BlackPowder.pdf

Black Powder in Sales GasTransmission Pipelines

2 SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2007

Dr. Abdelmounam M. Sherik

Abdelmounam M. Sherik works for Saudi Aramco’sResearch and Development Center in the Upstream R&DProgram as project leader, Black Powder Management.Prior to joining Saudi Aramco, Dr. Sherik worked inCanada for 15 years where he held several researchpositions in university, governmental and industrialresearch centers. Abdelmounam holds a B.Sc. in MaterialsScience and Engineering from Tripoli University, Libyaand a M.Sc. and Ph.D. in Materials and MetallurgicalEngineering from Queen’s University, Canada.

In addition to his leadership of the black powdermanagement project, Abdelmounam’s research interestsinclude nano-structured coatings and processing-microstructure-properties-performance relationships inmaterials. Dr. Sherik has authored and co-authored morethan 40 publications in the field of nano-structuredcoatings. His Ph.D. work on nano-coatings has led toseveral patents and the startup of a spin-off company inCanada, to further develop and commercialize the newlydeveloped nanotechnology-enhanced coatings.Abdelmounam is currently leading a technology project toimplement nano-coating in the repair of heat exchangertubes in Hawiya Gas plant, as well as exploring potentialapplications of these coatings throughout Saudi Aramcofacilities. He is an active member of the NationalAssociation of Corrosion Engineers (NACE).

SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2007 3

ABSTRACT

While it has long been recognized that black powder canhave a serious impact on customer complaints and pipelineoperations, namely instrument scraping delays and reducedin-line inspection accuracy, as well as control valve and pipeerosion (with potential safety impact), there has been littleunderstanding of the composition, source and formationmechanisms of black powder in Sales Gas transmissionpipelines. Without such fundamental knowledge of sourceand formation mechanisms for black powder, the longstanding question, within Saudi Aramco, of whether blackpowder is regenerative (i.e., the source is corrosion, morespecifically as a result of hydrotesting operations) or non-regenerative (i.e., the source is degradation of steel millscale) cannot be resolved. The resolution to this question isnot an academic pursuit, but has significant practicalimplications on the selection of appropriate black powdermanagement methods.

The results of this work showed that none of the analyzedblack powder samples showed hematite-Fe2O3 or wuestite-FeO that are typical iron oxide phases found in mill scale.Our findings have shown that black powder in Sales Gastransmission pipelines is mainly composed of ironhydroxides (goethite-FeOOH and lepidocrocite-FeOOH) andan iron oxide (magnetite-Fe3O4). Less than 30% of thesesamples showed small amounts of siderite-FeCO3 in additionto the iron hydroxides and iron oxide. These compoundsindicate that internal corrosion of the internal walls of theSales Gas lines is the source for black powder. Finally, it wasfound that laboratory simulated hydrotesting did not lead tothe formation of iron oxide-based black powder.

INTRODUCTION

Black powder is a worldwide phenomenon experienced bymost, if not all, gas pipeline operators1-5. Saudi Aramco’sapproach to managing black powder is unique andproactive to the rest of the industry in that it is pursing theevaluation and implementation of several removal methodssuch as mechanical and chemical cleaning; installation offilters and inertial separators concurrently with developing abasic understanding of black powder composition, sourceand formation mechanisms in order to prevent it. Todevelop this basic understanding, degradation of mill scaleand internal corrosion of pipelines were investigated aspossible sources for black powder formation. Laboratorysimulated hydrotesting was also conducted on steel samplesto study the effects of hydrotest parameters such ashydrotest duration, water quality, oxygen scavenger anddrying conditions on black powder formation. X-raydiffraction (XRD), X-ray florescence (XRF), scanning

electron microscopy (SEM) and microhardness techniquesas well as several bacterial analysis methods were used toanalyze a large number of black powder samples collectedfrom the field. Similarly the surface deposits, formed onsteel samples subjected to simulated laboratoryhydrotesting, were analyzed using XRD and bacterialanalyses.

