API RP 500 Fig. 104 vs. Fig. 53

[CGC Texas]

This may seem like a mundane question - but the answer seems to differ from company to company.

I would really appreciate someone clarifying for me when Fig. 104 radius of 25'-0" overrides say Figure 53 as example of 10'-0" radius.

Compressor run at an obviously higher pressure than 275 PSIG....therefore shouldn't the radius be 25'-0"?

Also I am in discussion with several electrical engineers regarding Fig. 104 and the use of this Figure. A source could be considered the pipe in the piperack with various fittings for pressure and temperature, would this not require the piperack to be rated at 25'-0"?

I work quite frequently on natural gas compressor stations and treating facilities - the answers to these questions seem to vary from company to company and client to client.

I would really, REALLY appreciate some clarifications on this. I even tried contacting the API for assistance and they could not help me, nor could they recommend training anywhere on the API RP500. That really surprised me.

Are we left to interpret this? Is there any definitive answer?

Any and all assistance would be much appreciated.

CGC in Texas

 

[rbalex]

Have you read and evaluated the figure's titles, notes, and referenced sections (14.3.8 and 10.9.2) and reviewed them in context of their associated chapters?

Chapter 14 RECOMMENDATIONS FOR DETERMINING DEGREE AND EXTENT OF CLASSIFIED LOCATIONS AT PETROLEUM PIPELINE TRANSPORTATION FACILITIES

Chapter 10 RECOMMENDATIONS FOR DETERMINING DEGREE AND EXTENT OF CLASSIFIED LOCATIONS AT DRILLING RIGS AND PRODUCTION FACILITIES ON LAND AND ON MARINE FIXED PLATFORMS
​

Personally, I prefer Appendix D for a more analytical approach.

 

[hazloc2002]

Please, note that area classification is related with gas dispersion, ventilation... these disciplines are not familiar to electrical engineers. So, electrical engineers are not the best option to debate such topic. The great danger that API RP 500 and 505 may induce to users is that area classification is simply a "copy and paste" action that can be performed by anyone. A careful reading of the note in E.1, Appendix E of API RP 505:1997 emphasizes this.
Also, the note shown under many figures, as example in 23 "distances given are for typical refinery installations.. ", should be written in a similar way under all figures, because the figure is the final result of the considerations for that particular situation. So, we need to know what was considered for the figure, to compare to what we have in our case, and then, decide if the figure can be applied without modifications in our case, or if it will need to be modified.
This is what is expected in an area classification study.
This maybe explain why there is not only one answer for classifying "a compressor installation".


Another interesting reading is the 3rd paragraph of the Foreword section of API RP 505:1997.

 

[rbalex]

Interestingly enough, while electrical engineers many not be "...the best option to debate such topic," they make up 100% of the API 500/505/540 Working Group. This is not particularly unusual. Engineers often expand their areas of expertise beyond their original discipline; usually because it becomes necessary.

As far as the disclaimer in the forward, you will find similar content somewhere in virtually any technical organization's documents. Something to the effect: "You can use our stuff if you want to - we don't make any guarantees." This applies even when such documents become statutory; e.g., see the NFPA disclaimer on the second page of the 2008 NEC.