Page 177 - Machinery Component Maintenance

Process Muchinery Piping 159

3. Place pipe in an acid pickling bath. Use a 5 to 12 percent solution
of hydrochloric (muriatic) acid, depending upon the condition of
the pipe. Rodine inhibitor should be added to the solution to pre-
vent the piping from rusting quickly after removal from the acid
bath. The temperature of the bath should be 140-165°F. The time
required in the acid bath to remove scale and rust will vary, de-
pending on the solution strength and condition of piping; however,
six hours should be a minimum. The normal time required is about
12 to 14 hours.
4. Remove pipe from acid bath and immediately wash with cold wa-
ter to remove all traces of acid.
5. Without allowing piping to dry, immerse in a hot neutral solution.
A one to two ounce soda ash per gallon of water solution may be
used to maintain a pH of 9 or above. The temperature of the solu-
tion should be 160 to 170°F. Litmus paper may be used to check
the wet piping surface to determine that an acidic condition does
not exist. If acidic, then repeat neutral solution treatment.
6. Rinse pipe with cold water, drain thoroughly and blow out with hot
air until dry.
7. Immediate steps must be taken to prevent rusting, even if piping
will be placed in service shortly. Generally, a dip or spray coating
of light water displacement mineral oil will suffice; however, if
piping is to be placed in outdoor storage for more than several
weeks, a hard-coating water displacement type rust preventative
should be applied.
8. Unless piping is going to be placed in service immediately, suit-
able gasketed closures must be placed on the ends of the piping
and all openings to prevent entrance of moisture or dirt. Use of
steel plate discs and thick gaskets is recommended for all flanges.
Before applying closures, the flange surfaces should be coated
with grease.
9. Before installation, check that no dirt or foreign matter has en-
tered piping and that rusting has not occurred. If in good condi-
tion, then pull through a swab saturated with carbon tetrachloride.
IO. For nonlubricated (NL) units where oil coaling inside piping is not
permissible (due to process contamination), even for the starting
period, consideration should be given to one of the following al-
ternatives:

(a) Use of nonferrous piping materials, such as aluminum.
(b) Application of a plastic composition or other suitable coating af-
ter pickling to prevent rusting.