May 1949
Corrosion Environment and corrosion testing of small pieces of equipment in the pilot plant are described by Mars G. Fontana
P
REPARATION and identification of specimens, .their location and support, and time and temperature factors in connection with pilot plant corrosion testing were discussed in March and April. This column concludes this series of three articles. In general, these discussions also apply to actual plant or field tests. A factor which must be considered most carefully in corrosion testing is the environment or the corroding medium. Needless to say, unreliable and often worthless results can be obtained if the tests are made in an environment that is essentially different from contemplated actual conditions. This is one of the important reasons why pilot plant testing is extremely desirable and valu able. In most cases, commercial materials and not e.p. reagents are handled in the pilot plant. It is a well known fact that minor, and so-called unknown, impurities often change completely the corrosion picture or the life of equipment. An excellent example concerns hydrochloric and muriatic acids. This acid is quite corrosive and small amounts of impuri ties often increase the severity of corrosion, c.p. hydrochloric acid is somewhat different from ordinary commercial muriatic acid. The problem is further complicated by the increasing use of recovered or by-product hydrochloric acids in the chemical and petroleum industries. In many instances, these acids contain appreciable amounts of iron which means that they often contain ferric chloride. This iron is picked up in the plant operations be cause of corrosion in the process. Ferric chloride is one of the
most destructive pitting agents known. Cupric chloride is another bad actor in this respect. The corrosion picture could change also, in the other direction, how ever, in that sometimes these recovered acids contain organic matter which may act as an inhibitor and actually decrease the aggressiveness of the acid. In some cases, the compositions of the fluids handled are confidential in nature and outside help and vendors of equipment cannot be furnished this information. This situation is remedied iti the pilot plant in that the actual fluids are handled. The pilot plant tests also take care of other factors such as changes in the chemical and physical nature of the environment during operation; intermittent changes in environment, which are often encountered in batch operation; relations between the vol ume of liquid handled and surface area of the equipment; vibra tion; velocity effects ; catalysis effects; pressures; and tempera ture fluctuations. This latter item is generally overlooked, but in several cases of severe and disastrous stress-corrosion failure, in vestigated by the writer, the primary cause of failure was the very high stresses induced in the metal because of severe thermal gradients. Stresses of the order of 50,000 pounds per square inch were involved. This factor is so important that the author is planning an investigation, {Continued on page 96 A)
NO A I R LEAKAGE t h r u stuffing b o x into v a c u u m
For h a n d l i n g c h e m i c a l s o l u t i o n s , T a b e r Pumps are e q u i p p e d w i t h a d r i p chamber a n d c o v e r . W h e n in v a c u u m service on evaporators, the w a t e r - f i l l e d d r i p chamber prevents air f r o m entering thru the pack i n g . This water-sealing of the stuffing box is absolutely d e p e n d a b l e .
ROLLER MILLS . . . by Sprout-Waldron
Taber Single Suction Centrifugal Pumps are
Sprout-Waldron Roller Mills are in use on mate rials ranging from hard flinty slate to soft spongy cork. By varying roll corrugations and differen tials, you can reduce to FLOUR fineness, GRAN ULAR or F L A K E form as desired·. Consider a S-W System based on stage reduction . by rolls. Write for details.
as a d a p t a b l e as they are efficient. For complete i n f o r m a t i o n , please w r i t e on your l e t t e r h e a d for
TABER SPECIAL BULLETIN
CL-339
TABER PUMP CO. · Est. 1859 · 293 ELM ST., BUFFALO 3, Ν . Υ.
TABER
Higher. Practical Performance
SPROUT-WALDRON & COMPANY
PUMPS
Manufacturing
10 WALDRON STREET 95 A
Engineers
MUNCY,
PA.
