Dairy Engineering

Module 1. Sanitary pipes, fittings and milk handling equipment

Lesson 3
INSTALLATION, CARE AND MAINTENANCE OF PIPES & FITTING

3.1 Introduction

Pipelines in dairy industry are of two types, i.e. those which are coming in contact with the milk and milk products, and those which are mainly of service pipe lines. Though we will be considering here only those which are coming in contact with milk and milk products, some of the basic principles will be same.

3.2 Installation

Well-designed piping systems require a plant layout that provides adequate space around equipment to ensure that the piping and associated valves are arranged in an operable and maintainable fashion, with minimal intrusion into operators’ space. Such conditions should be a part of the building’s design from its conception. A systematic approach to layout produces a workable end result. The end result should reflect due consideration for the construction, operation, and maintenance factors for every piece of equipment involved.

The first step in installation is to draw the Piping and Instrument diagram (PID) showing the arrangement of the process equipment, piping, instruments, valves and other fittings. It should include:

1. All process equipment, identified by an equipment number. This should be drawn roughly in proportion and the location of the equipment.
2. All pipes, identified by a line number. The pipe size and material should be shown.
3. All valves control and block valves, with an identification number and size should be shown.
4. Ancillary fittings that are part of the piping system, such as inline strainers, steam traps, with an identification number.
5. Pumps, identified by a suitable code number
6. All control loops and instruments, with an identification number.

The Piping and instrument diagram will resemble the process flow sheet. When the diagram is laid out, it is necessary to show the relative elevation of the process connections to the equipment where they affect the process operation; for example, the Net Positive Suction Head (NPSH) of pumps, barometric legs, siphons. Full details of pipe layout are usually shown in a different drawing, known as Piping Isometric Drawing. In all the drawings, standard symbols for the valves, instrument lines etc. should be used. Sloping of lines should ensure complete draining. Sloping of lines of 0.3 to 0.5% is sufficient for post cleaning and gravity flow of low-viscosity fluids.

3.2.1 Sizing of pipe lines

Over sizing pipelines increases installation costs, and under sizing increases pressure drop. It is important to know the distinction between pipe and tube here. For tubes, inside diameters vary according to specified schedule or wall thickness; whereas pipes are labeled by their nominal bore, sanitary tubing is labeled by its outside diameter, and has a smaller bore. For example, a 2” stainless steel pipe has an outside diameter of 2.375”, and if made of schedule 10S has a resultant bore of 2.157”. A 2” sanitary tube has an outside diameter of 2.000” and a 0.065” wall thickness, for a resultant bore of only 1.870”. This reduction in available diameter, if overlooked, could be crucial in flow calculations.

The size of the suction pipe of pump should never be smaller than that of the discharge pipe; usually it is one size larger.

3.2.2 Connections

Commonly used methods are flanged connections, welded fittings, and threaded couplings. The important aspect is that these should not only be effective, but also should be easy for cleaning and sterilization. It should not have any cavities that cannot be cleaned. The pockets caused by branches in pipelines should not be more than 6 times the diameter. Preferences are being shown for the welding of pipes and fittings utilizing inert gas to reduce the number of pipe unions so as to minimize potential of crevice areas, which are difficult to clean.

As far as feasible, valves, filters, excessive fittings, horizontal bends, elbows and tee joints should be avoided close to the suction side of the pump.

3.2.3 Valves

Most of the valves installed in plants are used for isolation service, usually referred to as Block valves, to prevent unwanted flow past a given point in a piped system. The remainder are used to control either rate of flow or pressure of the flowing medium, at a particular point in the system, referred to as throttling or Control Valves. The body shapes of Gate and Globe valves render them unclean-able and thus potential sources of contamination. The alternative valve involves a choice between ball, butterfly or diaphragm valves. The ball is frequently favoured because its valve stem is isolated from fluid; it has a quarter-turn operation, and is suitable for CIP cleaning.

3.2.4 Supports

The tubing should be supported at regular intervals, near valves and to all changes in direction. Materials used for hanger components and floor stand supports should be of stainless steel to avoid external corrosion and galvanic action between dissimilar materials. Rubber insert pads may be used to isolate tubing from the support to reduce vibration. Rigid anchoring should be replaced by floating supports which avoid distortion of tubing systems due to temperature changes.

Table 3.1 Spacing for support of pipe

Size (mm)	Distance between supports (m)
50	2.4
75	3.4
100	4.0
125	4.5

3.3 Requirements in Pipe Lines

The pipelines should be clean, free from longitudinal grooving, both inside and outside, should be smooth, free from surface defects, straight, cylindrical in shape when viewed from end, uniform in thickness.

3.4 Instruments & Fittings

Instruments should be made from materials considered safe for direct contact between the flowing media and the instrument itself, preferably highly polished 316L ( grade 316 with <0.04% carbon) stainless steel. The instrument should be connected at point of maximum turbulence and not near stagnant pockets. Connections of pipe should avoid cavities or pockets likely to encourage accumulations of solids.

3.5 Maintenance of Pipes & Fittings

1. Worn-out gaskets in pipeline joints should be replaced periodically, before they become brittle, deformed or loose their shape permanently.
2. During preventive maintenance inspection, distress cracks on walls and footings near the pipe anchors will indicate improper layout with regard to thermal expansion.
3. Check for the supports of the pipelines, whether they firm or if they are dislodged from their installed positions.
4. Check if vibrations, expansions caused by the process equipment like homogenizer, Pasteurizer are prevented from being carried on to pipelines connected to them.
5. Check, if any modification done like expansion, shifting of equipment are not affecting the pipeline installation, and properly supported and connected without any stresses.