HNBR for use in oilfield applicationsby John E. Dato, E.C. Campomizz.i and D. Achten, Lanxess

In fundamental terms, fully hydrogenated NBR can be de-scribed us a copolymer consisting of randomly distributed se-quences of ethylene and acrylonitrile monomers. The intrinsiccombination of good heat, extreme oil and chemical resis-tance, coupled with outstanding physical properties and easeof processing for HNBR, can be attributed to its compositionand structural arrangement.

The use of HNBR for rubber articles such as stators (drillingmotors and progressive cavity pumps), packers, blow out pre-ventors and drill bit seals, can extend the lifetime of the arti-cles, thereby reducing the maintenance frequency or extendingthe replacement cycles for those parts. This benefit can poten-tially translate into substantial operational cost savings withoutcompromise to safety.

Furthermore, advances in technology have permitted thedevelopment of new grades. New low viscosity polymers basedon Therban AT (Advanced Technology) provide polymers thatcan be processed as easily as regular nitrile polymers (NBR).while retaining the advantageous properties of HNBR. Otberdevelopments in carboxylate technology have allowed develop-ment of Therban XT (HXNBR), which offers the advantages ofcarboxylated NBR. but with the improvements in heat resis-tance and abrasion (due to the reduced stiffness ofthe polymerbackbone) afforded by the hydrogénation of the polymer back-bone. By utilizing the new HNBR polymers, unprecedentedlatitude of compounding, as well as novel ways of processing,can be attained. This, in turn, opens the door for new dimen-sions of design. Examples will be given in the article.

Discu.ssionThe development of new elastomers with improved perfor-mance profiles h:is hecome increasingly important, paiiicu-

Figure 1 - molecular structure of HNBR

Structural elements of hydrogenated nitrile rubber

Pendant nitrile group Residual double bond Polyethylene sequence

Oil resistance Crossiinking efficiency Chemical inertnessChemicai-heat Dynamic crystallization

resistance

larly for rubber parts used in the oil industry.New, demanding methodologies have emerged, such as

horizontal drilling and smart well techniques, in combinationwith increasingly advei"se conditions of deeper wells andhigher temperatures. The more extensive use of corrosion in-hibitors to protect production equipment from unpredictablemixtures of hydrocarbons, possibly containing sulfur. H-,S.CO2, CH4, and the extensive use of steam and brine injectionsto improve yields from even the smallest oil ptx:kets haveraised demands on standard elastomers to an extent that theyare reaching their performance limits.

Consequently, equipment containing seals, stators, packersand other parts must be maintained or replaced more frequent-ly, leading to increased cost with respect to both parts and tooperational down-time. It is readily apparent that reliabilityand durability of equipment become limiting factors for thetotal output and overall return for each drilling operation.

A number of limiting performance criteria for several rub-ber parts used in the oil well services industry have been iden-tified. These are:

• Resistance to high temperature and to aging:• resistance to swelling by aggressive fluids and gases;• resistance to explosive decompression;• mechanical properties and resistance to deformation at

elevated temperatures;" abrasion and wear resistance under extremely adverse

conditions: and• processing properties to allow a greater freedom of com-

pounding, and new part design and production techniques.It is well known that HNBR is an oil resistant polymer that

is well suited to deliver the pertormance criteria needed by theoil well sector. This outstanding property profile is attributableto the saturated polymer backbone in combination with thehighly polar and inert acrylonitrile functional group. Startingfrom NBR. still the workhorse polymer for the oil industry.HNBR has a similar oil resistance as NBR. but with signifi-cantly improved chemical and heat resistance as well as im-proved physical properties over a wide temperature range.Through the hydiogenation process the double bonds of NBRare eliminated, the typical sites susceptible to chemical andoxidad ve attack. At the same time, the irregularly placed buta-diene units are transfonned into polyethylene sequences,which gives HNBR its ability to reversibly crystallize understrain, resulting in physical properties comparable to naturalrubber. Hence, the selective hydrogénation of the doublebonds in acrylonitrile-butadiene rubber (NBR) produces aspecialty elastomer, hydrogenated acrylonitrile-butadiene rub-ber (HNBR), which may be formulated to produce a materialconveying an excellent balance of properties including me-chanical and dynatnic, as well as improved resistance to hotair, oils, chemicals and abrasion.