This paper is divided into two main parts. In the firstpart a summary of reviewed literature on black powder,internal corrosion of pipelines and steel mill scale ispresented. The second part of this paper briefly describesthe experimental program and analysis of results carried outto determine composition, source and formationmechanisms of black powder in Sales Gas pipelines.

REVIEW OF PUBLISHED LITERATURE

Black Powder

In the gas industry, the term “black powder” is a color-descriptive term loosely used to describe a blackish materialthat collects in gas pipelines leading to erosion failures ofvalves, Fig. 1, lower efficiency for compressors, clogging ofinstrumentation and valves and customer complaints1-5.Black powder can be found in several forms such as “wet”and have a tar-like appearance, or “dry” and it can be avery fine powder as shown in Fig. 2. Black powder wasreported in recently commissioned as well as older SalesGas transmission pipelines. As used in the surveyedliterature, “black powder” means various forms of ironsulfide, iron oxide and iron carbonate, mechanically mixedor chemically combined with any number of contaminatessuch as salts, sand, liquid hydrocarbons, and metal debris.Different gas pipeline operators report differentcompositions for the black powder removed from their

Fig. 1. Shows dry and fine black powder collected at the scraper door receiverof a Sales Gas pipeline.


pipelines. For example, whereas some literature reportsblack powder as being predominately iron sulfides1-3,others report the complete absence of iron sulfides but thepresence of iron oxides such as Fe3O4 and FeOOH4, 6,while others report a combination of all of these products(iron sulfides, iron carbonates and iron oxides)5. Theseproducts have one common source, which is that they areformed inside natural gas pipelines as a result of corrosionof the internal walls of the pipeline1-6, more specifically, byreactions of iron (Fe) present in ferrous pipeline steel withcondensed moisture containing oxygen (O2), hydrogensulfide (H2S) and carbon dioxide (CO2). The productsproduced by reaction of these species with pipeline steelhave common characteristics: They are all relatively high inspecific gravity (sp. gr. 4 to 5.1), abrasive and are typicallydifficult to remove in cleaning operations5. Case historiesshowed that large quantities of black powder can begenerated inside pipelines. For example, 8,000 lbs of blackpowder were removed from a 16” x 80 km gas pipeline inHouston and 500 kg of black powder were removed from a36” Greek Sales Gas transmission pipeline extending for adistance of 12 km4.

Internal Corrosion of Sales Gas TransmissionPipelines

Internal corrosion in “dry” gas pipelines is often overlookeddue to an underestimation of the corrosion risk due to theperceived absence of condensed water in the line1, 7. Undernormal conditions, gas pipelines are under minimalcorrosion risk; however, it is not possible to completelyeliminate water from pipelines7. Water vapor canpotentially condense on the inner walls of the pipeline dueto high dew points. Water vapor can also enter the pipelinethrough periodic upsets that cause water carry-over into theline. This water coupled with corrosive species such as CO2,

H2S and O2, in small amounts, as low as ppm levels, canresult in unexpected internal corrosion with the formationof corrosion products namely FeCO3, FeS and ironoxides/hydroxides, respectively1, 5. It should be noted thatthese components are benign in dry gas but form weakacids that can cause significant corrosion in the presence ofcondensed water1.

Carbon dioxide is a naturally occurring constituent ofnatural gas; this is in contrast to oxygen which can ingressthrough leaks at low-pressure points throughout thepipeline systems1. Oxygen ingress in gas lines can causesignificant corrosion in small concentrations and evencombustion in larger amounts8, 9. A 1988 survey of 44natural gas transmission pipeline companies in NorthAmerica indicated that their gas quality specificationsallowed maximum O2 concentrations ranging from 0.01mol% to 0.1 mol% with typical value of 0.02% mol8, 9. Ithas been shown that oxygen content of approximately 0.01mol% has little effect on steel corrosion in the presence ofstagnant water inside Sales Gas transmission pipelines,while 0.1 mol% produces fairly high corrosion rates. As ageneral rule of thumb, it has been recommended thattransmission pipelines should consider limiting maximumoxygen concentrations to 10 ppmv (0.01 mol%)8, 9.Hydrogen sulfide can also be a naturally occurringconstituent of natural gas or alternatively, produced bysulfate reducing bacteria (SRBs)1. These anaerobic bacteriause the reduction of sulfate as a source of energy andoxygen, in accordance with reactions such as1, 2:

2H+ + SO4-2 + CH4 → H2S + CO2 + 2H2O (1)

It is important to note that condensed water is a perquisitefor these bacteria to thrive and multiply and as such,reaction1 cannot occur in the absence of water. Because ofthis, typical Sales Gas standards specify a maximum moisturecontent limit of 7 lbs water/mmscf (0.112 mg/l)1.

Corrosion due to H2S, CO2 and O2 in Sales Gaspipelines has well established mechanisms. Following aresimplified electrochemical reactions that describe thesecorrosion processes and their respective corrosion products.It is important to note that in all of these electrochemicalreactions, condensed water is a necessary condition forthese reactions to proceed.

1. Siderite-FeCO3 Formation Due to CO2 Corrosion

The source of siderite-FeCO3 corrosion product is thechemical reaction of dissolved CO2 in condensed waterproducing carbonic acid which in turn reacts directly withsteel to produce FeCO3, in accordance with thesereactions10:

Fig. 2. Shows erosion damage, due to black powder, to the casing of pipelinecontrol valves.


H2O (condensed water) + CO2 (in gas) →H2CO3 (carbonic acid) (2)

H2CO3 + Fe (pipeline steel) → FeCO3 + H2 (3)

2. Iron Sulfides Formation Due to H2S Corrosion

Iron sulfides (FeS) corrosion products are usually formedfrom H2S, naturally occurring in natural gas or producedby SRB, reacting directly with the steel wall of the pipelineas per the following reactions1, 2:

H2O (condensed water) + H2S (in gas) →H3O+ + HS- (4)

HS- + Fe (pipeline steel) → FeS + H2 (5)

3. Iron Oxides Formation Due to Oxidation

In cyclical wet-dry low dissolved oxygen environments, ironoxides are usually formed by the direct oxidation ofpipeline steel walls, in accordance with the followingreactions10:

2Fe + H2O (condensed water) + 3/2 O2 →

2 α β or γ -FeO(OH) (6)

In waters containing low concentrations of dissolvedoxygen as is the case in Sales Gas environment, the γ -FeO(OH) is unstable and will quickly transform tomagnetite-Fe3O4 and water by the following reaction10:

8 γ -FeO(OH) + Fe → 3Fe3O4 +4H2O (condensed water) (7)

But if the water is nearly saturated with dissolvedoxygen, then hematite (Fe2O3) is often present10.

Alternatively, iron oxides may be formed due to micro -biologically induced corrosion (MIC) resulting from acidproducing bacteria (APB) or iron oxidizing bacteria (IOB)1, 2. Once again, condensed water is a prerequisite forthese bacteria to thrive and multiply and as such, MICcannot occur in the absence of water.

Mill Scale

Mill scale is formed on steel through chemical oxidation ofiron with oxygen at high temperatures during steelprocessing operations11. Mill scale can be found as asurface layer on all new hot rolled steel plates similar tothose from which pipelines are made. Mill scale is a hard,brittle scale of several distinct layers of iron oxides formedduring the high temperature processing of steel11. It is

comprised of three oxides of iron that differ in theirproportion of oxygen in a discrete layered structure:Wuestite-FeO is the innermost layer (closest to steel),hematite-Fe2O3 is the outermost oxide in the scale layer,and magnetite-Fe3O4 is the intermediate layer as can beseen in Fig. 311. Wuestite, the layer next to the steel surfaceconstitutes about 85% of the scale thickness, the magnetite10% to 15% and hematite 0.5% to 2%. Mill scalethickness is dependent on steel processing operations and istypically in the range of 6 μm to 12 μm12.

