Does a logic diagram need to be created by a design institute?

The data sheets for the instruments, the high/low alarm values and interlock values for the DCS and SIS systems, as well as the logic diagrams for the interlocks – these should be provided by the design institute

I’ve never heard of chemical engineering projects requiring logic diagrams; no chemical engineering design firm does that. Stop being naive – at most, what’s produced are interlock logic diagrams, complex circuit control diagrams, and sequence control diagrams.

Thank you; I just thought I was an amateur, which is why I asked! According to what you said, the interlocking logic diagram still needs to be drawn by a design institute, right?

This post was last edited by ZhiGE on 2019-12-11 at 13:29. 1. In SHSG-053-2011–Provisions for the Detailed Engineering Design of Petrochemical Plants: 8 Instruments – Items to be provided by the instrument design institute. 2. Since it’s a new project, one should look at the specifications and standards, as well as the project management documents. A. Project construction includes five phases: project consulting, project design, project procurement, project construction, and project commissioning. B. Engineering design can be divided into up to six stages: process package design, conceptual design, front-end engineering design (FEED), basic design, detailed design, and as-built drawing design. Try to look up the regulatory requirements for each stage. It’s better to rely on oneself than to ask others for help.

A logic diagram is necessary; otherwise, I can build a device for you, but if I don’t know how to control it, what’s the use of that?

I have been working in design for eleven years; the designs for new installations are all prepared by the design institute. Except for some technical improvement projects, sometimes the equipment manufacturers provide their own logic diagrams, and in those cases we don’t bother to create our own designs and simply proceed with construction using the information provided by the manufacturers.

It may or may not be included, depending on how the contract is drafted. Sometimes, even though the design institute provides a logic diagram, the DCS manufacturer’s staff may not look at it when working on the system; instead, they will request a written version of the interlock instructions from the client, and use that to set up the interlocks in the system

The design depth of the interlock logic diagram includes this. Another design institute must provide it as well; nowadays, the requirements for chemical safety are very strict, and many external inspections require this document along with the commissioning records. Many design institutes produce designs with unclear logical relationships; they only manage to convey a general idea. Many large design institutes abroad, as well as some excellent design institutes in China, can produce very accurate results; for example, in DCS, positive logic is used for triggering, with OR operations applied to multiple conditions, along with functions for reset and bypass. In SIS, negative logic is used for triggering, with AND operations and functions for obtaining the inverted value. In many design institutes, the DCS and SIS logic are made identical. System manufacturers, having experience in this field, understand what is required; however, interlock logic must still be developed. The requirements for safety checks are unreasonable – it would be sufficient for the process team to communicate directly with the manufacturers.