Therban is characterized by a combination of properties thatmake rubber goods resistant to service conditions found in oil

2 8 RUBBER WORLD

Table 1 - typical properties of HNBRvulcanizates

Hardness, durometerTensile strength, MPaElongation at break, %Modulus, MPa

M200

Rebound resilience, %Compression set, %70 hrs./23°C70hrs./150°CAbrasion loss, mm^, DIN 53 516

50=A1550

34.5

630

30

tototo

totototo

1520to

45500

20454050

60

exploration ;ind production environmenls.Typical vulcanízate properties for HNBR are shown in table

I. Appropriate compounding techniques and selection of themost suitable TTierban polymer enable the properties of thevulcanizates to be adapted to specific requirements. HNBRvulcanizates also exhibit good resistance to alkahne solutionsand dilute acids. The resistance to a caustic soda solution(25%) at 100°C and to a dilute hydrochloric acid solution(18%) at 50°C is very good. Generally, the chemical and oxi-dative stability improve with increasing degree of hydrogéna-tion.

Síahility under oilfield conditionsRubber articles for oilfield application must withstand bothmechanical wear and chemical attack by drilling mud andother aggressive fluids. Depending on the actual well condi-tions, the parts may be exposed to mixtures of oil with acidsand amines, as well as hydrogen sulflde, methane and carbondioxide. In addition, high pressure and temperature conditionsLire encountered, especially as the well depth increases.

Resistance to hydrogen .sulfide and corrosion inhihiiorsHydrogen sulfide, which occurs in crude oil and natural gaswells, is an aggressive media encountered with increasing

frequency. Other substances found in the service environmentthat tend to aggressively attack rubber articles include aminecorrosion inhibitors, carbon dioxide and acids.

For the test results described below, use was made of mix-tures consisting of diesel oil. sour gas, water and amine-basedcorrosion inhibitors NACE A and NACE B.

Figure 2 shows that the retention of tensile strength ofHNBR based compound is superior to that of standard FKM,NBR and XNBR when aged at 150°C in a mixture consistingof diesel oil. sour gas and water.

Similarly, good retention of tensile strength for HNBR isobserved when the corrosion inhibitors NACE A (figure 3)and NACE B (figure 4) are added to the mixtures. In thesecases, the properties of HNBR remain substantially un-changed, whereas those of FKM, NBR and XNBR suffer sig-nificant reduction in tensile strength. For the compounds basedon these polymers, the tensile at break after aging is in therange of 7-8 MPa, representing a loss in tensile in the 50-80%range. On the other hand, the tensile at break for the HNBRbased compound is still in the order of about 18 MPa, repre-senting a loss in tensile of about 30%.

Figure 3 - resistance to sour gas, diesel oiland water + 1% NACE A (aged 7d @ 150 C)

Tensile strength

30

UnagedAged

Therban FKM NBR XNBR

Figure 2 - resistance to sour gas, diesel oiland water (aged 7d ® 150 C)

Tensile strength UnagedAged

Therban FKM NBR XNBR

Figure 4 - resistance to sour gas, diesel oiland water + 1% NACE B (aged 7d @ 150 C)

Tensile strength UnagedAged

Therban FKM NBR XNBR

AUGUST 2007 2 9

Results obtained with the oil soluble NACE B (figure 4)show tbe same behavior as observed when water-solubleNACE A is used.

In tbe described tests. Therban elastomer was comparedwith FKM, NBR and XNBR, aJI of which are known to with-stand heat and/or oil swells. Commercially available elasto-mers were chosen for the tests. In the case of FKM, a bisphe-nol crosslinked compound was used.

To improve properties wherever swelling and aging incrude oil is a problem, the use of fully hydrogenated highACN content HNBR, such as Therban A 4307, is stronglyrecommended.

Resistance to explosive decompressionRubber articles used in the oil industry are also exposed toextremely high pressures. At these extreme pressure condi-tions, low molecular weight hydrocarbons, as well as othergases, such as carbon dioxide and hydrogen sulfide, are con-siderably more soluble in the rubber article than is the case atnormal pressures. Diffusion of the gases into the article occursuntil equilibrium is establisbed.

At a sudden pressure drop, as might result through a suddenchange in the operating conditions, the dissolved gases tend to

Figure 5 - explosive decompressionresistance of various poiymers

D)

^ 4

Î 3

Il 1

HNBR NBR FKM

Figure 6 - effect of explosive decompressioncycle in CO2 on tensile strength

escape rapidly from the rubber, causing internal destruction ofthe part. The resistance to this "explosive decompression" ispolymer and compound dependent.

Figure 5 shows that vulcanizates based on HNBR elastomerare highly resistant to explosive decompression. Dry carbondioxide at 5.2 MPa (750 psi) was used in the test to evaluateexplosive decompression resistance. Tbe carbon dioxide gaswas introduced into the pressure vessel containing the testspecimens. Exposure time was 24 hours at room temperature.aiter which the specimens were explosively decompressed byopening an exhaust valve, allowing the pressure to drop from5.2 MPa to atmospheric pressure in less than 10 seconds.

The criteria used to rank the compound performance underthese test conditions were resistance to blistering and destruc-tion, as well as retention of physical properties, includingtensile strength at break, elongation at break and hardnesschange.

Figure 6 shows the effect of explosive decompression test-ing on tensile strength. The specimens were aged as described(after aging in CO2 @ 23°C, 5.2 MPa for 24 hrs.) and thenwere tested one hour after the decompression step. These re-sults showed an even greater differentiation among the poly-mers tested.

It is generally recognized that explosive decompression isimproved by the following:

• The solubility of gases in the polymer is low;(—> high ACN content is recommended);

• the polymer should have high impenneability to gases,(—> high filler loading);

• tbe physical properties are as high as possible,( ^ high tear resistance, tensile strength).

For most elastomers, permeability and solubility can beadjusted by means of compounding techniques. Highly filledcompounds lead to better results in explosive decompressiontests than lightly filled conipi)unds.

Advanced technology Therban ATIn order to meet performance requirements, compounds tormany oilfield applications are formulated to high durometerusing high levels of fillers. The need for high filler levels oftenresults in high compound viscosities, which are contrary togood processing requirements/needs. Typically, these prob-lems are overcome by the introduction of plasticizers andprocess aids; however, these additives are often detrimental toproduct performance, since plasticizers can be extracted andexchanged by media, and they influence permeation and solu-

Table 2 - advanced technology Therban ATgrades

Product rangeACN (%) ML

213434394343

- typical properties1+4 at 100°C

393939393939

RDB (%)<0.9<0.9

4.0<0.9<0.9

5.5

30 RUBBER WORLD

bility of gases.The most recent breaktiirough in HNBR technology has

been the development of a new class of low viscosity HNBRprixiucts by Lanxess, now available commercially as TherbanAT. Previously, ultra low viscosity HNBR polymers wereimpossible to manufacture because of limitations in the avail-able viscosity for NBR feedstocks. Compared with conven-tional HNBR products having a raw polymer Mooney viscos-ity in the nominal range of 65, these new Therban AT productshave a typical raw polymer Mooney of 39. They are availablein a wide range of ACN and residual double bond (RDB) lev-els, as shown in table 2. These products have clearly demon-strated the following advantages over regular viscosity HNBRgrades:

• Low molecular weight (low viscosity) provides improvedpnK'essability. including faster mixing (shorter black incorpo-ration times); significantly better flow and faster moid filling(shorter cycle times); improved extrusion rates and extrudateshaving smoother surfaces iind sharper edges.

• Narrower molecular weight distribution helps to maintainexcellent physical strength properties, despite a drop in mo-lecular weight.

