A Probe into Failure of Selected Plumbing Parts: Alloy Composition, Microstructural Condition and Aq

Journal of Metallurgical Engineering (ME) Volume 3 Issue 2, April 2014 doi: 10.14355/me.2014.0302.02

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A Probe into Failure of Selected Plumbing Parts: Alloy Composition, Microstructural Condition and Aqueous Exposure Iyiola O. OTUNNIYI*, Oluwayimika O. OLUOKUN Metallurgical and Materials Engineering, Federal University of Technology Akure, Nigeria *iootunniyi@futa.edu.ng; drolatunji@gmail.com Abstract A probe into the metallurgical integrity of selected plumbing parts was carried out for an informed evaluation of the failures observes in service. Faucets and sink drainer were focused on. Alloy compositions and microstructures were assessed, and test exposures to normal service conditions were simulated. Alloys were found with off-specification compositions, with residual stresses in the microstructures providing energy to initiate degradation early in service.

Hence, plumbing parts corrodes freely in ordinary neutral water, with metal overload in water. The materials choice and production design predisposes the units to short service life. Conformity to basic material and manufacturing standards is still lacking in some operations.

Keywords Plumbing Parts; Metallurgical Integrity; Materials Selection; Alloy Compositions; Residual Stress; Corrosion

Introduction Instances of very short service lives are very common experiences in using many consumer items in Nigeria in recent years. Plumbing fittings have been found to fail and had to be replaced within months. Service lives of electric bulbs have been found to average less than four weeks. Wall electrical outlets commonly heat up under household amperage, melt and burn the plastic housing. Electric stoves, water heaters, pressing iron, rechargeable lamps, ceiling lamp holders and IT products, often pack up in few months of use. The list is longer and there have been officially statements about the trend (Agboola, 2011). Since many of these items were imported into the country, such experiences can be expected in many parts of the globe.

For this work, plumbing parts that have been found to fail in service after remarkably short service lives were focused. Shower sprinklers and drainers (sieves in kitchen sink hole) produced to appear like stainless steel have been found to rust to dirty brown within

less than 24 weeks of fitting. Drainers rust and crumble into pipe work. Taps not used for a few days have been found to first dispense a burst of brownish globule before clear flow. Such tap heads often cease to hold flow after about four months. The tap continues to drip and must be replaced. Whereas, a plumbing part is expected to be noncorrosive, and durable enough to equal or exceed the expected life of the building in which it is installed (Encyclopedia B., 2010) When a consumer item fails after a short service life, it can be a case of abuse by the user, or a single defective product out of many other good ones. When this observation is in all instances of use, the logical thinking is that these items are not made to safe and durable standards from source. No position will be final without an empirical basis for its conclusion.

Selected plumbing parts were therefore investigated and reported herein. The alloy compositions were determined and compared to standard material specifications for such units (BSI, 1991; CDA, 1991; Ramesh, 2011; Malekith, 2013), and the microstructural conditions of the alloys as-used were studied. Test exposure to the service condition (neutral water) was simulated. It was also found necessary to assess possible metal load of water dispensed by such faucets.

The results were discussed from different viewpoints.

Methodology For a documentary, visual inspection of striking instances of faucets and drainer failure, as found in service were carried out. From a survey of the varieties of these items available in the plumbing stores, four most common faucets found in the shops and a drainer, were obtained. For reference, Table 1 gives designations and summary description of the items. The samples were dissembled, scratched, sawn, and cut apart, as necessary, to visually assess surface and bulk body material make up.

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Journal of Metallurgical Engineering (ME) Volume 3 Issue 2, April 2014

Spark spectrometric analysis of separate alloys making up the units was done. For the faucets, the alloys used in the central control rods in F1 – F3, being the major moving part, and the housing alloys, being the bulk material, were analyzed. Since mechanical and heat treatments affect microstructural condition, which in turn affects service performance, metallographic samples of the alloys analyzed were obtained. Optical microstructures of the alloys were obtained.

Microstructure and compositional analysis were similarly done for the drainer.

