DARM
MET RADIA
R
ANT HEAT
H
SHIELDS
on to Darm
met Radiantt Heat Shields
Introductio
Darchem Engineering
E
have speciialised in the
design, devvelopment and
a manufa
acture of Da
armet
Radiant He
eat Shields for
f the prote
ection of
personnel, equipment and structu
ures from ra
adiant
heat and firre.
Darchem offers two types of Heatt Shield solu
utions
based upon
n the incide
ental heat flu
ux levels an
nd the
required reduction:
•
•
Darmett Woven Me
esh System
Darmett Chevron System
S
Darmet Chevron
n System insta
alled on BP Bru
uce, UK North
ea
Se
The Darme
et Woven Mesh System
m is designe
ed for
use with low
wer level he
eat fluxes and is comm
monly
employed as
a a vertical heat shield
d protecting
g critical pla
ant, steelwork and perssonnel.
The Darme
et Chevron System
S
is designed
d
forr use with higher
h
heat flux
f
levels ssuch as thos
se
experienced during fla
aring operations.
ce of Therm
mal Radiatiion
The scienc
Thermal radiation is th
he transmisssion of heatt by the propagation off electromag
gnetic radia
ation. Unlike
e
other formss of heat tra
ansfer it doe
es not increa
ase and dec
crease linea
arly with tem
mperature but
b
proportiona
ately to the 4th power off the absolu
ute tempera
ature. The re
elationship between temperature
and therma
al radiation is
i defined by
b the relatio
onship:
q ε σ A
AT4 Radiant heaat flux is equaal to the prod
duct of emissiivity, stefan‐b
boltzmann coonstant, area and
d the fourth p
power of abso
olute temperaature ms part of th
he electroma
agnetic spe
ectrum of wh
hich visible light, radio waves and
Thermal radiation form
microwavess are also part.
p
Therma
al radiation is generally
y referred to
o as heat flu
ux and is measured in
kW/m².
In general, thermal rad
diation can be compare
ed to the be
ehaviour of visible light; in that it emanates
from a poin
nt or series of
o points an
nd dispersess in intensitty equally in
n all directio
ons. Therefo
ore, the
intensity of the heat wiill diminish as
a the dista
ance from th
he heat source increasses. This he
eat
dispersion pattern sho
ould be simp
ple to calculate given a relatively small
s
heat ssource. How
wever,
these heat sources are
e complicatted large mo
oving, three
e-dimension
nal shapes ssuch as fire
es and
flares, complicating the
e heat dispe
ersion patte
ern.
Darchem Therm
mal Protection – Darchem Engiineering Limited
d – Stillington – Stockton on Te
ees – TS21 1LB
B – UK
Tel: +44 (0) 174
40 632871 – Fa
ax: +44 (0) 1740
0 632912 – Ema
ail: dtpssales@d
darchem.co.uk –
Web: www.darcchem.co.uk
DARMET RADIANT HEAT
SHIELDS
Design of Thermal Radiant Shielding
Thermal Radiation Shielding can be divided in to two distinct categories:a) Continuous Shielding (steady state); as in the case of a flare tip on an Offshore Installation
b) Fire Hazard Shielding (limited duration); where a piece of equipment is adjacent to a potential
fire hazard for the time it would take to extinguish the potential fire.
For most design cases the same design process is used for both types of shielding and that is to
design to the worst case steady state scenario. This is because the shielding used is all metallic and
will reach steady state conditions relatively quickly.
Thermal Radiation Shielding design is substantiated by test work. It must be remembered that an
actual fire scenario is not a point source of heat and a view must be taken to the proximity of the fire
and the viewable area of the fire relative to the size of the protected item.
Darmet Heat Shield Designs
Darchem have developed two heat shield product designs:
1. The Darmet Chevron System
2. The Darmet Woven Wire Mesh System
Each heat shield manufactured is individually designed based on the incidental heat flux levels and
frequency, heat reduction target and any additional customer specific requirements. For high
incident heat flux levels the Darmet Chevron System is commonly employed where as the Woven
Wire Mesh system is employed for lower heat flux levels.
Darchem Thermal Protection – Darchem Engineering Limited – Stillington – Stockton on Tees – TS21 1LB – UK
Tel: +44 (0) 1740 632871 – Fax: +44 (0) 1740 632912 – Email: [email protected] –
Web: www.darchem.co.uk
DARM
MET RADIA
R
ANT HEAT
H
SHIELDS
oven Mesh
h System
Darmet Wo
The Darmet
D
Wov
ven Mesh syystem is de
esigned for lower
l
heat
flux le
evels. Altho
ough the sysstem can be
e employed
d as a
horizo
ontal heat shield fitted directly
d
belo
ow the flare
e tip, it is
more commonly used as a vertical
v
heat shield solu
ution
proteccting critical plant, stee
elwork and p
personnel in
n the event
of a fire, offering up to a 75%
% reduction
n in irradianc
ce.
