This document contains answers to frequently asked questions about plate heat exchangers from an expert with over 40 years of experience. It addresses questions about assembly, leakage, horizontal installation, pressure spikes, reduced heat load, backflushing, certification, deformed plates, gasket types, corrosion detection, and corrosion rates for plates used in sulfuric acid applications. The expert provides concise explanations and recommendations for each topic based on his extensive expertise with plate heat exchangers.

1. 39
Heat Exchanger World July/August 2022
Plate Heat Exchangers
Q1) When I have to assemble plate packs after
service, should I use a torque wrench?
A) No, there is no need for a torque wrench. The only
criteria are measuring internal distance (A) between frame
and cover plate (see PHE’s nameplate) and tightening bolts
to the proper length (see figure 1). A common mistake is
tightening it too much, thinking that is safer, but it in fact
causes the gasket groove of the plate to be deformed and
possible leakage will occur.
Q2) In case of leakage should I remove damaged
plate?
A) Not only one plate should be removed, but a couple
every time, otherwise a mixing between two fluids will
occur. If only a couple of plates are removed, a PHE is able
to continue working without a significant difference.
NOTE: On a Plate Heat Exchanger specially designed for
high temperature duties, extreme and sudden tempera-
ture drops may sometimes cause a temporary leakage.
A typical example is a sudden shutting-off of the hot
medium flow. The heat exchanger will normally seal
Question & answer session:
Plate heat exchangers (part two)
Dr Giuseppe Tommasone has been working with Plate Heat Exchangers
(PHEs) since 1979. Over the years, he has collected commonly asked
questions about the equipment. Here you can find all of the answers
to those frequently asked questions in one place, put together over
40+ years of experience.
By Dr Giuseppe Tommasone, Heat Transfer Consultant
again, as soon as the temperatures of the equipment
have stabilized.
Q3) Due to space restrictions, I would like to
install a PHE in a horizontal position, rather than
the traditional vertical. Are there any issues
with this?
A) In principle there are no objections; maybe plates with
diagonal flow could work better than parallel flow plates,
due to no possible area for air/gas bubbles on the top,
but several studies demonstrate there are no differences
in thermal performance. Diesel engines, for example, are
typically mounted horizontally.
Q4) We have pressure spikes in our water
circuit, how can we detect if leakage is due to
water hammer?
A) A PHE responds to water hammer or hydraulic
shock in one typical way: gaskets being out of groove.
Other units like Brazed Plate Heat Exchangers (BPHE) can
experience deformation in the last plate at the end of the
plate pack due to its rigid structure. A PHE, owing to a set
of gaskets, is a little bit more flexible, but gaskets are not
able to stay in their proper position when pressure spikes
suddenly.
Q5) After weeks of operation, we notice a
significant reduction of heat load: what should
we keep under control first?
A) If flowrates are what they should be according to speci-
fications and pumps are running properly, first check on the
pressure drops. It is good practice to install pressure gauges