Figure 7 - processing window for Therban AT

Typical viscosity and shear rate processing windows

100 ^

10 >-

1 •-

Viscosity [kPa s]

BOPs

— standard HNBR— AT HNBR

Seals'Hoses'cables/stators

Compression Drill bit " N ^ ^ " ' ^molding. seals ^^iíeeáonbuilding Mixing Extmsion molding Shear rate

i A i i [1/s]1 10 100 1,000

•HNBR produced using advanced technologyprovides the broadest processing flexibility

Figure 8 - polymer and compoundviscosities for Therban AT

Mooney viscosity (ML 1+4 at 100'C)HNBR AT 11 /Standard HNBR "

120

Polymer Compound

Table 3 - effect of N-330 carbon black levelon vulcanízate properties

Therban AT40 phr N330

Mooney viscosity(ML 1+4, 100°C)M-100 (MPa)Tensile strength (MPa)Ultimate elongation (%)Hardness (duro A)

57

5.626.6273

64

50phrN33069

7.527.825669

HNBR40phrN330

101

6.527.423766

• Elimination or reduction oí plasticizcr is possible to im-prove heat aging, compression set, physical properties andadhesion.

• Processability can be maintained at higher filler loadings,thereby enabling an extended hardness range and providingcost savings potential through higher compound extension.

The advantages in processing properties for Therban AT areillustrated in figure 7. Compared with standard HNBR, Tber-ban AT shows lower viscosity levels through the entire rangeof shear rates typically encountered in rubber prtx-essing.

Figure 8 compares a stand:ird HNBR with Therban AT,both containing 34% ACN, 0.9% RDB. Therban AT has asignificantly lower raw polymer viscosity compared with stan-dard HNBR. This translates to a significantly lower compoundviscosity as well.

Comparison of vulcanizóte properties for Therban ATA study was conducted to compare various compound andvulcanizate properties for standard HNBR and Therban AT.Both polymers contain 34% ACN. 0.9% RDB. The resultsshown in table 3 and figure 9 demonstrate that, at a constantloading of N-330 carbon black, Therban AT provides a dra-matic reduction in compound viscosity. Modulus, hardnessand compression set of Therban AT can be easily adjusted bya minor variation in eitber filler loading or peroxide level to

Figure 9 - effect of peroxide level oncompression set

Effect ol peroxide dosage on compression set.70 hrs. @ 150"C

25

coIf)

0Q.EoO

Standard HNBR HNBR AT HNBR AT7.5 phr peroxide 7.5 phr peroxide g.o phr

(34% ACN, peroxide= 0.9% RDB

AUGUST 2007 3 1

reach the same or even better performances than standardHNBR without losing the advantage of easier processing.

The key benefits for using new Therban AT are summa-rized in figure 10. Therban AT can be utihzed in numerousoilfield apphcations. A list of potential applications and bene-fits is summarized in figure 11.

Carboxylated technology Therban XTHydrogenated carboxylated acrylonitrile-butadiene (HXNBR)provides vulcanizates possessing outstanding mechanicalproperties (tensile, elongation and tear) combined with excel-lent property retention at high temperatures. In addition, thevulcanizates exhibit excellent abrasion resistance and adhesivestrength, as well as improved hot air aging resistance overcarboxylated nitrile. In severe oilfield environments, HXNBRis recommended for numerous applications, including drill bitseals, ram packers, pipe wipers and seals requiring enhancedmetal adhesion.

Lanxess produces a commercial HXNBR polymer identi-fied as Therban XT VP KA 8889. It contains 34% acrvlonitrile(ACN), 5% carboxylic acid groups and 3.5% residual doublebond (RDB) content. The strucmre of HXNBR is illustrated infigure 12.

Figure 10 - Therban AT summary of benefits

Summary of benefits of advanced technology HNBR• Narrow molecular weight distribution combined with low

viscosity- Retention of excellent physical properties with improvedprocessing properties

Improved mixing, better flow, faster mold filling, shorter cycletimes

- Cost reduction, lower injection/extmsion pressureReduction or elimination of plasticizer

- Significantly improved physical properties, improvedmetal adhesion, lower compression set, low plasticizerextraction or volatilization during service

• Proœssability even at significantly higher filler loads- Extended hardness range, cost savings potentialfrirough higher compound extension, improved explosivedecompression resistance

Figure 11 - potential oilfield applicationsfor Therban AT

ApplicationsSealsGasketsO-ringsHosesBOPsCablesStatorsPackers

Benefits-*• Retention force-*• Hardness-»Surface quality

^ •*• Flame resistance* Loading, ED resistance•*• Volume flow- Cycle times-• Metal adhesion& Intricate shapes

If viscosity is a problem use Advanced TechnologyHNBR alone or in combination with standard HNBR toselectively customize the properties of your compound.