TABLE 1 DESIGNATION AND DESCRIPTION OF FOUR COMMON FAUCETS AND THE DRAINER STUDIED

Designation

F1

F2

Features and description A circular indentation around the valve control rod of the faucet reads ENGLAND EURO UK. On the faucet housing (the gland), on one side, letters SF and on the other side ‘BS 10102’ and ‘½’ were boldly embossed as-cast. Uses screw control mechanism.

Similar to F1 expect with no indentation or embossed, and the stem appears to be of steel luster.

water above another set of samples using a small impeller attached to the thin shaft of a small DC motor.

The motor was powered for four hours in a day; since the tap in a typical household will not dispense water round the clock, while in a typical public utility the tap can be expected to run cumulatively for about four hours a day. Measurement of any changes in the samples mass was done weekly for six weeks, with the water above the samples replaced with every measurement.

From the corrosion test (results below), possible level of pollution of water dispensed by such faucets was also assessed. Sample was taken from the water in which the component alloys were placed, and analyzed for metal load using atomic absorption spectroscopy (Haswell, 1991; Welz, 1999). With the respective lamps, the water sample was analyzed for iron, copper, sodium, lead, potassium, and zinc.

F3

Similar to F1 in stem, and embossed letters but with different structural design.

Results and Discussion

F4

Stainless steel appearance; flow control mechanism by aperture opening and closing in 90O turn.

Exhibits

D

A sample drainer; the sieve covering drain hole in a kitchen sink.

From the visual inspections, Figure 1 presents exhibits of sample faucets as found in service. Corrosion stains and rusts to different extents on the stem (the central control rod) and towards the supporting threaded nut can be seen on the faucets. For plumbing fittings to corrode visibly in this manner in service, the material selection and the production design are strongly suspects. The faucets shown in Figure 1 are of the type designated as F1.

For a quantitative check on the performance in the service environment, test exposure to the service medium was simulated. The disassembled components were left undisturbed to simulate the static condition of a tap that is not dispensing water. Since in service, water is not static but actually runs in the tap, the dynamic flow service condition was simulated by stirring the

FIGURE 1 INSTANCES OF TAP1 AS FOUND IN SERVICE – SHOWING DETERIORATION LEVELS AND EMBOSSED PRODUCTION STAMP SHOWING SUPPOSED STANDARD SPECIFICATION KEPT.

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(c)

(a)

(b) FIGURE 2 TAP SAMPLES AS OBTAINED FROM THE PLUMBING SHOP

Figures 2a – c show new samples of F2, F3 and F4 as obtained from the plumbing shop. Examining the samples, the stem in F2 shows steely luster, and it is presumably machined from rolled bars. The main faucet body is apparently made of brass, with as-cast surface texture. It is notable that the stem and the valve housing are not of the same alloy. This portends a dissimilar metal violation for a unit that will be susceptible to wet aqueous exposure in service. In F1 (new one is not shown), the stem has the same brass coloration as the housing. On this basis, F1 in new form appears to be of better material selection in its design and production, compared to F2, since the possibility of dissimilar metal galvanic effect appears to be removed. However, while holding F1 around in the course of observation, the stem started showing discoloration (due to inadvertent rubbing by fingers), exposing portions with steel luster. Portions showing steel and brass coloration like this were found in service also (Figure 1). The stem obviously has a thin (possibly submicron) coating, with poor adhesion. In F3 the stem is also coated as in F1, but the coating did not rub off so readily.

F4 is a different design, with covered stem and the housing of stainless steel luster. The housing surface when scratched with a pin indented deep and softly, unlike stainless steel but rather more like an organic coating. With a hand saw and file, a thin undercoat showing reddish brown on a bulk body of dull white luster was revealed. The bulk material of the housing thus appears to be of steel, with a faint first coat of copper, and a final tenacious surface coat that can be organic.

F1, F2 and F3 are similar in working mechanism: the

threaded stem is turned downward to block flow by closing against a polymeric o-ring. The valves will continue to block flow as long as the polymeric disc remains resilient and the stem maintain its length. In F4, a turn through 90O allows or stops flow when holes in two polymeric components align or not, respectively. One of the polymeric components sits on a stem that appears as cast brass. The stem turns the polymeric piece in and out of alignment with the other piece that is fixed in the flow channel. The unit will continue to regulate flow effectively as long as the aligning polymeric components do not degrade but maintain tight tolerance. Based on visual inspection, production of F4 appears of a best material selection and design.

