How did you “Class” your PSM/RMP covered process piping?

For those living the dream of being a process safety professional know that one of the fundamental decisions we eventually have to make is how will we “class” our PSM/RMP covered process piping.  For almost all of us, the best Piping Inspection RAGAGEP will be API 570, Piping Inspection Code and this RAGAGEP has a very ingenious way of “classifying” process piping based on its content and a degree of hazard.  But like many RAGAGEPs, it provides us “guidance” and this opens the door to questions and incorrect decisions.  In this article, I hope to convince you that our PSM/RMP covered process piping should land in Class 1.

So API 570 has four (4) classes of piping, Class 1-4, with the higher risk piping falling into the lower numbers – meaning Class 1 is the most hazardous and Class 4 is the least hazardous.  Here is an explanation of the classes and some examples of such piping as noted by API.

Class 1 piping is described as 

“the highest potential of resulting in an immediate emergency if a leak were to occur”. Such an emergency may be a safety or environmental in nature.

Examples of Class 1 piping include, but are not necessarily limited to those containing the following:

1. Flammable services that can auto-refrigerate and lead to brittle fracture.
2. Pressurized services that can rapidly vaporize during release, creating vapors that can collect and form an explosive mixture. Fluids that can rapidly vaporize are those with atmospheric boiling temperatures below 50°F (10°C) or where the atmospheric boiling point is below the operating temperature (typically a concern with high-temperature services).
3. Hydrogen sulfide (greater than 3% weight) in a gaseous stream.
4. Anhydrous hydrogen chloride
5. Hydrofluoric acid.
6. Piping over or adjacent to water and piping over public throughways (refer to Department of Transportation and U.S. Coast Guard regulations for inspection of over water piping).
7. Flammable services operating above their auto-ignition temperature.

Class 2 piping is sort of a landing place for piping that is not included in other classes. Typical examples of these services include but are not necessarily limited to those containing the following:

1. on-site hydrocarbons that will slowly vaporize during release such as those operating below the flash point,
2. hydrogen, fuel gas, and natural gas,
3. on-site strong acids and caustics.

Class 3 piping is for flammables that do not significantly vaporize when they leak and are NOT located in high-activity areas or service that is potentially harmful to human tissue but are located in remote areas may be included in this class. Examples of Class 3 piping include but are not necessarily limited to those containing the following:

1. on-site hydrocarbons that will not significantly vaporize during release such as those operating below the flash point;
2. distillate and product lines to and from storage and loading;
3. tank farm piping;
4. off-site acids and caustics.

Class 4 piping are essentially nonflammable and nontoxic, as are most utility services. Inspection of Class 4 piping is optional and usually based on reliability needs and business impacts as opposed to safety or environmental impact. Examples of Class 4 piping include, but are not necessarily limited to those containing the following:

1. steam and steam condensate;
2. air;
3. nitrogen;
4. water, including boiler feed water, stripped sour water;
5. lube oil, seal oil;
6. ASME 831.3, Category D services;
7. plumbing and sewers

As you can see, we have four (4) classes for our piping to land in and the final decision is 100% ours; however, we need to be able to defend/rationalize our final decision.  Of course, it is easiest to state our PSM/RMP covered process piping will fall into Class 1, but this comes with additional responsibilities and activities.  And of course I would agree with your decision 100%; but what does it mean to put our piping into Class 1?

Inspection Frequencies are based on Classification of Pipe Circuit(s)

API 570 has established inspection frequencies based on the Class of piping…

NOTE:  I have not included ALL of Table 2 above, just Class 1-3.

As we can see, there is a significant difference in the frequency of “Thickness Measurements” between Class 1 and Class 2 piping.  It is these “Thickness Measurements” that drive the costs of most MI Inspection/Testing programs, so merely placing your piping into Class 1 would increase your MI costs substantially!  I am not one to play the cost games, as I am planted firmly in the camp that all PSM/RMP piping belongs in Class 1, but that is merely my opinion and I have been swayed a time or two over the past 20 years to put some PSM/RMP piping in Class 2.  

Bottom line, our PSM/RMP covered process piping needs to be inspected/tested per an RAGAGEP.  The best piping inspection RAGAGEP is API 570.  API 570 classifies our process piping into one of four categories.  Which “class” we choose for our piping circuits MUST be documented if we choose a class other than Class 1.  I can not end without mentioning Risk Based Inspection (RBI) protocol, as it is this protocol that will guide us to establish inspection frequencies that differ from those shown in the table above.  

I can not end without mentioning Risk Based Inspection (RBI) protocol, as it is this protocol that will guide us to establish inspection frequencies that differ from those shown in the table above.  But user beware… RBI should be reserved for a very mature MI program and should not be attempted by those not well versed in risk management.

Lastly, be very careful trying to justify your piping does not belong in Class 1 merely because your specific HHC/EHS is not one of the “examples” that API list.  We MUST use the “characteristics” that define Class 1 piping and assess our HHC/EHS’s against these characteristics.  But each facility has the final say – just document the rationale used and follow your inspection plans – most importantly the inspection frequencies – and we should have a low probability of an LOPC event and maybe even make OSHA/EPA happy.