Hydrogénation of carboxyiated nitrile (XNBR) to produceHXNBR achieves the following vulcanizate improvements:

• Mechanical properties (tensile strength and elongation)from 23''C to elevated temperatures (170°C);

• tear resistance from 23°C to I70°C;• Pico abrasion resistance;• adhesive strength to substrates such as nylon at 125°C;

and• hot air oxidation resistance.

HXNBR can be formulated alone or in blends with HNBR totarget ranges within this set of outstanding properties.

Resistance to abrasionResistance to mechanical wear is another basic requirement forelastomer parts used in the oil industry. HNBR is recognized tobe superior to most other elastomers. It is capable of providinglong term service at high temperatures up to lóS^C and shortterm service up to 185°C. If severe wear is the main reason forfailure of parts, the use of Therban XT, a new HNBR gradecontaining 5% carboxyl groups, is recommended.

To further boost physical properties, Therban XT can becombined with zinc diacrylate (ZDA). Blends containing ZDA(available under the brand Therban ART) can achieve a

Figure 12 - hydrogenated carboxyiatednitrile butadiene rubber

COOH

yCN

33%Acrylonitrile

5%Cartxjxyl

3.5%Residual

double bonds

Figure 13 - comparison of physicalproperties - standard HNBR, HXNBRand HXNBR in combination with ZDA

HardnessTear strengthDieB®

Tear strength ¿Die B

Ultimate tensile

^ Ultimate/' elongation

Scorch 6 @ 125''CV. ' ^ l ^ ^ ^ Stress @ 100%

Pico abrasive index

HXNBR • +ZDAHXNBRHNBR

3 2 RUBBER WORLD

unique combination of ptiysical properties, inciuding tensilestrengths of 40 MPa. 2iX)% elongation at break. DIN abrasionvalues < 50 mm-' and durometer A hardness of 85-95.

Figure 13 compares some basic physical properties that canbe achieved using standard HNBR. Therban XT and TherbanXT in combination with ZDA. Therban XT provides highhardness and modulus, high tear resistance and high abrasionresistance. This combination ot properties is useful in variousoilfield applications, including drill bit seals, ram packers, andpipe wipers.

Resistance to oilfield fluidsIt has been shown that Therban XT ean provide a uniquecombination of vulcanizale properties for oilfield compo-nents; however, it is also important to consider the perfor-

Krynac 3345CKrynac VP KA

8871Therban XT

VP KA 8889Therban B 3627Therban ART

VP KA 8798Dyneon FKM

FC2123Vulkan ox

HS/LGNaugard 445Aerosil 972VCarbon black

N650Carbon black

N990HiSil915Silane A-172

DLC (72%)Armeen 18DDOPTOTMStearic acidVanfre VAMDiak #7StruktolZP1014Zinc oxide

(Kadox 920)Spider sulfurVulcup 40KEVulkacit

CZ/EGCVulkacit

Thiuram/C (D)Calcium

hydroxideHP-XL

Maglite DTotal (phr)Specific gravity

Table 4

NBR

100

1

55

5

0.5

5

0.4

2

2

170.91.193

LWSNBR

100

1

55

5

0.5

5

0.4

2

2

- compounding formulations

100XT

100

1.5

55

0.5

10

1.252.5

6

9

170.9 185.751.193 1.177

65XT/35B3627

65

35

1.5

55

0.5

10

1.252.5

6

9

185.751.174

35XT/65B3627

35

65

1.5

55

0.5

10

1.252.5

6

9

185.751.171

0XT/100B3627

100

1.5

55

0.5

10

1.252.5

6

9

185.751.169

100B3627/Aerosil

100

1.555

0,5

10

1.252.5

6

9

185.751.21FKM

100B3627/

HiSil

100

1.5

552

0.5

10

1.252.5

6

9

185.751.21

85 XT/30

ART

85

30

1.5

X

0.5

10

1.252.5

6

9

175.751.135

FKM

100

30

6

3139

postcured 6 hours at 230°C

manee of HXNBR in Viirious aqueous fluids. For example, itis generally recognized that XNBR. due to its caiboxyl func-tionality, exhibits higher water swell than NBR. A study wa.sconducted to assess the swelling characteristics of Therban XTcompared with other typical oilfield polymers. The other poly-mers included .standard NBR. low-water-swell NBR. standardHNBR and FKM. In addition. Therban XT was evaluated invarious blend ratios with standaid HNBR and also in a blendwith Therban ART. For this study, both carbon black and sili-ca tillers were evaluated. The formulations used for the designstudy are shown in table 4.

Stress-strain properties were assessed for each of the com-pounds. Results are shown in figure 14. All compounds weredesigned to achieve a similar haidness range. All of the NBRand HNBR formulas show very high tensile strengths (> 20

^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ M Pa ) compared to theFKM formula (12 MPa).

AM vulcanizates wereimmersed in distilledwater at lCWC for periodsof 70, 168 and 504 hours.The values for volumeswell in distilled water areshown in figure 15. All ofthe HNBR and HXNBRvulcanizates show verylow volume changes. Theyprovide water swell valuesthat are equivalent to, orbetter than, the NBR vul-canizates. The fumed sili-ca filler shows particularlylow water swell. The FKMvulcanizate shows veryhigh volume change alter504 hours aging.

All vulcanizates wereimmersed in a solution of2% calcium chloride anddistilled water to simulatebrine environments en-countered in oilfield ap-plications. The vulcani-zates were aged at IOO°Cfor periods of 70, 168 and504 hours. The values forvolume swell in calciumchloride are shown in fig-ure 16. All ofthe HNBRand HXNBR vuicanizatesshow low volume chang-es, comparable to standardandiow-water-swellNBR.The FKM vulcanizateshows particularly highswell after aging 504hours in calcium chloride

AUGUST 2007 33

solution compared with HNBR.Since NBR is still considered to be the workhiorse polymer

for the oil industry, it can be concluded that HNBR, and par-ticularly Therban XT. are both viable alternatives for hightemperature environments requiring excellent resistance towater and brine media.

In order to assess the effect of oi! swell. HNBR and FKMvulcanizates were immersed in IRM 903 at 150°C for a periodof 70 hours. The NBR vulcanizates were not tested at 150°C.The values for volume swell in IRM 903 are shown in figure17. HXNBR shows slightly lower volume change than stan-dard HNBR, even though the ACN contents are approximate-ly 33% and 36%. respectively. The lower volume change forHXNBR is indicative of the higher crosslink density andhigher modulus which is achieved via ionic crosslinking with

Figure 14 - stress-strain properties

80

70

60

50

40

30

20

10 IICECO

CDCO

Ü3

^ ë glO lO - ^

CÖ i*5 oHardness P Tensile (MPa)(durometer A)

lElongation (%-MO)

Figure 15 - volume change in distilied water

70 tirs. ,n 168 hrs. lOOX \s 504 tirs. 100X

HXNBR. As expected, the volume changes for blends ofHXNBR and standard HNBR show intermediate values.Among the polymers tested, the volume change is lowest withFKM; however, it should be noted that no HNBR polymerswith high ACN content were tested in this series. The oil swellfor HXNBR can be further improved by blending with anHNBR containing 43% ACN content.

In order to assess wear characteristics, the NBR, HNBR.HXNBR and FKM vulcanizates were tested for Pico abrasion.The values for abrasive index are shown in figure 18. A highabrasive index translates to low abrasion volume loss. All ofthe vulcanizates that contain HNBR clearly show superiorabrasion resistance compared with NBR and FKM. On top ofthat, for example, the compound containing only 35 phr of

Figure 16 - volume change in 2%calcium chloride

70hrs. 100X 504 hrs 10OX

Figure 17 - volume change in IRM 903 oil

70hrs.150°C

3 4 RUBBER WORLD

HXNBR even shows a two-fold improvement in abrasion re-sistance compared to standard HNBR. The sample containingHXNBR and Therban ART shows the highest abrasion resis-tance of all samples tested.

