Inflatable packers brief introduction to rubber

Replacement
29 Wheeler Street
Inflatable
Belmont 6104
PH: +61 08) 9475 0700
Packers &
Fax: +61 (08) 9475 0770
Elements
Mob:0400346687
info@rripe.com.au
Pty Ltd ACN: 112472287
www.rripe.com.au
ABN: 81992154253
A brief introduction to Rubber and manufacture of Inflatable Packers
By: John Misson, Replacement Inflatable Packers and Elements Pty Ltd. August 2007
Rubber once solely produced from the sap of the Para Rubber Tree (Hevea braziliensis)
and still in wide use today, initially presents as a milky colloidal suspension, or latex. In
this state it is a naturally occurring hydrocarbon that may be called a polyterpene. This
elastic hydrocarbon polymer was greeted upon its arrival in Europe, with an admixture of
amazement and horror (some thinking its properties the work of the devil!).
Following significant research and experimentation during the nineteenth century, we
come today to nearly two dozen rubber types, some fully synthetic, others less so.
Generally, rubber compounds can be thought of as long, dense chains of randomly
oriented molecules, with properties subject to their degree of molecular cross linking and
entanglement. This molecular cross linking and entanglement contribute to rubbers
elasticity; hence rubbers are also referred to as elastomers (elastic polymers). The term
elastomerآ once referred to synthetic rubber compounds, it is now extended to natural
rubber as well.
The addition of certain substances to base rubber can significantly influence its response
to many factors. The use of carbon black as a filler and pigment, is widespread and well
documented, while sulphur, peroxide, acrylonitrile and many other agents are used to
enhance rubber behaviour for various end uses.
Nevertheless, only a few of the many rubber types are employed in the manufacture of
inflatable packer elements (also called glands or membranes). Choice is usually
dependent on the chemical and thermal environment that the inflatable packer element is
expected to operate within.
Typical rubber types suitable for inflatable packer elements include:
 Natural rubber (NR), such as polyisoprene which couples economy with high
strength and reasonable temperature resistance. NR is a preferred rubber for
diverse engineering applications, despite poor oil resistance and is prone to
oxidize and react with ozone.
 Nitrile Butadiene Rubber (NBR) covers a range of compounds dependent
upon the acrylonitrile (ACN) content, with higher ACN content rubbers
having greater resistance to oil. NBR offers high resilience and wear
resistance, offset by limited strength and weather resistance. A good choice
Replacement Inflatable Packers and Elements Pty Ltd
Tel: +61 08 4750700
Inflatable-packers@rripe.com.au
www.rripe.com.au

---

for temperatures up to 100C.
 Hydrogenated Nitrile Butadiene Rubber (HNBR) covers many grades based
on both the level of hydrogenation and ACN content. Overall HNBR offers
higher temperature resistance and strength than regular nitrile rubbers,
together with good abrasion and wear resistance.

Worthy of mention is the fluoroelastomer VIton ® (DuPont), which has many
excellent properties including very strong resistance to many environmental
degradants. Its use in building inflatable packer elements however, is limited
to specific applications, principally inflatable packers employed in water well
development, where statutory concerns about potential contamination of
potable water mandate its use.

Although other rubbers, such as neoprene can be used for inflatable packer
elements, NR, NBR, and HNBR rubber types under discussion are those
generally encountered.
In addition, inflatable packer elements can be mechanically strengthened by the inclusion
of reinforcing fibres such as Kevlar® (DuPont) or aircraft grade wires. The addition of
such mechanical strengthening is not universal, and depends on specific end use
applications.
It is a fact of life that rubber wears in service and deteriorates over time. As rubber is
subjected to stress/ strain and wear the inevitable changes to its resting occur, with forces
increasing with rising temperature.
Rubber performance degrades over time, even if not subjected to stress. At Replacement
Inflatable Packers and Elements we have observed some fully vulcanized rubbers
‘shrinking’ by as much as twenty two thousandths of an inch, per inch over time.
Factors influencing rubber longevity have been documented, though poorly explained
outside the industry. Such factors include oxidation, ozone attack, temperature, sunlight
ageing and out gassing. These non mechanical stressors thus affect fundamental rubber
properties resulting in loss of flexibility, abrasion resistance and elasticity due to changes
in polymer chain lengths and crosslinking.
As a result, inflatable packer vulcanite’s typically have a shelf life not exceeding ten
years, depending on both specific product characteristics and relevant ageing processes,
with actual service life being shorter than that.
Many additional factors influence the service life of inflatable packer elements, chiefly
related to down bore conditions. Bore holes are not smooth and raising and lowering an
inflatable packer subjects the rubber to abrasion. In addition, a packer element inflated to
its working pressure is subject to both extrusion and compression as the packer plugs the
bore, and long term compression set is not uncommon, particularly at high operating
pressures over time.
Replacement Inflatable Packers and Elements Pty Ltd
Tel: +61 08 4750700
Inflatable-packers@rripe.com.au
www.rripe.com.au

---

As well, dramatic rubber failure down bore can occur where a packer element inflates in
an area where the bore hole has a ‘wash out’ section, allowing part of the packer element
to out bulge excessively and rupture.
Down bore exposure to heat, oil, amines, aromatic hydrocarbons, acids, alkalis and
strongly polar fluids and gases also affect rubber life. While, as already noted, rubber
selection for inflatable packer elements is generally dependent on a rubber’s ability to
cope with hostile chemical and thermal environments (rather than mere linearity with
strain), no one rubber is completely impervious to these factors. Thus, rubber qualities are
expressed qualatively rather than quantatively, with merits in terms of ‘poor’, ‘fair’,
‘good’, ‘excellent’ and so forth.
Considering the multitude of factors affecting rubber life, it is almost impossible to
accurately predict mean time between failure of inflatable packer elements, despite rigorous
quality control, from initial rubber selection, through to the fully vulcanized product.
Inflatable packer elements have to work hard in hostile conditions.
 Replacement Inflatable Packers and Elements Pty Ltd manufactures and services
standard and custom designed OEM inflatable packers.
 We modify OEM inflatable packers to suit new or different applications and
supply associated equipment such as fittings, inflation lines and gauge boards
etc as required.
 We also offer the economic options of repairs and rebuilds of deteriorated or
damaged OEM inflatable packers.
 We pride ourselves not only on the world standard quality of our work, but also
our ongoing technical support, and fast turnaround.
 We understand that time is money and we understand inflatable packers
Replacement Inflatable Packers and Elements Pty Ltd
Tel: +61 08 4750700
Inflatable-packers@rripe.com.au
www.rripe.com.au

---

4

---

5

---