Natural Gas Pipeline Pressure Protection

[RPG]

Does anyone know if their are specific requirements for Safety Integrity Systems (Interlocks) to control the pipeline pressure of natural gas below the rating of the transmission piping systems. I have found no specific requirements saying anything other than you need to protect against overpressure. Can the safety system reside in the same PLC used for control? My understanding is that the system in question falls under the auspices of DOT and not OSHA.

 

[ICman]

I haven't seen any references to SIS in our industry. DOT, along with industry Standards (ASME, API, ISA, NFPA, etc.) pretty much set the requirements.

You can implement the safety system in your control system, but you must have local safety backup devices in place. For instance, a relief valve or monitor or high-pressure override connected to a positive shutoff valve must be installed on the pipeline.

The control system (PLC, DCS, other) serves as a primary device to avoid the condition. It might close the PSO valve to isolate the line when pressure increases above a setpoint. A separate pressure switch would also close that valve, perhaps at a higher setpoint, in case the control system failed.

My company uses some PLC-based safety systems on compressor installations, mostly for fire or gas detection. These systems are almost always separate from the process control system. Many are redundant and/or have "voting" capabilities.

 

[dcasto]

Just out of curiosity, are you the operator of the DOt regulated pipeline? It is the pipeline operators responsibility to protect the pipeline, not the supplier.

Go to this site for the regulations:

http://www.access.gpo.gov/nara/cfr/waisidx_03/49cfrv3_03.html

 

[RPG]

I represent an engineering firm working for the operator of the pipeline. I am familiar with the DOT regulation, they do not specify the "integrity" of the safety system that is required to protect the pipeline or whether it must meet any specific criteria. If this was a chemical process covered under OSHA 1910.119 I would have a better "feel" for how the safety system should be designed.

 

[dcasto]

DOT is not persciptive on SIS, neither is OSHA for that manner. DOT states that you must write down the companies plan for overpressure protection and test or inspect the plan annually (perscriptive). Also, DOT see's more problem with secrurity of the system since most pipelines are unattended. The best PLC with interlocks can be defeted with a snip of the wires out in the middle of a field. Again, DOT wants a documented plan.

Go ahead and make your plan follow ISA standards, but if you miss one point in the standard, DOT will leavy a fine for not following the plan to the letter.Bottom line, the simpler, the better too. A relief valve with chains and locks are pretty reliable and a simple plan.