Mill scale, usually bluish-grayish in color, cracks andfissures readily and is permeable to both air and moisture.Since mill scale is cathodic to bare steel, when corrosiveenvironments reach the mill scale-bare steel interface,corrosion (rust) occurs. Corrosion products (Fe2O3 orFeOOH) are more voluminous than the bare steel. It isestimated that these corrosion products occupyapproximately two times the volume of the steel from whichthey have originated. Due to this volume change, pressure iscreated at the mill scale-bare steel interface which in timeleads to removal (sloughing off) of the mill scale.

METHODOLOGY OF INVESTIGATION

To achieve the objective of this study a systematic andcomprehensive approach taking into account the followingtasks was undertaken:

1. Characterization of black powder.2. Characterization of steel mill scale. 3. Analysis of Sales Gas from corrosion point of view.4. Investigation of the effects of hydrotesting parameters

on black powder formation.5. Thermodynamic analysis of formation of black

powder in Sales Gas pipelines.

Fig. 3. Shows typical layered structure of mill scale exhibiting the various ironoxide phases (adopted from Ref. 12).

EXPERIMENTAL PROGRAM

Black Powder Sampling and Characterization

A total of 17 black powder samples were collected from 17different locations including scraper receiving traps andpump stations. The pipelines from which these sampleswere collected ranged in their service life from 3 to 30years. To avoid any possible oxidation of the black powdersamples, it was ensured that pipeline equipment (e.g.,scraper doors) was not opened until collection staff was on-site. All black powder samples were immediately collectedin silicon oil and under inert gas (Argon). X-ray diffraction,XRF and SEM techniques were performed to identify phasecomposition and physical appearance of black powder.Several bacterial analysis methods were performed in-houseand at the Gas Technology Institute (GTI)-USA on anumber of black powder samples.

Mill Scale Characterization

Typical pipeline steel plate was cut into appropriate sizesfor subsequent surface and cross sectional characterization.X-ray diffraction was used to characterize the chemicalcomposition of the mill scale present on the as-received steelplates. Optical stereomicroscopy was also used tocharacterize the mill scale surface in the as-receivedcondition. Metallographic cross sections of the steel sampleswere prepared for subsequent thickness determination usingthe SEM technique.

Analysis of Sales Gas

Sales Gas sampled from seven different sampling points wascollected and analyzed for H2S, CO2 and O2. Moisturecontent of the gas was also measured using indirect anddirect methods. The latter is done by using the methanolscrubbing method and the former by using the panametericdew point analyzer method. All gas samples were collectedand analyzed by the appropriate area laboratories.

Laboratory Simulated Hydrotesting

Laboratory simulated hydrotesting was conducted onpipeline steel samples with and without mill scale to studythe effects of hydrotest parameters, such as hydrotestduration, water quality, oxygen scavenger and dryingconditions on the formation of various iron oxides. Opticalstereomicroscopy coupled with XRD analyses were used tostudy the surfaces of the steel samples before and afterhydrotest procedures. Bacterial analyses were alsoconducted on the deposits formed on the surfaces of thesteel samples.

Autoclaves were used to conduct the simulated hydroteston pipeline steel samples with and without mill scale. The

test matrix consisted of eight exposures of the pipeline platesteel samples in conditions that are representative of fieldhydrostatic testing. Table 1 shows the test matrix for a oneweek test duration. A similar test matrix was utilized for afour week duration testing. Three replicate samples weretested at each condition. Only one side of each sample, withan exposed surface area of 25 cm2, was left exposed to thehydrotest water and the remaining sample sides werecompletely covered using epoxy coating. For sampleswithout mill scale, the mill scale was completely removedby immersion in 50% concentrated HCl acid. Immediately,after removal of mill scale, these samples were cleaned withdistilled water and immersed in 0.1N NaOH solution forseveral seconds.

The prepared steel samples were then immersed in

Table 1. The experimental test matrix using 40,000 total desolved solids (TDS)water was used in the laboratory simulated hydrotesting for a one weekduration. A similar matrix was developed for a four week duration test

Table 2. Composition and properties of Sales Gas used in the current work


TestSet

OxygenScavenger

MillScale

Surface DryingConditions

Repli-cations

1 Yes Yes Fast drying 3

2 Yes Yes Slow drying 3

3 Yes No Fast drying 3

4 Yes No Slow drying 3

5 No No Slow drying 3

6 No No Fast drying 3

7 No Yes Slow drying 3

8 No Yes Fast drying 3

Composition andProperties of Sales Gas

Levels

H2S 2.0 ppm and 6.0 ppm

CO20.1 mol%, 0.5 mol%

and 1.6 mol%

O20.01 mol%, 0.02 mol%

and 0.05 mol%

Moisture (H2O) in Gas 0.12 mg/L and 0.55 gm/L

Ambient Temperature 15 °C to 30 °C

Pipeline Pressure 720 psi and 900 psi

Typical Gas Flow inPipeline

Min.: 254 mmscfd; Max.: 1,114 mmscfd

Typical Pipeline Diameter

40”

300 ml glass beakers containing the appropriate test water.Sodium sulfite (Na2SO3) oxygen scavenger, in amountstypically specified in international hydrostatic testingstandards, was used in all tests that required the use of anoxygen scavenger. The glass beakers containing the samplesand the test solution were then inserted into the autoclavecompartments. Nitrogen gas was purged continuously inthese autoclaves for the entire length of the experiment toensure no ingress of oxygen thus simulating hydrotestingfield conditions. Flash drying of samples was performedusing a hot air gun and slow drying was achieved by leavingthe sample in open air to dry. These drying conditions wereintended to simulate field drying practices using methanoland hot air, respectively.

At the completion of each test set, the samples wereremoved, cleaned with distilled water and then driedaccording to the procedure shown in the test matrix. Aftercomplete drying, the appearance of the exposed surfaces ofthese samples was documented using stereomicroscopy. X-ray diffraction analysis was also performed, on the surfacesof all tested samples. This was conducted to characterize thechemical composition of surface deposits formed on thesurfaces. Bacterial analysis by testing of surface depositsformed on the steel exposed surfaces was also performed onsamples subjected to one and four week test durations.

Thermodynamic Modeling Analysis

Thermodynamic modeling analysis was performed using theFacility for the Analysis of Computational Thermodynamics(FACT) modeling software to perform all thermodynamiccalculations. Table 2 shows the data points that were usedin this analysis.

RESULTS AND DISCUSSION

Characterization of Black Powder and Mill Scale

Table 3 shows XRD analysis results of mill scale and blackpowder samples. It is clear from this table that the onlycommon compound in mill scale and black powder ismagnetite-Fe3O4. The magnetite-Fe3O4 found in blackpowder can originate from several sources acting incombination or separately: (1) Corrosion of steel in lowdissolved oxygen environment such as that found in a SalesGas pipelines environment (refer to reactions 6 and 7), (2)Bacterial-induced corrosion due to the presence of ironoxidizing and acid producing bacteria (IOB and APB,respectively), and (3) Conversion (by oxidation inside thepipeline) of iron sulfide-FeS and siderite-FeCO3 during adry cycle experienced inside the pipeline. Mechanicaldegradation of mill scale can also be a minor and shortlived source of magnetite-Fe3O4. Siderite-FeCO3 is a typical

corrosion product of CO2 induced corrosion (see reactions2 and 3)10, 11. Without moisture the reaction of these gases(at pipeline temperatures) is kinetically limited and thereforewill not lead to corrosion14. The fact that black powderexhibited siderite-FeCO3 is conclusive evidence that thepipelines from which the black powder was collectedexperienced water condensation on their internal walls.

X-ray florescence analysis revealed the presence of minorcontainments such as salts, sand, metal debris (from erodedequipment), elemental sulfur and mercury. These minorcontaminants make up less than 15 wt% to 20 wt% ofblack powder. Elemental sulfur was detected in all blackpowder samples in the range 3 wt% to 14 wt%.