The system
s
is ma
anufactured
d as a modu
ular system with
individ
dual panels
s made
up of a 1 or 2 lay
yers of
4 x 4 or 8 x 8 woven
mesh welded to a
chann
nel frame. Where
W
a load
d bearing
Darmet Woven
n Mesh System
m installed on the
t
require
ement is present,
Escavos Platfo
orm, Nigeria
i.e. in a horizonta
al
ating can be
e welded to the top edg
ge of the fra
ame.
system, gra
The individual panels are
a kept at a managea
able size to allow
ease of installation.
Where solid
d system ba
arriers woulld prevent natural
n
lighting
and could trap
t
gas the
e woven me
esh system has excelle
ent seethrough pro
operties and
d is naturally venting. The
T woven mesh
system also
o puts less loading from
m wind presssure on the
e
supporting structure th
han a solid barrier
b
Mo
odel showing tthe constructio
on detail of
th
he Darmet Wov
ven Mesh
hevron Sys
stem
Darmet Ch
The Darme
et Chevron system
s
wass developed
d in the
early 1980’s in collabo
oration with British Petrroleum
after experiiencing prob
blems on th
he Magnus
Offshore Pllatform. Th
he flare tip heat
h
flux was
higher than
n anticipated
d and the he
eat shield in
nstalled
was bucklin
ng and disto
orting underr normal op
perating
conditions.
As a result the underlyying steelwo
ork was being
compromised due to being
b
expossed to
temperatures beyond acceptable design con
nditions.
Following th
he Darchem
m / BP Colla
aboration th
he
Chevron syystem was developed
d
a installed on
and
the Magnuss Platform. This not on
nly resolved
d the
problem bu
ut also offere
ed a heat flux reduction of
over 90%.
Darmet Chevron
n System installed on the BP Magnus
orth Sea
Pllatform, UK No
Darchem Therm
mal Protection – Darchem Engiineering Limited
d – Stillington – Stockton on Te
ees – TS21 1LB
B – UK
Tel: +44 (0) 174
40 632871 – Fa
ax: +44 (0) 1740
0 632912 – Ema
ail: dtpssales@d
darchem.co.uk –
Web: www.darcchem.co.uk
DARMET RADIANT HEAT
SHIELDS
The Chevron system is designed, through convective airflow through the panels, to reduce the
radiant heat on the cold face of the shield to under 100oC during flaring ensuring that the structural
steelwork is not compromised.
The system is manufactured as a modular design with each
panel made up of a fabricated perimeter consisting of a metallic
edge skin with a load bearing supporting grating fixed to the top
surface ‘hot face’ of the panel. Formed thin sheet foils provide a
contoured surface to promote cold air convection up through the
panel to the ‘hot face’. The bottom surface ‘cold face’ of the
panel is supported by
expanded metal to facilitate
airflow and to hold the foil
sheets in place.
The panels are assembled
with a proprietary fixing
system, designed to allow the
system to expand during
flaring intervals while holding each panel in place to the
supporting structure.
Cross section of the Darmet Chevron
System showing the load bearing grating
and underlying contoured foils.
To allow access for maintenance, hatchways can be incorporated
in to the system, these are constructed using hinged access doors
secured with shoot bolds, welded to the cold face of the shield.
Diagram showing the cold air
convection though to the hot face of the
Darmet Chevron System
Principle Features of the Darmet Heat Shield Systems
Lightweight:
Darmet load bearing heat shields have a weight of circa 38 Kg/m2 and the
non-load bearing shields have a weight of circa 20 Kg/m2.
Cost Effective:
Darmet heat shields are competitively priced compared with solid systems.
The Darmet system can be designed and manufactured using both stainless
steel and incoloy steel.
Maintenance Free:
The Darmet system is designed to be completely maintenance free during the
projected life of the platform, even when subjected top thermal cycling from
the operational flares and extreme environmental conditions.
Heat Dissipation:
The Darmet systems have a greater heat dissipation that their solid system
counterparts. In the case of the Woven Wire System a solid plate barrier
would have a greater touch surface temperature than the woven wire system.
See-through
venting:
The Darmet Woven Wire system has excellent see-through properties and is
naturally venting. Solid systems prevent natural light and could trap gas that
may permeate from the adjacent process plant. The see-though properties
reduces the claustrophobic effect that a solid system may present during
normal operating conditions.
Darchem Thermal Protection – Darchem Engineering Limited – Stillington – Stockton on Tees – TS21 1LB – UK
Tel: +44 (0) 1740 632871 – Fax: +44 (0) 1740 632912 – Email: [email protected] –
Web: www.darchem.co.uk