2. 40 Heat Exchanger World July/August 2022
Plate Heat Exchangers
upstream and downstream from the PHE. During start-up,
particles inside piping often move into the PHE which acts
as a press filter, keeping solids inside the plate pack.
Normally, pressure data is sent to OCS so the control room
is able to detect immediately any pressure drop increases.
Nowadays, IoT devices can help to read these info on
smartphones as well.
Q6) A supplier has mentioned ‘backflushing’
to increase the service period of plate pack
opening; what is this?
A) Backflushing is a system created mainly for large
seawater cooling in order to change the flow of both fluids
in the opposite direction, so that particles, debris and so on
laying on the bottom of the plate pack due to reverse flow
are dissipated.
Q7) ‘AHRI Certified’ is mentioned on a data
sheet. What does it mean?
A) The AHRI Product Performance Certification Program
is a voluntary program, administered and governed by
AHRI, which ensures that various types of heating, ven-
tilation, air conditioning, refrigeration, and water heating
products perform according to manufacturers’ published
claims. Products that are certified through the AHRI
Product Performance Certification Program are continu-
ously tested, at the direction of AHRI, by an independent
third–party laboratory, contracted by AHRI, to determine
the product’s ability to conform to one or more product
rating standards or specifications.
This program applies to production models of gasketed
plate-type heat exchangers, that utilizes any of the following
fluids on one or both circuits, for HVAC applications only.
•
Water;
•
Seawater;
•
Ethylene Glycol (10%-50% concentration);
•
Propylene Glycol (10%-50% concentration)
Q8) Our maintenance department was trying to
solve a leakage problem and tightened the plate
pack too much (less than the ‘A’ measure on the
nameplate) and the plates are now deformed. Is
there any chance to reshape the plate?
A) Generally, once a plate has lost its original corrugation
design it is not worth trying to return it to the original
shape, it is better to buy a new plate pack.
Only in the case of large plates in an exotic/expensive
material does trying to adjust the plate make sense,
bearing in mind that in any case positive results are not
guaranteed.
Q9) Several PHE manufacturers mention clip-
on, Clip-Grip gaskets, Sonderlock, Eco-Loc
glueless gaskets. Are these preferred over glued
gaskets?
(A) First of all, it’s important to understand that the
glue function of a glued gasket is to keep the gasket
in the right position for the gasket groove of the plate
and not to seal fluids. The glue is never in contact with
process fluids.
Removing the glue from the gasket it not easy (sometimes
nitrogen at a low temperature is used for easier removal).
It is common to heat up the back side of the plate with a
flame in order to remove gasket in the field, or in a Service
Centre using caustic soda at 20% at 60°C followed by
water-rinsing with water and then orthophosphoric acid
at 20%.
In the past, the main issue with glue-less gaskets was
on large plates, because once the plate pack was opened,
gaskets stuck to the back side of adjacent plate and
sometimes, during cleaning operations, they fell out of
the proper position. For this reason EPC contractors and
top players in oil gas were keeping glue gaskets in
their projects.
In recent years glue-less gaskets with better design
have been introduced, mainly in the HVAC market
and later on for industrial applications; with new
developments such as Clip-Grip, glueless gasket are
widely accepted.
Q10) We found small traces of process fluid in
the cooling water, but looking at plates we are
not able to detect any holes. What should we do?
(A) In case of chloride presence higher than 300 ppm,
corrosion (pitting) could be a possible cause with plates
made of 304/316 steel, and the small holes can be difficult
to detect.
The best way to inspect for corrosion, holes or cracks is dye
penetrant testing. Using this method, which originated in
the aviation industry, even the finest hairline cracks in the
plate can be made visible.
After cleaning, the entire surface of each single plate
is sprayed with a fluorescent paint. After the appropri-
ate exposure time, the plate is rotated and thoroughly
inspected under UV light in the darkened test room.
Damaged plates are marked accordingly and placed
aside. Flawless plates are now cleaned again by means of
high pressure.
The ultraviolet test is used upon request, usually specialty
applications where fluid mediums can only be detected
under UV light (see figure 2).
»
Figure 1 – ‘A’ distance (Source: Alfa Laval)
The A measure is the distance from the frame plate (1) to
the pressure plate (2).

3. Plate Heat Exchangers
On site dye-testing is standard for locating cracks, pin-
holes, or failures. With red dye-penetrant saturating the
plate surface, and white developer solution covering the
reverse side, this test is capable of detecting even miniscule
imperfections (see figure 3).
Q11) On data sheet, 3mm of over-thichkness for
corrosion 3 mm is mentioned. How does this
apply to a plate of 0.5 mm?
A) This is the classic result of copy paste of a Shell
Tube in Carbon Steel specification. Over thickness for
stainless steel does not occur in standard industrial ap-
plications.
The only time this would happen with a PHE is with sul-
phuric acid where Hastelloy C276 plates are used with 0.7
mm instead of 0.6 mm taking in consideration corrosion
rate of material every year.
Plate heat exchangers constructed of alloy C276 plates and
Viton gaskets impose certain limitations on the process
in order to achieve reliable and extended operation of the
heat exchangers. The maximum allowable temperature
into a plate heat exchanger is a function of acid concentra-
tion. Exceeding the maximum temperature will result in
higher corrosion rates and reduced life of the plate pack.
»
Figures 2 3 – Dye penetrant testing is carried out after cleaning to check for corrosion, holes, and even hairline cracks
(Source: AKK Industrieservice Handels GmbH)
Concentration Maximum
Temperature
Expected
Corrosion Rate
98% 90°C (200°F) 0.08 mm/year
92% 70°C (160°F) -
70% 60°C (120°F) -
About the Author
Dr. Giuseppe
Tommasone is
a heat transfer
expert and
consultant
for an EPC
contractor. His
expertise is in special heat ex-
changers in the oil gas industry
where he helps customers to im-
prove performance by providing
heat transfer solutions.
Since 1979 he has worked with
and helped more than 3000 small,
medium, and large businesses in
the oil gas, power, steelworks,
chemicals, and pharma industries
as well as EPC contractors.
Dr. Tommasone studied Chemical
Engineering in Milan, Italy.
This article is part two of a
two-part series. The first QA
session appeared in the May/
June issue of Heat Exchanger
World magazine and is
available in our online archive:
https://heat-exchanger-world.com/