A “Toolbox” for Forensic Engineers

Fluid Transport 173
inside an enclosed system, as, for example, when steel is oxidized by dissolved
oxygen in a CHS water supply, or externally by an aggressive environment.
If dissimilar metals are used at junctions, as is common in soldering and in
many joints, then the possibility of galvanic corrosion arises. Other types of
corrosive attack will be examined in the case studies in detail, some arising
from unexpected sources. Thus when a PVC tape was used to help seal a
joint in a hot water system, thermal degradation of the PVC produced hydrochloric
acid, which attacked the adjacent metal.
6.2.3 Case Studies
The case studies in this chapter include mainly metal and polymer systems,
the former being well established for bulk transport and storage of a wide
range of fluids for many years. The case studies demonstrate the problems
that can arise in CHS systems, whether in a domestic or industrial environment.
Failed connections in oil lines can cause serious environmental problems,
and there is a study of the special problems of vehicle brake line failures.
While metal alloys remain well used and familiar to all engineers, the recurrence
of failures should act as a timely reminder of the dangers that can occur
both in new installations and older products or systems.
Plastic materials apparently offer great benefits for water supply systems
due to their great resistance to corrosion, the bugbear of steel and copper
conventional systems, but have in recent years suffered a series of failures,
especially in the U.S. There have been fewer problems with such systems in
Europe, although failures have occurred from poorly made joints, for example,
a topic discussed in detail in this chapter. Different types of failure are
examined in relation to seals in systems. They are crucial but often neglected
parts of a closed distribution network, such as in hydraulic braking systems,
where failure can have immediate and catastrophic effects on users. In CHS
networks, seal failure may be slow and undetected for some time, although
consequential damage can be severe in financial terms, as one of the case
studies demonstrates.
Flexible fuel pipes are common in vehicle engines, but once again, often
overlooked as a potential hazard, perhaps because of their low cost and
primitive function. However, if failure occurs, the results can be very serious,
resulting in loss of the vehicle or worse. The investigation into a series of
such fires in new cars in the 1970s surprisingly reappeared in the early 1990s
as a direct result of a failure to learn the lessons from first failure. Indeed,
the same kind of fuel pipe (nylon) was involved in an automobile accident
that caused several subsequent accidents due to a fuel leak. The cause lay not
so much in the nylon material, however, as in a small molded junction that
connected three pipes together.