Plumbing 101 : Enlightening the application of standards in relation with brass parts
By Isabelle Murray P. Eng., M.A.Sc., Metallurgist, Assistant Manager, Montreal, Frédéric Bourgeois Eng., M.A.Sc., Metallurgist,
Brass parts are commonly integrated to modern commercial, industrial and residential plumbing systems. Such parts are, in fact, installed in water, gas or fuel oil plumbing networks. It has been recently noted that various brass parts installed in water plumbing networks are subject to a high failure rate.
Such brass parts must nevertheless rigorously comply with various international and national standards criteria. We, however, noted a significant increase in the failure rate of brass parts exposed to water in plumbing networks.
To better understand this problem, we will first present an outline of the various standards' criteria that are commonly applied to brass plumbing parts manufacturing. We will then identify the main criteria applied to the manufacturing of ball valves and plumbing fittings installed in PEX plastic plumbing networks. We will then
analyze various failure characteristics in relation with some standards' criteria. We will finally demonstrate in this paper the degree of confusion that can arise from the interpretation of some of these standards' elements or criteria.
Standards review and outline
Several water plumbing network breakdowns, as well as damage generated by ensuing leaks, are caused by the premature failure of brass ball valves. These valves are generally bearing "WOG" inscription, which typically stands for "Water, Oil, Gas". For most qualified plumbing specialists or plumbers, such inscription indicates that the valve can be safely installed in a gas, water or fuel oil plumbing network.
However, this inscription technically indicates that the valve can be submitted to a given level of internal pressure applied using water, gas or fuel oil. It does not refer, in any way, to the long-term behavior of a valve exposed to such media.
Information obtained from various plumbing parts manufacturers indicates that CSA (Canadian Standard Association) regulates the application of such inscription. Two other inscriptions are frequently engraved on such ball valves - namely "CGA 3.16" and "ASME B16.33". These inscriptions are referring to two standards which are exclusively applied to valves installed in gas plumbing networks. However, parts bearing such engravings are frequently found in various water plumbing networks.
CSA Standard B3.16 (2003) identifies various metals or materials that can be utilized for the manufacturing of ball valves. According to Standard B3.16, ball valves can notably be manufactured using cast iron, steel or bronze. In the case of bronze, the standard specifies that bronzemade valves must have a minimum copper content of 59%. However, it is important to note that the minimum copper content of many bronze alloys is about 88%. Moreover, such copper content is more typical of brass alloys which are mainly containing copper and zinc. This standard is thus not precise with regards to the material chemical composition that can be utilized to manufacture ball valves.
ASME Standard B16.33 (2002) is more precise as to the materials that can be utilized to manufacture valves. Like CSA, ASME authorizes the use of steel and cast iron to manufacture ball valves. However, ASME standard clearly states that ball valves can be manufactured with cast and forged brass alloys. With the exception of one alloy presented in this standard, the brass alloys authorized by ASME have a zinc content of more than 30%.
As for PEX plumbing fittings, such parts frequently bear inscriptions referring to ASTM Standard F1807. Manufacturing characteristics of such fittings are also described by CSA Standard B137. This standard applies, notably, to both commercial and residential water plumbing networks. To the contrary of CSA Standard 3.16, brass alloys for the manufacturing of PEX plumbing fittings are clearly specified in CSA Standard B137. According to CSA Standard B137, many brass alloys, with a zinc content of more than 30%, can be utilized to manufacture brass PEX plumbing fittings.
The standard also specifies that other alloys can be utilized, as long as parts made of such alloys have a corrosion resistance which complies with Article 6.1.1 of CSA Standard B125. This article is, however, referring to short-term corrosion resistance tests.
Our metallurgical investigation of valves as well as PEX plumbing fittings showed that many such parts were manufactured using a brass alloy with a zinc content of 30% or more. The ball valves were thus not complying with the material selection of CSA Standard 3.16 criteria. More precisely, the valves were made out of brass and not bronze, such as specified in the standard. However, the inscriptions "CGA 3.16", "WOG" as well as the "CSA" logo were engraved on those valves. The chemical composition of these valves was however complying with ASME Standard B16.33 criteria.
CSA and ASME standards criteria, more precisely those in relation with the ball valves chemical composition, are ambiguous. In fact, even if brass is not described and presented as an appropriate material for the manufacturing of ball valves, it is cited in CSA Standard 3.16 without introduction or precision as to the chemical composition that can be utilized for the manufacturing of brass-made parts. The ASME standard permits, on the contrary, the use of precisely defined brass alloys for the manufacturing of brass parts such
as ball valves. Documented ball valves were, however, bearing both CSA 3.16 and ASME B16.33 engravings.
As for the failures of PEX plumbing fittings as well as ball valves, the majority of metallurgical analysis revealed that the parts chemical composition played an important role in these failures. More precisely, high zinc brass (a zinc content of 30% or more) is not an alloy that is normally recommended for parts exposed to media such as potable water. As mentioned previously in this document, some standards recommend the use of high-zinc brass alloys. However, the use of such alloys for long-term service in applications such as potable water plumbing networks is generally not recommended in the scientific literature and by many known associations. Furthermore, CEP metallurgical analysis also revealed that the high-zinc level of such brass-made parts played a primordial role in their premature failure. Alloy with a zinc content of less than 15% are normally recommended for long-term service in water plumbing networks.
Finally, it is important to note that the good behavior of a brass part exposed to potable water is not necessarily guaranteed even if the part's characteristics comply with the appropriate CSA and ASME standards criteria. More precisely, a part's premature failure can happen even if it complies with all the criteria in the above-mentioned standards. It is thus not simple to design and build a reliable water plumbing network, when relying on criteria from such standards.