From the results of this compounding study, it can be con-cluded that Therban XT provides high physical properties, lowvolume change in water and brine, low volume chLinge in IRM903 oil and excellent Pico abrasion resistance. Abrasion resis-tance can be further enhanced by using blends with TherbanART. Some of the key properties, and potential oilfield appli-cations, for HXNBR are:

• HNBR is recognized as a superior polymer for long-termservice at temperatures up to 165°C and for short-term use uptol85X.

• For severe wear applications, the use of HXNBR providesboth wear resistance and high temperature service.

• Enhanced physical properties and wear re.sistance areachieved when combined with Zn-diacrylates (ZDA):

- hardness of 85-95 durometer A;- tensile strength up to 45 MPa with elongation at break

200%- DIN abrasion < 50 mm-• HXNBR (as well as ZDA combinations) can be used in

applications requiring high dynamic stress, low abrasion andhigh modulus, such as drill bit seals, ram packer BOPs, pipewipers and rubber-to-metal bonded seals.

Some of the key properties for HNBR are:• Excellent physical properties and abrasion resistance at

elevated temperatures;• very good hot air and oil resistance;• good resistance to alkali and hydrogen sulfide;• very good resistance to "extrusion" and "explosive decom-

pression";• low water swell; and• good compression set and low temperature behavior.

This article has illustrated some of the many benefits that can

Figure 18 - Pico abrasion

3.500

3,000

be achieved by using HNBR elastomers. In addition to itsgood heat, oil, fuel and chemical resistance, Therhan providesa good combination of mechanical properties, tear strengthand abrasion resistance. Therban. with its new. low viscosityAT line, its carboxylated Therban XT and its zinc-diucrylatereinforced Therban ART. specifically addresses the needs ofstate-of-the-art oilfield technologies and demanding produc-tion methods that have to meet increasingly severe conditionsand adverse environments. Some typical applications of thewide variety of oilfield components in which the Therbanproduct range can be used include: stators (.drilling motor andpump); drill bit seals; blow out preventors (ram and annulartypes); packers: seals for exploration and production equip-ment (valve, wellhead, surface); pipe wipers; drilling hose(rotary, choke and kill); drill pipe protectors; oil and wear re-sistance cable jackets: diaphragms; and rubber-to-metal bond-ed seals

ConclusionsThe development of new elastomers with improved perfor-mance profiles has become increasingly important, particu-larly for rubber paits used in the oil industiy. New. demandingmethodologies have emerged, such as horizontal drilling andsmart well techniques, in combination with increasingly ad-verse conditions of deeper wells and higher tempei alures. Tliemore extensive use of corrosion inhibitors to protect produc-tion equipment from unpredictable mixtures of hydrocarbons,possibly containing sulfur. H2S. COi. CH4. and the extensiveuse of steam and brine injections to improve yields from eventhe smallest oil pockets have raised demands on standard elas-tomers to an extent that they are reaching their performancelimits. The use of HNBR for oilfield components can extendthe lifetime of the articles, thereby reducing the maintenancefrequency or extending the replacement cycles for those parts.These benefits translate into substantial operational cost sav-ings without compromise to safety.

Advances in polymer technology have enabled the intro-duction of new grades specifically addressing the needs of theoil-well industry. New low viscosity polymers based on Ther-ban AT (Advanced Technology) provide polymers which canbe processed as easily as regular nitrile polymers (NBR),while retaining or even improving the advantageous propertiesof HNBR. Advances in carboxylate technology have enabledthe development of Therban XT (HXNBR), which offers theadvantages of carboxylated NBR but with the improvementsin heat resistance afforded by the hydrogénation of the poly-mer backbone. ZDA-modified HNBRs (Therban ART) pro-vide excellent resistance to mechanical wear. By utilizingthese new HNBR polymers, unprecedenled latitude of com-pounding, as well as novel ways ot"processing, can be attained.This article has illustrated the performance profile and prop-erty improvements for new Therban polymers in various oil-field components. Typical application examples have beenrecommended. CED

This article is based on a paper given at a meeting of theRubber Division. ACS (www.rubber.org).

{continued on page 86)

AUGUST 2007 35