basically built up in the same way. The difference is in the materials used, the design of the components and the sizes of the pipes.

All components in contact with the product are made of stainless steel. Various materials are used in the other systems, e.g. cast iron, steel, copper and aluminium. Plastic is used for water and air lines, and ceramic for drainage and sewage pipes.

The following section deals only with the product line and its components. The pipe systems for service media are described in the section dealing with utility installations.

The following types of fittings are included in the product pipe system:

• Straight pipes, bends, tees, reducers and unions
• Special fittings such as sight glasses, instrument bends, etc.
• Valves for stopping and directing the flow
• Valves for pressure and flow control
• Pipe supports

Connections

Permanent joints are welded, figure 6.8.1. Where disconnection is required, the pipe connection is in the form of a threaded union with a male end and a retained nut with a joint ring in between, or a clamped union with a joint ring, figure 6.8.2.

The union permits disconnection without disturbing other pipework. This type of joint is therefore used to connect process equipment, instruments, etc. that need to be removed for cleaning, repair or replacement.

Different countries have different union standards. These can be SMS  (Swedish Dairy Standard) also used internationally, DIN (German), BS (British), IDF/ISO* and ISO clamps (widely used in the US).

Bends, Tees and similar fittings are available for welding, and with welded unions. In the latter case, the fitting can be ordered with nut or male ends or with clamp fittings.

All unions must be tightened firmly to prevent liquid from leaking out or air from being sucked into the system and causing problems in downstream parts of the process.

Special pipe fittings

Sight glasses are fitted in the line where a visual check of the product is required.

Bends with instrument connections are used for fitting instruments like thermometers and gauges. The sensor should be directed against the flow to make readings as accurate as possible. The connection boss can also be used for a sampling cock. Instrument connections can also be provided with welding special bosses directly on to the pipe during installation.

Sampling devices

Sampling devices need to be installed at strategic points in the plant to collect product samples for analysis. For quality control, such as determining the fat content of milk and the pH value of cultured products, the samples can be collected from a sampling cock, figure 6.8.3.

For hygienic quality tests, the sampling method must preclude any risk of contamination from outside the pipe. A sampling plug can therefore be used. This plug, shown in figure 6.8.4, has a rubber bung at the bottom. The plug is first removed and all parts that could contaminate the sample are sterilised (typically a wad moistered in a chlorine solution just before sampling), after which the needle of a hypodermic syringe is inserted through the bung into the product, and a sample is withdrawn.

Samples of aseptic products heat treated at such a high temperature that they are sterile are always collected through an aseptic sampling valve to avoid reinfection.

Pipe supports

Pipes usually run about 2 3 metres above the dairy floor. All components must be easily accessible for inspection and maintenance. The lines should slope slightly (1:200 1:1000) to be self-draining. There should be no pockets at any point along the line where the product or cleaning fluid can collect.

Pipes must be firmly supported. On the other hand the pipes should not be so restrained that movement is prevented. The pipes will expand considerably, when the product temperatures are high and during cleaning. The resulting increase in length and torsional forces in bends and equipment must be absorbed. This, plus the fact that the various components make the pipe system very heavy, place great demands on accuracy and on the experience of the system designer