The detected small amounts of elemental sulfur couldhave originated from the oxidation, inside the pipeline, ofsmall amounts of H2S and/or FeS as per the followingreactions:

2H2S + O2 → 2H2O + 2S (elemental) (8)3FeS + 2O2 → Fe3O4 + 3S (elemental) (9)

Scanning electron microscopy examination of the steelplate in cross section revealed that a mill scale thickness ofapproximately 8 μm as can be seen in Fig. 4. Examinationof the mill scale in planar view using stereomicroscopy

Table 3. Main chemical compounds of mill scale and black powder collectedfrom Sales Gas pipelines


Main Compounds

Black Powder Magnetite-Fe3O4, Goethite-FeOOH,Lepidocrocite-FeOOH and Siderite-FeCO3

Mill scale Magnetite-Fe3O4, Hematite-Fe2O3 andWuestite-FeO

Fig. 4. Shows SEM image of a cross sectional view of typical mill scale foundon the samples used in this study.


revealed that the mill scale is cracked and does not providecontinuous coverage to the steel substrate, as can be seen inFig. 5. It is at the bare steel-mill scale interface thatcorrosion takes place leading to popping off of the millscale. Similar SEM examination showed that black powderis composed of very fine jagged particles as shown in Fig. 6.X-ray diffraction analysis determined that the averageparticle size of black powder is in the nanometer range (lessthan 100 nm).

Seven Vickers microhardness measurements conductedusing 200 gm on mill scale; pipeline steel and black powderrevealed average hardness values of 585 Vickers hardnessnumber (VHN), 179 VHN and 599 VHN, respectively. It isthe jagged shape of black powder particles coupled with itshigh hardness which makes black powder very erosive tomany engineering materials.

A limited number of the collected black powder samples

were analyzed for SRB, general aerobic bacteria (GAB) andnitrogen utilizing bacteria (NUB) using an in-housedeveloped conventional cultivation media. In addition tothese types of bacteria, the same samples were also analyzedfor acid producing bacteria (APB) and iron oxidizingbacteria (IOB) using DNA analysis techniques at the GTI-USA. Sulfate reducing bacteria, IOB and APB bacteria areknown for causing microbiologically induced corrosion(MIC) of steel in the presence of condensed moisture(water)1. These results indicate that, in the analyzed blackpowder samples, microbial corrosion is a low potentialsource and if it were to occur it would be due to APBand/or IOB13. The absence of SRB is in agreement with theabsence of FeS in the chemical composition of blackpowder.

Sales Gas Analysis

Table 4 shows measured dew point temperatures at 130 psiusing the panameteric analyzer method for gas samplescollected at different sampling points. Calculated moisturecontent at 130 psi and dew point temperatures at linepressures are also included in this table. It is clear from thisTable that all samples, except for one gas sample collectedfrom sample point No. 6, have a calculated moisturecontent which exceeds the maximum moisture content limitof 0.112 mg/l (7 lb water/mmscf) typically specified by SalesGas pipelines operators. Figure 7 shows typical temperaturevariations experienced in the Eastern Province of SaudiArabia. Comparison of this Figure with Table 4 shows thatsome dew point temperatures, at line pressure, are below orequal to ambient temperatures experienced in the winterseason. This points out to the high potential for theoccurrence of moisture condensation, on the inner walls ofpipelines, during the winter season. Direct measurement ofmoisture content using the methanol scrubbing methodshowed similar moisture contents than exhibited in Table 4.

Fig. 5. Shows stereomicroscopic image of a planar view of typical mill scalefound on pipeline plate steel.

Fig. 6. Shows SEM an image of black powder collected from Sales Gaspipelines.

Fig. 7. Shows typical temperature variation experienced in the Eastern Provinceof Saudi Arabia. Note the number of days below the red dashed line whereambient temperature is low enough for condensation to occur at the high dewpoints exhibited in Table 4.


Table 5 shows measured levels of the gas componentsthat are deemed critical to internal corrosion of Sales Gaspipelines. For comparison purposes typical Sales Gasspecifications adopted by many gas line operators isincluded. It is clear from this Table that the O2, H2S andCO2 measured levels are within typical Sales Gasspecifications. In contrast, the measured moisture contentsexceed the maximum limit of 0.112 mg/l.

Effects of Hydrotesting Parameters

X-ray diffraction analysis was used to examine all samplesexposed to the simulated hydrostatic test. Bacterial analyseswere also conducted on the deposits formed on the surfacesof the steel samples. Our findings show that laboratorysimulated hydrotesting did not lead to the formation ofmagnetite-Fe3O4 and goethite-FeOOH iron oxides that arethe predominant species found in black powder. Also, it wasfound that, drying conditions are the most influential indetermining whether or not hematite-Fe2O3 can form at themill scale-steel interface leading to mechanical degradationof the mill scale. For example, rapid flash drying, whichresembles drying with methanol in the field, was found toeliminate the formation of hematite-Fe2O3 whereas slow

drying, which resembles drying with hot air in the fieldproduces hematite-Fe2O3.

Thermodynamic Modeling Analysis

The thermodynamic modeling analysis showed that blackpowder is made up of various forms of corrosion products,namely iron oxides and hydroxides as well as ironcarbonates. These iron phases generated inside the pipelineas a result of the internal corrosion of Sales Gas pipelines.In addition, this analysis has shown that mill scale isthermodynamically stable (does not degrade) in Sales Gasenvironment and therefore is not a source for blackpowder14.

CONCLUSIONS

Black powder is a worldwide phenomenon experienced bymost, if not all, gas pipeline operators. Black powder isregenerative and is formed inside natural gas pipelines as aresult of corrosion of the internal walls of the pipeline.More specifically, by reactions of iron (Fe) present inferrous pipeline steel with condensed moisture containingoxygen (O2), hydrogen sulfide (H2S), and carbon dioxide(CO2). These chemical species are benign in dry Sales Gas,but can become corrosive when dissolved in water moisture.In Sales Gas pipelines, black powder is composed mainly ofiron hydroxides, iron oxides and iron carbonates.Contaminants such as sand, dirt, hydrocarbons, elementalsulfur and metal debris typically make up 20 wt% of blackpowder. The jagged shape and high hardness of blackpowder make it very erosive to many engineering materialssuch as pipeline control valves. Field hydrotesting and millscale have minor and short term contribution to blackpowder formation. It has been shown that thermodynamic

Table 5. A summary of typical Sales Gas specification and measured levels forcomponents that are deemed critical to internal corrosion of Sales Gas pipelines

Table 4. Measured dew point temperatures, at two different dates, using the panameteric analyzer and the corresponding calculated moisture contents*

SamplePoint

Measured Dew Point °C at 130 psi

Calculated MoistureContent (mg/l)

Line Pressure (psi)Dew Point °C

at Line Pressure

July/06 Feb/06 July/06 Feb./06 July/06 Feb/06 July/06 Feb/06

1 -11 -18 0.23 0.13 900 900 15.8 7.0

2 -3 -7 0.43 0.32 900 900 26.0 21.1

3 -17 -19 0.14 0.12 900 900 8.3 6.0

4 -17 -18 0.14 0.13 900 900 8.3 7.2

5 -14 -11 0.18 0.23 740 720 9.1 12.4

6 -20 0.0 0.11 0.55 740 720 2.0 26.4

7 -11 -15 0.23 0.17 740 720 12.8 7.8

*Maximum moisture content in typical Sale Gas specification is 0.112 mg/l which is equivalent to dew points of 5 °C, 2.2 °C and 1.9 °C @ 900 psi, 740 psi and 720 psi, respectively.

ComponentTypical Sales Gas

Specification(Maximum Limits)

MeasuredLevels

H2S (ppm) 16 1 - 15

O2 (mol%) 0.02 0.01 - 0.03

CO2 (mol%) 3 < 1.62 mol%

Moisture (mg/l) 0.112 0.12 - 0.55


modeling analysis is a powerful tool in predicting theformation and stability of various iron phases a in Sales Gasenvironment.

R&DC has recently initiated research projects to preventand manage the impacts of black powder in Sales Gaspipelines. We will review the results of these projects whichwill be the subject of another article.

ACKNOWLEDGEMENTS

The author would like to thank Saudi Aramco for thepermission to present and publish this paper. Special thanksto J. Perez of the Pipelines Department for providing allblack powders samples, coordinating the thermodynamicand the gas analyses and for the many useful discussions.Special thanks go also to S. Jutaily, S. Zaidi, E. Tuzan, A.Shehry, H. Ghassan, M. Saleh, P. Sanders, and C.Braithwaite, M. Shafei and A. Nowaishi, A. Al-Haji, G.Jamison, K. Dossary and O. Al-Olayan of the R&DC, andM. Omairy and A. Kawaie, Consulting ServicesDepartment, and Yousef Farraj of Southern Area LabsDivision (SALD) for their analytical and laboratory support.The author would also like to thank A. Lewis, S. Duval andA. Abdulhadi of the R&DC for the many usefuldiscussions.

REFERENCES

1. Baldwin, R.M.: “Black Powder in the Gas Industry-Sources, Characteristics and Treatment,” GMRC, ReportNo. TA97-4, May 1998.

2. Baldwin, R.M.: “Black Powder Control Starts Locally,Works Back to Source,” Pipeline & Gas Industry, April1999, pp. 81-87.

3. Baldwin, R.M.: “Black Powder Problem will Yield toUnderstanding, Planning,” Pipeline & Gas Industry,March 1999, pp. 109-112.

4. Tsochatzidis, N.A. and Maroullis, K.E.: “Methods HelpRemove Black Powder from Gas Pipelines,” Oil & GasJournal, Vol. 105, No. 10.

5. Arrington, S.: “Pipeline Debris Removal RequiresExtensive Planning,” Pipeline & Gas Journal, November2006, pp. 61-62.

6. Godoy, J.M., Carvalho, F., Cordilha, A., Matta, L.E. andGodoy, M.L.: “(210) Pb Content in Natural Gas PipelineResidues (“Black Powder”) and its Correlation with theChemical Composition,” Journal of EnvironmentalRadioactivity, 2005, pp. 101-111.

7. “Corrosion Solutions for Gas Transmission Pipelines,”Honeywell Solution Note, www.honeywell.com/ps.

8. Sridhar, N., Dunn, D.S., Anderko, A.M., Lencka, M.M.and Schutt, H.U.: “Effects of Water and GasCompositions on the Internal Corrosion of GasPipelines-Modeling and Experimental Studies,”Corrosion, Vol. 57, No. 3, 2001, pp. 221-235.

9. Lyle, F.F.: “Carbon Dioxide/Hydrogen Sulfide Corrosionunder Wet Low-Flow Gas Pipeline Conditions in thePresence of Bicarbonate, Chloride and Oxygen,” PRCIFinal Report PR-15-9313, 1997.

10. Craig, B.: “Corrosion Product Analysis - A Road Mapto Corrosion in Oil and Gas Production,” MaterialsPerformance, August 2002, pp. 56-58.

11. West, G.D., Birosca, S. and Higginson, R.L.: “PhaseDetermination and Microstructure of Oxide ScalesFormed on Steel at High Temperature,” Journal ofMicroscopy, Vol. 217, No. 2, February 2005, pp. 122-129.

12. Hudson, R.M.: “Pickling of Hot Rolled Strip: AnOverview,” I&SM, September 1991, pp. 31-39.

13. Zhu, X.: “Bacterial Analysis of Saudi Aramco BlackPowder Samples,” GTI Report No. 080306.

14. Davis, R.B. and Calabretta, D.: “ThermodynamicAnalysis of Formation of Black Powder in Sales GasPipelines,” Purchase No. 6510217086 for SaudiAramco, March 2007.

BlackPowder.pdf

Documents

Transcript of BlackPowder.pdf