The document discusses guidelines for maximizing the lifespan of fabric penetration seals used in heat recovery steam generator (HRSG) applications. Modern fabric penetration seals offer a gas-tight alternative to traditional metal bellows. Key factors that influence the longevity of fabric seals include: 1) Ensuring professional installation by experienced crews, as improper installation can lead to rapid failure despite high-quality materials and design. 2) Engineering the seals specifically for the movements and conditions at each piping penetration by verifying dimensions on site before installation. 3) Creating an environment for success by identifying and addressing hot spots, insulating pipes properly to prevent excess heat, and allowing ventilation across the seal.

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FLUID SEALING SPECIAL ADVERTISING SECTION
Maximizing the life of fabric penetration seals
Matt Long of EagleBurgmann Expansion Joint Solutions explains how best to use modern
gas-tight fabric expansion joints for heat recovery steam generators (HRSGs)
Heat recovery steam generator (HRSG) pipe
penetrations are an aggressive and diffi-
cult location to seal exhaust gas (Figure 1). As
designs and materials have improved, last de-
cade’s “rag joints” are now highly engineered
gas-tight solutions, and sites are relying on
fabric penetration seals more often to ensure
safe and reliable operation.
Metal and fabric expansion joints at a
piping penetration are referred to as “pen
seals”. Modern fabric pen seals are con-
structed with layers of high-temperature
fiberglass cloth, insulation, and a gas bar-
rier. The flexibility these components offer
is ideal when accommodating the axial
and lateral movements seen in boiler pipes
throughout an HRSG.
In HRSG applications, piping penetra-
tions create a unique set of challenges to
overcome: intense heat, large movements,
and limited space for installation and op-
eration. Fabric penetration seals offer a
gas-tight alternative to slider seals, and
can be a cost-effective solution to replace
metal bellows. Any O&M project should be
given the best chance to succeed, and these
guidelines will help achieve longevity from
a fabric penetration seal installation.
Professional installation
Even the greatest designs and advanced
materials can be negated by an improper
installation; an inexperienced crew can
lead to rapid failure and forced downtime.
Operating conditions and movements are
different at every site, even amongst the
same manufacturers, so experience cannot
be overlooked when identifying potential is-
sues during installation. Choosing a suppli-
er with professional and experienced crews
will provide an immediate payback, and is
the surest way to protect your investment.
Fabric seals should be engineered for
the exact movements and conditions at
each piping penetration, and movements
should be verified in the field before instal-
lation. OEM as-built drawings are the best
resource for proper design, but don’t al-
ways represent the current operating condi-
tions and changes to the surrounding area.
Penetration seals should therefore be built-
up on site and installed after verification of
dimensions and movements.
Create an environment for success
Before installation, proactively identify and
fix problem areas around the penetration
that can contribute to early failure.
Identify hot spots on the HRSG casing
where paint is missing, repair liner plates,
and replace missing insulation. Locate other
external sources for “heat attacks”: these
include leaking slider seals or drains with
failing bellows.
The expansion joint must be able to
breathe and reject heat to maintain a cool
outer surface and protect the gas-tight
barrier. Insulators and expansion joint in-
stallers should work together to properly in-
sulate pipes and headers to prevent excess
heat on the fabric seal.
Similar to other fabric expansion joints,
never insulate over the flanges, clamping
bands, or outer cover. Insulation cladding
should be tapered to the pipe attachment
flange, providing a safe operating envi-
ronment without directing heat onto the
expansion joint (Figure 2). The surround-
ing structures should allow for ventilation
across the module to lower the ambient
temperature, and prevent radiation from the
HRSG casing to the seal (Figures 3 and 4).
Plan ahead
Allowing for inspection before the out-
age will result in a proper design for each
unique penetration. Fabric expansion joints
are highly engineered, custom products;
but not all fabric penetration seals are
equal. Plant owners should partner with an
FSA member company with experience and
expertise, and review references from simi-
lar installations to ensure the best return on
investment. ■
Figure 2: Avoid directing heat onto the
expansion joint by tapering insulation
to the pipe attachment flange
Figure 3: Before replacement
of fabric penetration seals
Figure 4: After installation of gas-
tight fabric penetration seals
Figure 1: Intense heat, large movements,
and limited space create difficult design
challenges for HRSG pipe penetrations