Figure 3 shows a sample drainer in service that has corroded and crumbled, and a new sample. The new sieve appears of stainless steel, but this surely cannot be if the new is of the same material as the one observed in service, which corroded so badly that part of it crumbled into the pipe works. The fitting bolt gave way and can no longer hold it in place. The results of analysis are presented following.

FIGURE 3 DRAINER SIEVE AS FOUND IN SERVICE INSIDE A DRAINER AND A NEW ONE.

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Journal of Metallurgical Engineering (ME) Volume 3 Issue 2, April 2014

Compositions of Component Alloys Table 2 shows the elemental compositions of different alloys in the study. Columns R1 to R3, gives the compositions for the control rods in F1, F2 and F3 respectively, while H1 to H4 are for the housing alloys of F1 to F4. Column D is for the drainer, ST is for the generic BS 1400 brass alloy recommended for fresh water faucets, and column SD is for AISI-SAE Grade 304 stainless steel recommended of the drainers (CDA, 1991; MatWeb, 2013). Among many equivalents, specifications BS 5154: 1991, BS 12288: 2010, BS EN 12163: 2011, BS EN 1982: 2008 cover specific brass alloys for components of fresh water valves, while BS EN 10088-1: 2005 number 1.4301 or 1.4401 covers stainless steels for screens (BSI, 1991; ASD, 2012).

According to the compositions in Table 2, the housings of F1, F2 and F3 were confirmed to be brass alloys, while that of F4 is a zinc-aluminum alloy. The central control rods in F1, F2, and F3 were found to be of medium to low carbon steels (MatWeb, 2013). The drainer was also of low carbon steel and not stainless steel according to the standard in column SD. Compared to the standard specifications, there are random elements in the alloys compositions. This can be traced to recycling charge. More than half of metal productions in the world are now sustained by scrap

recycling (Papp, 2001). Production of finished parts using only ingots smelted from primary ores is increasingly rare. Different copper alloys in the BS2870/5, BS3072/6, BS1400 specifications (the PB10x, CN10x, AB10x, CA10x, ABx series) contains definite amounts of Al, Si, Mn, Fe, Pb (Higgins, 1999; Callister, 2001). There are precipitation hardened copper alloys containing Cr and Be. For steels and irons, the existing alloys are more (MatWeb, 2013). Such assorted alloys get into scrap feed in recycling, and the charge calculation settles for the closest optimum. If a heat produces off-specification composition, the product becomes new scrap (Papp, 2001). If an operation weighs economics too high, compositions such as obtained herein will be the result.

For the control rods and the drainer, the compositions cannot be classed as stainless steel based on the Ni and Cr, nor as Mn-Si steel; all the elements were not up to requisite levels (Callister, 2001; MatWeb, 2013). Trace Al and Cu were also detected. Based on the carbon levels, the alloys can be said to have been produced from assorted ferrous scraps charge, roughly targeted toward mild steel but turned out off-specification.

Compositions that are roughly mild steel are inadequate for plumbing applications for which they have been employed (Blower, 2006; Ramesh, 2011; Malekith, 2013).

TABLE 2 ELEMENTAL COMPOSITION (%) OF ALLOYS USED IN THE DRAINER (D), THE CONTROL RODS (R) AND HOUSING (H) OF THE SAMPLE FAUCETS, AND THE STANDARD SPECIFICATIONS OF SUCH PARTS.

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R1

R2

R3

H1

H2

H3

H4

ST

D

SD

Al

0.023

0.149

0.003

0.0088

0.245

0.087

83.3

0.1-0.8

0.031

0.100

As

0.034

0.032

0.016

0.014

0.014

--

C

0.193

0.244

0.195

--

--

--

--

0.142

0.080

Cr

0.532

0.313

0.0042

0.0068

0.02

0.069

0.070

0.084

20.000

Cu

0.037

0.04

0.0033

58.2

67.5

54.2

1.86

58-63

0.081

Fe

97.7

97.35

99.3

0.74

0.95

0.7

0.5

0.7

99.2

68.995

Mn

0.79

1.02

0.369

0.009

0.005

0.003

1.18

0.5

0.108

2.000

Ni

0.009

0.015

0.021

0.306

0.281

0.281

--

1

0.053

8.000

P

0.036

0.037

0.047

0.0079

0.005

0.005

--

0.02

0.045

0.045

Pb

0.003

0.001

0.002

2.61

5.63

6.22

0.05

0.5 - 2.5

S

0.024

0.03

0.020

0.0061

0.011

0.007

--

--

0.048

0.750

Si

0.58

0.71

0.021

0.013

0.066

0.14

1.3

0.05

0.188

0.030

Sn

0.026

0.027

0.0012

0.81

2.44

1.6

0.146

1

0.0043

Zn

--

--

0.013

37.17

22.68

36.65

11.40

30.43 – 38.13

0.01

--

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For the housing alloys, reference to column ST in Table 2, a plumbing faucet will be made of brass alloy. All the components of the unit – the housing, the turning knob, the control rod – are mandated to be of the same brass alloy (CDA, 1991). The brass alloys used in the housings deviated with respect to different elements.

The Pb levels in H1 (F1 housing) is close enough to be acceptable, while that in F2 and F3 exceeded this level.

Lead level of 2.5 maximum is the standard, while F2 and F3 contained 5.63% and 6.22%. Pb is notably carcinogenic for humans and strict restrictions apply to the presence and use of this element according to the RoHS directive (Directive, 2003). Permitted levels may therefore not be exceeded. Chromium is another element not expected but found in trace proportion. It may not be a threat in this context, but can rather improve corrosion resistance of the alloy. More so that these housings did not fail in service instances inspected, or show any dissolution during the corrosion testing (see below), the brass alloys used in the manufacture of the faucet heads can be considered

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acceptable.

The bulk body alloy used in F4 housing found to be of aluminum alloy is a good alternative to the brass alloys. The composition shows an Al-Zn alloy that can come under the BS 1475:7000 series. Aluminum is known for its tenacious thin surface oxide which makes aluminum alloys naturally corrosion resistant (Snodgrass, 2003). The surface of this faucet was also treated to a tenacious coating, and the material can be considered acceptable.

Microstructures of Component Alloys The housings of the various faucets generally show different as cast microstructures. Since the housings actually did not give any problem in service or in the corrosion test, the micrographs are inconsequential in further analysis of the performance problem. Figures 4a and b, micrographs obtained for H1 and H3, were therefore shown only as representative micrographs of the brass housings.

FIGURE 4 OPTICAL MICROGRAPH OF THE BRASS HOUSING OF (A: LEFT) TAP1, SHOWING A GRANULAR AS-CAST α + β’ STRUCTURE (EXPECTED AT 37 % Zn, X 400), AND (B: RIGHT) H3, SHOWING A PREDOMINANTLY α-BRASS MATRIX (AT 22 % Zn, X 200) WITH EQUIAXED AS CAST STRUCTURE.

FIGURE 5 OPTICAL MICROGRAPHS OF THE VALVE CONTROL RODS OF (A: LEFT) TAP1 SHOWING AS-ROLLED DIRECTIONAL GRAIN (X 400) AND (B: RIGHT) TAP2 SHOWING RECRYSTALLISED GRAINS POSSIBLY FROM FULL ANNEAL (X 400).

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FIGURE 6 OPTICAL MICROGRAPHS OF (A: LEFT) THE VALVE CONTROL ROD OF TAP3 SHOWING THE AS ROLLED STRUCTURE LARGELY RELIEVED, THOUGH LITTLE FLOW IS STILL RESIDUAL (X 400), AND (B: RIGHT) THE DRAINER SIEVE WITH CLEARLY FLOWED PEARLITE MORPHOLOGY IN A FERRITE MAIN MATRIX (X 400).

Considering the microstructure from R1 (Table 2) shown in Figure 5(a), it can be inferred that the stem was machined to size from the rod in as-rolled condition.

