Food processing, pharmaceuticals manufacturing, and biological research processes are naturally sensitive to the presence of micro-organisms such as bacteria, fungi, and algae. It is important in these processes to ensure the absence of harmful micro-organisms, for reasons of both human health and quality control. For this reason, the process piping and vessels in these industries is designed ﬁrst and foremost to be thoroughly cleaned without the need for disassembly. Regular cleaning and sterilization cycles are planned and executed between production schedules (batches) to ensure no colonies of harmful micro-organisms can grow.
A common Clean-In-Place (CIP) protocol consists of ﬂushing all process piping and vessels with alternating acid and caustic solutions, then washing with puriﬁed water. For increased sanitization, a Steam-In-Place (SIP) cycle may be incorporated as well, ﬂushing all process pipes and vessels with hot steam to ensure the destruction of any micro-organisms.
An important design feature of any sanitary process is the elimination of any “dead ends” (often called dead legs in the industry), crevices, or voids where ﬂuid may collect and stagnate. This includes any instruments contacting the process ﬂuids. It would be unsafe, for example, to connect something as simple as a bourdon-tube pressure gauge to a pipe carrying biologically sensitive ﬂuid(s), since the interior volume of the bourdon tube will act as a stagnant refuge for colonies of micro-organisms to grow:
Instead, any pressure gauge must use an isolating diaphragm, where the process ﬂuid pressure is transferred to the gauge mechanism through a sterile “ﬁll ﬂuid” that never contacts the process ﬂuid:
With the isolating diaphragm in place, there are no stagnant places for process ﬂuid to collect and avoid ﬂushing by CIP or SIP cycles.
Standard pipe ﬁttings are problematic in sanitary systems, as tiny voids between the mating threads of male and female pipe ﬁttings may provide refuge for micro-organisms. To avoid this problem, special sanitary ﬁttings are used instead. These ﬁttings consist of a matched pair of ﬂanges, held together by an external clamp. An array of sanitary ﬁttings on an instrument test bench appear in the following photograph:
The next photograph shows the installation of a pressure transmitter on an ultra-pure water line using one of these sanitary ﬁttings. The external clamp holding the two ﬂanges together is clearly visible in this photograph:
Sanitary pipe ﬁttings are not limited to instrument connections, either. Here are two photographs of process equipment (a ball valve on the left, and a pump on the right) connected to process pipes using sanitary ﬁttings: