As I continue my efforts to educate the safety profession in process safety and, more specifically, on the differences between welded pipe joints versus flanged pipe joints, this topic usually comes up. The big question that is the 800-pound gorilla in the room is…
If both welded and flanged joints are allowed in our flammable liquid processes, then why does NFPA 497 only make an exception for welded joints; but not for flanged joints?
First, let’s review what NFPA 497 says about electrical classifications where a “flanged joint” is present.
Please remember, although I have placed this article in my Chemical Process Safety Category, this topic/requirement applies to all flammable liquid processing, not just those over 10,000 pounds. I have simply chosen to keep all my posts regarding electrical classifications in a single category.
(emphasis by me)
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5.5 Unclassified Locations. 5.5.1 Experience has shown that the release of ignitible mixtures from some operations and apparatus is so infrequent that area classification is not necessary. For example, it is not usually necessary to classify the following locations where combustible materials are processed, stored, or handled: (1) Locations that have adequate ventilation, where combustible materials are contained within suitable, well-maintained, closed piping systems (2) Locations that lack adequate ventilation, but where piping systems are WITHOUT valves, fittings, FLANGES, and similar accessories that may be prone to leaks (3) Locations where combustible materials are stored in suitable containers (4) Locations where the use of combustible liquids, or flammable liquids or gases, will not produce gas or vapor sufficient to reach 25 percent of the lower flammable limit (LFL) of that combustible material |
As we can see, NFPA 497 5.5.1 (2) states that where we have flanges, the area would need to be evaluated for its electrical classification.
So if the pipe passing through an area has welded joints (including the valves are welded into place) AND the area has “adequate ventilation”, the area is one that would not have to be a Class 1 area.
But if we take that same pipe run and its joints are flanged, we could NOT use 5.5 as a means to state the area can be without electrical classification.
Why is this? Are welded joints have that much better integrity than flanged joints?
If we were to take two NEWLY installed pipe runs, one with welded joints and one with flanged joints, at the time of installation – BOTH would pass a PRESSURE TEST and a LEAK TEST, making them EQUAL at the time of their installation. However, where RISK CREEPS in, is when that joint has to be broken and put back into service. A welded joint will require a qualified welder, pressure test, and leak test to be put back into service, whereas many facilities with flanged joints will have a maintenance tech (usually underqualified with no procedure and no torque wrench) put the flanged joint back together and into service. Often, these flanged joints do NOT receive pressure and leak tests before they are returned to service.
Of course, the welded joints could be returned to service without any pressure testing or leak testing in violation of B31 series, but even then, if the welding was done per ASME Section IX and B31.3, the QUALITY of the work is much higher than a flanged joint being returned to service by unqualified personnel with no procedure or torque wrench.
And, of course, if the facility threw all caution into the wind and allowed an unqualified welder to make the joint, did not make the weld per a Welding Procedure Specification (WPS), which also excluded any visual examination of the weld and no testing is performed, then that work would equal the flanged joint that was also put together under highly questionable circumstances. But if we consider this a reality, why are we even discussing Electrical Classifications? As I will bet a burger and a beer, a facility that is not meeting the fundamentals of ASME B31 for their piping certainly isn’t worried about the consequences when that piping leaks.