Fuel tanks / DEF tanks
DESCRIPTION OF TECHNICAL CHALLENGE
Cost pressure in the automobile and supply industries is high. At the same time, the need toreduce emissions is increasing. For example, in the US fuel tanks have to fulfill the requirementsof the Low-Emission Vehicle Program - LEV III. Another example is the introduction of theSelective Catalytic Reduction (SCR) technology and the Diesel Exhaust Fluid (DEF) tanks usedfor this technology. To remain competitive, production and delivery processes must always beoptimized.

The need to reduce emissions resultsin stringent leak rate requirements forfuel tanks.

Automotive fuel tanks are constructed of two materials, metal and plastic. Plastic fuel tanks, asused for passenger vehicles as well as heavy trucks and off-road equipment, typically consist ofHigh Density Polyethylene (HDPE). Metal fuel tanks are comprised of either steel or aluminum.
Fuel tanks for two-wheelers are usually made from metal, however, the recent trend of lightweightmaterials has started its penetration into this segment and is projected to grow significantly overthe next five years. Plastic fuel tanks usually have higher requirements for leak testing than metaltanks. Typical leak rate requirements for fuel tanks are in the 10-4 .. 10-6 mbar·l/s range. DEFtanks are usually made from polyethylene materials as well. Leak rate requirements for DEF tanks
are in the 10-4 mbar·l/s range.
Fuel tanks are often tested in a water bath and sometimes supported by ultrasonic detection ofbubbles. However, water bath testing of fuel tanks poses a significant challenge. First, plastic fueltanks are designed to withstand pressurization to only a few hundred mbar above atmosphericpressure, so the internal pressure that may generate the bubbles is low. In addition, when pushinga fuel tank under water, significant forces apply to the fuel tanks due to its buoyancy caused by
the enclosed air. For fuel tank testing in water bath, the fuel tanks usually need to be placed in a
supporting cage before being dumped into water. These cages need to be customized to eachfuel tank design to offer the best mechanical support. Once the fuel tank has been pushed underwater, large amounts of turbulence in the water (bubbles) must clear so conditions can stabilize
and bubbles from real leaks can be detected with confidence.
In general, water bath testing is only suited for leak rates down to 10-4 mbar l/s at its absolute
minimum. It is incapable of finding the smaller leak rate ranges. With increasing requirements forlow emissions, the applicability of water bath testing will further degrade.

THE INFICON SOLUTION
Depending on the size of the tank and the required throughput, two tracer gas solutions areavailable today:
Accumulation method

Vacuum leak testingThroughput

Low to medium

Medium to high

Fuel tank size

SmallMedium to large

LEAK TESTING OF COMPONENTS
FUEL TANKS

For medium to large tanks (cars and trucks) that need
to be tested with medium to high throughput, leaktesting with helium in a vacuum chamber isrecommended. For this testing process, the tank isplaced in the testing chamber and connected to thevacuum system. Once the chamber lid is closed, large
vacuum pumps pull a vacuum on the inner volume of
the tank as well as on the vacuum chamber. The partand chamber are evacuated simultaneously to avoid
too high a pressure load on the tank (this usually does
not exceed 200… 300 mbar / 3-4 psi). Subsequently,
the part is backfilled with low amounts of helium(again do not exceed the maximum pressure load of
Medium to large tanks can be tested with highthe tank). Helium then has the opportunity to migrate
throughput by helium vacuum chamber systems.
outwards and if a leak is present, the INFICONLDS3000 Helium Leak Detector (connected to the vacuum chamber) detects the helium atoms
as they emerge from the tank.

For small fuel tanks (motorcycle) or smaller DEF tanks that need to be tested with
low to medium throughput, leak detection with helium or hydrogen in an
accumulating chamber under normal pressure (accumulation method) provides an
economical solution

For small fuel tanks or smaller DEF tanks, leakdetection in an accumulation chamber offers an
economical solution.

In a simple chamber, the tank is filled with small amounts of helium or hydrogenthrough its test gas connection. As the tanks cannot be evacuated in thesurrounding atmospheric pressure (maximum allowable pressure load of the tank isusually only 200… 300 mbar / 3-4 psi), the tank will be filled by pumping through,sucking out air on one side and backfilling with helium from the other side, toensure filling with close to 100% helium concentration. After filling, the test gas will
escape through any leaks into the accumulation chamber. Fans ensure an even
distribution of the test gas in the chamber – so, independent of the position of theleak, precise measurement values are guaranteed. The T-Guard Helium sensor
then determines the test gas content in this atmosphere and calculates the leak rateof the part from this value.

BENEFITS OF LEAK TESTING WITH TRACER GAS•••••

Accurate and repeatable measurements for confident leak testing
Test result independent of operator intervention
Also able to detect smaller leaks (10-4 .. .10-6 mbar l/s range)
Dry, non-corrosive process
High throughput

For more information, please visit us atwww.inficonautomotive.com

w w w . i nf i c o n. c o m

re a c hus @ i nf i co n. c o m

Due to our continuing program of product improvements, specifications are subject to change without notice.
miaf00en-b (1604)©2016 INFICON