|
1. STRIPPER
RUBBER PACKER INSERTS
a) MATERIAL NOTES
1.1 Original Systems
| 1.1.1 |
3100 Series:
Delisted. Polyurethane 90A rated to 100C/212F; shown by
testing to withstand 120C/250F for a few hours. De-listed in view of the
improved products below; it is false economy to use old versions and
rediscover old problems. This range was technically equivalent to
standard products from Bowen, Chimo or TOT.
|
| 1.1.2 |
3200 Series:
Delisted. Polyurethane 75A rated to 100C/212F; energises easily,
but softens at higher temperature rather more
readily than 90A. The 3500's are to be preferred.
|
| 1.1.3 |
3160 Series:
Silicone 60A rated to 300C/575F, but very much lower wear
resistance; these have been used successfully on a few high
temperature geothermal wells. They may occasionally still be
called for in exceptional circumstances, but in most cases the
HT/HP forms are preferred. No longer listed; available on request.
|
| 1.1.4 |
3400
Series: Delisted. The first new upgraded standard insert,
tested and approved against many others in an engineering
research project. Based on 95A hard material, in red, it was recommended
for T > 100degC/212F and P > 3500psi, but in this it is now overlapped
by the 3700 series, which is now supplied, having been tested
subsequently to greater extremes. |
|
1.2 Current systems |
|
Upgraded standards offer better wear characteristics and reliability. They
have a built-in self-lubrication which reduces frictional wear and
start-up jamming. They also have much better tolerance
at both low (-50C/-60F) and high (+160C/320F) temperatures. They do not
embrittle at the upper limit so that even at excessive temperatures
they do not precipitate a catastrophic breakdown.
They also do not show any explosive decompression damage at high pressure.
These properties are proving so advantageous that the products have
gained wide acceptance.
|
| 1.2.1 |
The 3500
series is based on a 75A hard, but otherwise identical, form of
the same
material used in the 3400 series above and is easier to
energise at LT/LP. The
general guideline is that these are to be used usually
when T < 80degC/175F and P < 2500psi. These are being steadily replaced
by 3800 series. |
| 1.2.2 |
The 3600
series has improved wear and temperature resistance and replaces
others for standard use, including our 3100 series. It is based on
a 90A rubber with crosslinking and self-lubrication. For
extreme pressures and temperatures, use the 3700 series.
It is recommended for 80C/175F < T < 150C/300F and 2000 < P <
4000psi.
|
| 1.2.3 |
The 3700
series has extra wear and temperature resistance due to the
harder form of the polymer as well as the polymer type and built in
lubricating agent. It is for application at extreme pressures and/or
temperatures (>4500psi, >125C/260F) instead of the 3600 series.
They are not to be expected to be without wear if pushed to say
10,000psi or 160C/320F, but they will wear uniformly, ie safely,
if evenly loaded. Because they show no tendency to brittle fracture or
explosive decompression, this enables them to be run with confidence.
They are, however, designed to be the wearing part of the system and
should be checked often when used at extremes. They should always
be changed between runs; anything less is a false economy in a high
pressure environment.
Though suitable for any operation when T > 100C/212F and P >
3500psi, it becomes essential for T > 120C/250F and P > 5500psi. |
|
| 1.2.4 |
A 3800
series has been recently introduced. It is based on a softer
rubber (80A) than the 3600 series but, like that series, includes a
self-lubricating agent and is cross-linked. It therefore wears
rather better than the 3200 and 3500 series. It is expected to
serve those applications of low pressure and low temperature where it
is desirable that the rubbers be relatively easy to energise. This
means that it is believed suitable in VLT use (-50C/-60F) and at the
same time serves a higher temperature (+120C/250F) than equivalents of
the 3500 series; comment on experience is welcome.
|
| 1.2.5 |
A further series
for VHT use is now being offered, based on a quite different material.
Aflas (TM Asahi) is capable of withstanding 200C/400F. Please enquire
for particular sizes.
|
|
b) DESIGN NOTES |
|
1. Sealing Face |
|
We have considered the alternatives to flat sealing faces, which
have been promoted (by
other suppliers) as giving a more positive seal, evaluating
various wavy and toothed
interlocks. Although there is an apparent case for supposing
that interlock produces a more
ready seal, there appear in tests to be no actual sealing
benefits over an equivalent size of
flat face seal. Also, although the interlock may reduce the
chance of ejection of one half
when bad wear occurs, we find that a good material will not wear
to give this problem
anyway. It also appeared that once wear started in an interlock
system, it was actually
worse on the area near the join. We therefore do not at present
list or intend to list such
varieties though some might be made available on request. |
|
2. End Face |
|
A further modification has been incorporated into some stripper
rubbers; this consists of
reinforcing the end faces in order to try to reduce the tendency
to wear excessively, which
sometimes takes place at the ends causing a funnel shape. We
find that a marginal life
improvement may indeed be obtained with the standard materials
where these are incorrectly
used, but that correctly selected and used materials perform well
without need of any
reinforcement. Also, at elevated temperatures, combination
materials have been known to
spall apart; the bonding between different materials introduces a
complication to the product.
As with sealing faces above, we do not at present list a range,
but they can be made
available.
Feedback on use of rubbers in stuffing boxes is always welcome
and any suggestions for
improvement will be carefully considered.
|
c) IDENTIFICATION
|
Stock is individually labelled and marked with a part number and
a batch date. We
previously bagged products individually in black plastic as a
protection against degradation
by air, moisture, heat and light. However, we have also been
studying the behaviour of
polyurethane products not so protected and have shown that there
is no noticeable change of
condition over ten years. We therefore decided to discontinue
the bagging of packer inserts,
with the benefit that products are identifiable at sight.
In the lists, all packers are described with ID / OD / L on OD.
The ID corresponds to
the CT diameter, and the choice of OD & L depends on the stuffing
box to be used. We
have sometimes been asked for a comparision of part numbers with
competitor products; this
is not directly possible, since to state for example that our P/N
1234 was the equivalent of
Bowen's 98765 or TOT's 43210 would be inexact. Materials and
construction differ, so that
exact parallels are unlikely to exist. What matters is the fit
in the stuffing box and the
functionality of the materials. The differing material
performances as tested have been
indicated above which is why we offer choices of material.
Not all options are equally recommendable. Thus, a Bowen 4.625
box can be fitted with its
4.625 OD x 3.00 ID energiser and replaceable 3.00 OD rubbers, but
it is as well fitted by
our 4.625 OD series all-in-one rubbers, which offer the safety
benefit of reduced leak paths;
Bowen opted for the same design in their second series - our 3679
et seq. The same is true
of a TOT 5.50 OD box, where we offer not only the energiser plus
4" OD inserts, but,
particularly for the larger CT sizes, all-in-one sets of rubbers.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
This website was authored by the IT Manager, Benoil.
All pages of this site are © 2008 Benoil Services Ltd.
|
|
