Using the piping inspection RAGAGEP API 570, one of the first steps in our piping inspections/testing is to establish the “Class” our piping fits into. In most cases, I advise my clients to classify their PSM/RMP-covered piping as Class 1. However, there is a possibility that some flammable liquid piping could be classified in a lower class (although I would never recommend it). This came up with a newly built process, and I thought I would use their discussion as a teachable moment.
The argument was to classify their flammable liquids piping as Class 2 rather than Class 1. The differences between these classes can lead to significant reductions in inspection/testing frequency, which drives much of the debate. Had this been a small system/process (e.g., NOT covered under PSM), I would have agreed, as their flammable liquid clearly met the Class 2 definition.
API 570 states the following regarding how we establish the piping class, which then dictates the frequency and extent of inspections.
The frequency and extent of inspection on piping circuits whether above or below ground depend on the forms of degradation that can affect the piping and consequence of a piping failure. The various forms of degradation that can affect process piping circuits are described in API 571 in more detail. A simplified classification of piping based on the consequence of failure is defined in 6.3.4. As described in 5.3, inspection strategy based on probability and consequence of failure is referred to as RBI.
The simplified piping classification scheme in 6.3.4 is based on the consequence of a failure. The classification is used to establish frequency and extent of inspection. The owner/user may devise a more extensive classification scheme that more accurately assesses consequence for certain piping circuits. The consequence assessment would consider the potential for explosion, fire, toxicity, environmental impact, and other potential effects associated with a failure. Reference API 580 Assessing Consequence of Failure guidelines and requirements. After an effective assessment is conducted, the results can be used to establish a piping circuit inspection strategy and define the appropriate inspection plan per 5.2
Here are the definitions of the Piping Classes:
Class 1
Services with the highest potential of resulting in an immediate emergency if a leak were to occur are in Class 1. Such an emergency may be safety or environmental in nature. Examples of Class 1 piping include, but are not necessarily limited to, those containing the following.
a) Flammable services that can auto-refrigerate and lead to brittle fracture.
b) Pressurized services that can rapidly vaporize during release, creating vapors that can collect and form an explosive mixture, such as C2, C3, and C4 streams. 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).
c) Hydrogen sulfide (greater than 3 % weight) in a gaseous stream.
d) Anhydrous hydrogen chloride.
e) Hydrofluoric acid in main and trace acid services per API RP 751.
f) Piping over or adjacent to water and piping over public throughways (refer to national or local regulations e.g. Department of Transportation and Coast Guard for inspection of over water piping).
g) Flammable services operating above their auto-ignition temperature.
Class 2
Services not included in other classes are in Class 2. This classification includes the majority of unit process piping and selected off-site piping. Typical examples of these services include but are not necessarily limited to those containing the following:
a) on-site hydrocarbons that will slowly vaporize during release such as those operating below the boiling point but above the flash point,
b) on-site hydrogen, fuel gas, and natural gas,
c) on-site strong acids and caustics.
Class 3
Services that are either flammable but do not significantly vaporize when they leak, (i.e. below the flash point), or flammable but are located in remote areas and operate below the boiling point are in Class 3.
Services that are potentially harmful to human tissue but are located in remote areas may be included in this class.
Examples of Class 3 service include, but are not necessarily limited to, those containing the following:
a) on-site hydrocarbons that will not significantly vaporize during release such as those operating below the flash point;
b) off-site distillate and product lines to and from storage and loading;
c) tank farm piping;
d) off-site acids and caustics;
e) off-site hydrogen, fuel gas and natural gas; and
f) Other lower risk hydrocarbon piping that does not fall in Class 1, 2, or 4.
Class 4
Services that are essentially nonflammable and nontoxic are in Class 4, 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 service include, but are not necessarily limited to, those containing the following:
a) steam and steam condensate;
b) air;
c) nitrogen;
d) water, including boiler feed water or stripped sour water;
e) lube oil, seal oil;
f) ASME B31.3, Category D services*;
g) plumbing and sewers.
*Category D services under ASME B31.3 are the least hazardous classification for a piping system, covering fluids that are nonflammable, non-toxic, and safe for human tissues, with a design pressure not exceeding 150 psi and a design temperature between -20°F and 366°F. Examples include potable water, instrument air, and heating/cooling systems, which are subject to less stringent design, inspection, and testing requirements compared to other categories.
As we can see, a flammable liquid with a Flashpoint of less than 100°F could be put into a Class 2 piping circuit, which means the piping needs:
- Thickness Measurement at least every 10 years (vs. 5 years for Class 1)
- Visual External at least every 5 years (same as Class 1)
Given that the costs of piping inspections are driven by NDE/NDT every 5/10 years, a business would prefer the 10-year schedule over the 5-year one. This results in significant cost savings for the business. But is it the right Process Safety decision?
As I mentioned earlier, I classified all my PSM-covered piping as Class 1. This is based mainly on the consequences of an LOPC event involving the piping, and also on the available flammable volume for the LOPC event.