Reader feedback: August 2018

Aug. 23, 2018
In August's Control reader feedback, readers respond to Joe Weiss' Unfettered blog as well as May's Ask the Experts

Regarding Joe Weiss’ “Unfettered” blog [2018 RSA Conference observations and the dangerous lack of control system understanding by network security personnel], even if a security engineer works for a vendor organization, it doesn’t necessarily mean he/she has a process control background. New hires generally have an IT security background because people with a process control background are very difficult to find. Within the vendor organization, the security team will not be very popular if they hire people away from the service or engineering departments.

As a result, many cybersecurity and risk assessments are conducted by people that have no understanding of the system they're investigating, and miss several serious issues. Some walk away after a one-day discussion on back-ups, antivirus, firewall, etc. without collecting information, without investigating all these other functions in an ICS. Others are considered high-cost because they want to do a thorough and complete job. It's very difficult for a plant to select the right service/partner—and a SANS certification is not really a good measure because it also addresses a small part of the scope.

I have seen reports of very respectable companies really missing the issue, for example, going in auto mode if they find an OPC connection and advising a firewall, even if the OPC server has service-wide setting for read/write access. Only OT specialists know the restrictions of OT applications, and how to fix the vulnerabilities.

Sinclair Koelemij
[email protected]

Having spent the better part of my career in the polymer industry around reactors, I would like to add a few points to the article “Polymer reactor level measurement” (Is it wise or dangerous to back up differential pressure with nuclear instrumentation?)

  1. Residence time in a polymer reactor is really measured on a mass basis rather than volumetric basis (i.e., reactor mass divided by mass flow). This may not be important in reactor systems that maintain constant density, but it's significant in boiling reactor systems where density varies due to vapor bubbles in the mixture. In reactor systems such as these, DP level detection is preferred because it related to mass above the lower detector, and therefore compensates for density differences by its nature. Nuclear detectors, on the other hand, show actual level and will vary as the reactor boiling varies, even though residence time is not changing. This leads to errors in level control.
  2. Some polymer reactors use load cells for maintaining level since mass is the critical variable.
  3. An effective way to keep DP level instruments from plugging up is to take a small slipstream of the reactor feed, and use it to continuously purge the port for the lower DP instrument where it goes into the reactor. This can be accomplished by installing a slim ring with a port between diaphragm and the reactor nozzle. As long as the purge is maintained at a low rate (2 GPH), the backpressure is minimal and the level measurement will not be affected.
  4. Nuclear detectors are very effective, and are used routinely in high-temperature/high-viscosity situations, such as polymer devolatilizer vessels. Other level detectors have issues with this environment.

Mark Cicerchi
[email protected]

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