The microstructure shows grains with preferred orientation ascribable to the rolling direction (Tatsuya and Kenji, 2010). In this state, this rod was used asworked, and with the strain energy not relieved. It was therefore more corrosion active than if some stress relief annealing had been performed on it (Van Boven et al., 2007). Here is another insight into why the stem was, as it were, dissolving in ordinary water at room temperature. The micrograph of R2 shows rather recrystallised grains, possibly from full anneal of the as-rolled rod used in the production of the stem. For F3, as Figure 6 indicates, the stem can be said to have been turned from an alloy that was worked and then treated only to stress relief anneal. From Figure 6b, the drainer is in a slightly worked state, with the residual stress unrelieved. This could have been from the little deformation during press forming. A fully relieved structure is a better condition for reducing corrosivity (Higgins, 1999). In the production design of F1, F3 and the drainer, this fact was disregarded. Production design in F2 is mindful of this, but the bulk alloy is essentially not corrosion resistant.

The highpoint thus far is that the central valve control rod in F1, F2 and F3 were of alloys that are clearly unsuitable, of mild and low carbon steels and not brasses. The drainer alloy was also not of stainless steel according to specification. These alloys are inappropriate and are not expected in applications for aqueous exposure. Some are also in worked states. To have used such alloys for these applications in the first place is bad enough; to keep the alloys in a worked state, with residual energy in the microstructure, is worse. This predisposed the items to such poor performance as found in service. The results of the test

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exposures track the degradation in service with time.

Corrosion Behavior of the Faucet and the Drainer Alloys Of the various components of the faucets exposed to static and flowing water, all the component parts of F4 did not show any degradation. No noticeable corrosion was observable. The mass measurements remained constant. In the other faucets, the central valve control rod corroded glaringly, turning rusty brown on the surface, while the water also turned brownish. The mass measurements showed mass loss in the rods. Figure 7 shows the cumulative mass loss in the different control rods under the two conditions over the 42 days of exposure. From the figure, the material used for the control rods in F1, F2 and F3 cannot survive exposure to ordinary water at room temperature. Even under static exposure, corrosion of the rods was progressing. Under the dynamic condition, the rate increased, indicating erosioncorrosion (Rabald, 1991). These central control rods are the very component of the valve that blocks the flow.

This implies that, in the locked condition, the faucets will continue to degrade. Related to service performance, the corrosion observed under static condition accounts for the first globule of brownish water that burst from these faucets after some days of inactivity.

On a closer study of the data in Figure 7, in the first week of exposure, the mass loss rate was relatively highest for control rod of F3. This latter slowed down, relatively, before the corrosion continued steadily. This can be a passivation - transpassive behavior (Kruger, 2003), but the imperfect coating on the surface of the rod could be more responsible. With imperfect coating, coating breakdown, surface corrosion, local galvanic action with the substrate, exfoliation, peeling, and blistering to different extents can occur (Roberge, 1999).

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Mass loss rate can therefore reduce after the coating is fully consumed, and some modes of corrosion cease.

However, the corrosion did not passivate. There is also such coating on F1. Corrosion commences right from the very first week of exposures and continued steadily. Cummulatively, F3 gave lower mass loss, and F1 the higher. In both cases, the manufacturers would know that the coatings do not offer short or long term protection to the substrate. These coatings must have been for sale cosmetics only. Overall, the control rod of F2 recorded the highest mass loss over the time interval, while F1 and F3 were in the trail. All the dissolution is continuous, and will not passivate. The

faucets will cease to control flow after short service life.

The drainer also was found to corrode under water.

Figure 8 shows the drainer response over the period under dynamic exposure. It was noted that the response was initially slow. The coating first tended to resist degradation, but later tarnished and gradually gave way. The rate of corrosion then aggravated. As the sample corrodes in this manner under neutral water, more profuse corrosion till failure as found in service (Figure 3), can be expected. When exposed to the real kitchen waste water streams, with pH shocks above and below 7, depending on what is cooking, and thermal fluctuations, the product is surely a failure.

R1-Static R1-Dynamic R2-Static R2-Dynamic R3-Static R3-Dynamic

12

Cumulative mass loss per unit area (mg/cm2)

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10 8 6 4 2

Time (days)

0 0

10

20

30

40

Cummulative mass loss per unit area (mg/cm2)

FIGURE 7 CUMULATIVE MASS LOSS PER UNIT AREA UNDER STATIC AND DYNAMIC EXPOSURES OF CONTROL RODS IN F1, F2 AND F3, DENOTED AS R1, R2 AND R3 RESPECTIVELY.

