Path Confirmation

To confirm that the flow path is properly set, there is typically a requirement
for feedback on solenoid valves and any transfer panel positions.
This is important to ensure personnel safety, as well as effective steaming.
Proximity switches are commonly used for path confirmation, as indicated
in the sections below, as they are somewhat more reliable than limit
switches.

For valve feedback, screw-on "switch-packs" are available from a variety of
vendors. Some of these are self-adjusting, eliminating one common cause
of reliability problems. Be sure to discuss the reliability of valve feedback
systems with maintenance personnel. They can provide insight into what
works in your plant.

Instrumentation and automation personnel should pay close attention to
the design of transfer panels to ensure that the switches will provide foolproof
confirmation of path.

Temperature

The most important measurements of the SIP operation are, of course,
temperature measurements. Temperature is the measurement used to confirm
the completion of the SIP step.

Proper placement of temperature measurements is key to the success of
the SIP automation. In addition to the temperature measurements that
are in place for process purposes, the system must typically measure temperature
at all representative locations, as well as measure and confirm the
temperature at the coldest points of the system being steamed. Consult
heavily with validation, quality, and regulatory personnel to determine
the appropriate number and location of sensors.

To hold costs down, and to minimize the blockage of small piping, thermocouples
are most often used for temperature measurement throughout
the SIP operation. Quite often, the coldest points of measurement are just
prior to steam traps located at the ends of small sample lines or drain
lines. These may be very small diameter tubing, and even a small thermocouple
may restrict steam and condensate flow.

Pressure

There are two uses of pressure measurement during SIP. The first occurs
during "air pressure hold," and the second ensures proper steam pressure
during steaming.

For air pressure hold, the valves are set for steaming, then pressurized with
dry air or other non-condensable gas. If the system can hold pressure,
then it is ready for steaming.

Designing for air pressure hold can present a challenge. This is because
you must be able to measure pressure for each flow path or circuit. Careful
study of a P&ID, with each steam flow path highlighted, will help to
determine where to locate the pressure measurements.

Generally, SIP cycles try to meet a temperature of 121°C or higher. This
means that you must supply steam under pressure. While it is not an
absolute requirement to measure and control pressure to achieve this temperature,
it is a very good idea to include pressure measurement at least in
each vessel being steamed.

Steam Flow

Measuring steam flow is generally not required. However, for steaming of
large vessels or systems, this may be a useful measurement. Generally,
steam flow measurement can be placed upstream of sterile isolation
filters, simplifying the design requirements.