1. MACHINING vs. PICKLING
HYDRAULIC PIPING STANDARDS
COPYRIGHT REDOX 2011
To easily understand standards simply look for the operative words. In every standard these
words provide clarity of action. Examples of these are: shall, will, and properly. The base stan-
dard for piping a hydraulic system is ASTM D4174 Section 9.1.1.2. It states “All pipe and tubes
shall be properly cleaned and preserved”. The words “shall be properly” require that the clean-
ing and preservation not only be appropriate and adequate but that it will also enhance every
other phase of fabrication and system operation. Additionally, this also includes the selection
and procurement of pipes and tubes that demonstrate good bending, welding and the capability to
withstand without rupture the pressures seen by the system.

2. Steel wants to attract electrons to become stable. That is what the +2 means next to Fe on the
periodic chart. This is called reduction. REDOX uses a reduction process that provides the ex-
tra electrons to stabilize the pipe in the cleaning process. Pickling removes the scale by strip-
ping away electrons. This process is called oxidation. As seen in Figure 1 this process is only
marginal at removing scale. Additionally, oxidation activates the metal and makes it very sus-
ceptible to rust. See figure 2.
The preservation of REDOX pipes uses a vapor space inhibiting (VSI) oil as called out in ASTM
D4174. This oil is hydrophobic which means it will lift water out of the grain of metal as well as
providing a continuous rust protection through emission of rust inhibiting vapors on the I.D. of
the pipe.
Pickled and oiled pipe uses a heavy AW 46 type oil that is hydrophilic which means that it will
absorb water and be a source of rust on the I.D. of the pipe. Additionally, this oil has none of
the rust fighting vapors of a VSI oil. The traces of water left in the grain of the metal will form
electrolytes with the chemical residues from the neutralization phase of pickling. The trace iron
chloride (dissolved scale) in the rinse reacts with the sodium nitrite in the neutralization tank to
form NaCl, ordinary table salt. This leads to system killing rust.
By adhering to these standards, REDOX is able to lower the cost of fabrication greater than the
total price of the pipe including shipping, while simultaneously providing more uptime profit for
the user of the system. A few of many benefits of using pipe that meets these standards are:
Corrosion free pipe
Scale resistant welding
Faster flushing
Easier to paint
Better laminar flow
Better bending
Easier handling
Better welds
Higher operating pressure capability
Reduced energy consumption
Lower maintenance cost
More uptime
All phases of piping will be explored through this series of articles. This knowledge will allow
you to not only build better systems but also to communicate effectively to win more jobs.
If you have questions…feel free to call us at 206.762.8631 or email tech@redoxinc.com. RE-
DOX has for thirty five years delivered consistent high quality products by following standards.
Feel free to quote or forward this article.