6 5 4 3 2 1 0 0

10

20

30

Time (days)

40

FIGURE 8 CUMULATIVE MASS LOSS PER UNIT AREA OVER TIME OF EXPOSURE OF THE DRAINER SIEVE TO ORDINARY WATER UNDER DYNAMIC CONDITION, WITH VIEWS OF THE CORRODED TEST SAMPLE INSET.

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Obviously, the alloys used for the different components are unsuitable for these applications, virtually dissolving under exposure to ordinary water, only with the exception components of F4. These types of products will only put the consumer in a vicious cycle of replacing the plumbing fittings forever.

Metal Load in Water With the dissolution of the faucet control rods in presence of ordinary water, expect for F4, metal load in water dispensed by such faucets raises concern. The AAS analysis shows various metallic elements in the water sample (Table 3). The allowable levels for safe drinking water for these elements by some standard bodies (United Nations WHO, USA’s EPA and Nigeria’s NSDWR) are also shown in the table (NIS 2007; EPA, 2010; WHO, 2011). It may be needed to restate that the water sample analysed was taken above the corroding control rods, and the analysis is indicative of possible contaminations that this rods can contribute to water dispensed by the faucets. It does not account for many other possible source of contamination of pipe borne water. It may be needed also to state that the water has become faint brown due to the corrosion dissolution. This analysis may therefore represent the first brownish globule observed in service when the faucets have not been used for some days. Clear flow normally follows after such first brownish burst, although how clean such clear flow can be is clearly debatable.

TABLE 3 METAL LOAD IN WATER SAMPLE FROM CORRODED PARTS

Elements Chromium (Cr) Copper (Cu) Iron (Fe) Lead (Pb) Manganese(Mn) Nickel (Ni) Zinc (Zn)

Tested Water Sample (mg/L) 0.074 0.186 130.8 1.039 0.027 28.833

NSDWR WHO EPA (mg/L) (mg/L) (mg/L) 0.05 0.05 0.1 1 2 1.3 0.3 -0.3 0.01 0.01 0 0.2 -0.05 -0.07 -3 3 5

Definite information from this analysis is that six metallic elements can leach from these control rods into household cup of drinking water. The list includes chromium, known to serve no biological function in the body, but rather a cumulative poison (Chowdury and Chanda, 1987. Chromium can also exist in the hexavalent state, which is particularly listed as hazardous. Elements such as iron and zinc that are dietary elements can be loaded beyond limits from these units, as the data show. Iron overload disturbs pH balance, predisposing patient to permanent coma in the worst case. Human exposure to metals from tap

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water is known for a long time, with lead plumbing being notorious. From the data herein, excessive dosage of many other metals may soon add to the global health concerns from different vulnerable regions where these substandard parts still enjoy sales.

Conclusion Study of alloys used in production of sample plumbing parts – faucets and drainer – shows cases of bad material selection and production design. The composition analyses show the alloys as off specification compositions, but close to mild steel. The alloys are actually from assorted scraps charged not to a strict composition target. The microstructures show that some of the alloys are in stressed states, providing internal energy to hasten degradation. There are dissimilar metal coupling too. Active surface corrosion of the critical moving parts triggers on exposure to service condition (drinking water). Coatings were only for sale cosmetics. Corrosion was sustained in erosioncorrosion mode by fluid current so that passivation will not occur. The short service life as found in service is expected. Metal load in the water dispensed from such taps can be far above safe portable water threshold. The products were produced to a gross substandard. It is an indication that conformity to basic materials and manufacturing standards is still lacking in some operations.

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Iyiola Olatunji OTUNNIYI is a Metallurgical Engineering academic.

He studied at Obafemi Awolowo University Ile-Ife, Nigeria and University of Pretoria, South Africa.

He holds a PhD degree and has more than ten years of teaching and research experiences in Universities and Institutes.

Oluwayimika O OLUOKUN is a notably bright upcoming Metallurgical Engineer. He studied at Federal University of Technology, Akure and took interest in materials quality and integrity in service, metallurgical plant and process design.

Subramanian, T.K.S. and Venkata R. B. “Impact of household

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