Are Your Stainless Steel Surfaces
Bleach Use? Bleach is known to be corrosive to metals commonly found in pharmaceuti- cal work environments. Two commonly used types of stainless steel coupons were exposed to household bleach and sodium dichloroisocyanurate solu- tions—the rate and degree of corrosion were compared.
Jay Postlewaite, Ph.D.
Texwipe Household bleach (sodium hypochlorite solution) is used as a disinfectant in pharmaceutical, bioprocessing, and medical device facilities commonly at a 1: 10 dilution (one part bleach combined with nine parts water).
However, bleach is known to be corrosive to metals and can
cause damage to some plastics. Even with these drawbacks,
bleach is commonly used because it kills a large spectrum
of microbes, is widely available, and is easy to use. Sodium
dichloroisocyanurate (NaDCC) is a bleach alternative available
in solid tablet form. It also kills a large spectrum of microbes, is
widely available, and is easy to use.
The objective of this study is to compare the corrosion caused
by bleach and NaDCC solutions at use concentrations on two
common types of stainless steel surfaces and to demonstrate
the advantages of using NaDCC over bleach as part of a disinfection program.
For this study, 18 stainless steel 316 (316) and 18 stainless
steel 304L (304L) 2” x 2” x 1/8” coupons were obtained from
GlobePharma. Six solutions were prepared daily with deionized water ( 18 MΩ RODI) using commercially available
Clorox® bleach and commercially available tablets containing
NaDCC. The solution concentrations, formulations, and
appearance are compiled in Table 1.
Three coupons were submerged in 400-mL beakers con-
taining 250 milliliters of one solution listed above ensuring
complete coverage of the coupons. The beakers were then
covered with plastic wrap. The coupons were removed from
the beakers daily and wiped dry for visual inspection. Any
differences were documented and photographed, as noted in
Figures 1-3. Noted differences include changes in color, rust
and corrosion, pitting, gas evolution observed while sub-
merged in solution, and metal deposition on the glass surface
of the beaker.
After inspection, fresh solutions were prepared for each
coupon-solution combination, and the coupons were placed
back in their original beakers. The beakers were maintained
in an ISO Class 7 environment. The study was conducted
over eight weeks. However, the undiluted bleach samples were
maintained an additional four weeks until metal was deposited
on the glass beakers.
After four days, the 304L coupons in the 1: 10 bleach solution
exhibited definite corrosion as shown in Figure 1. The 316
coupons in the 1: 10 bleach solution also exhibited corrosion,
but to a lesser extent. Pitting began in the first week for both
304L and 316 coupons in the same solution. After one week,
the 1: 10 bleach solution containing the 304L coupon was
brown from rust floating in the solution. The 1: 10 bleach
solution containing the 316 coupons was gray. In contrast, the
1,000-ppm NaDCC solutions containing the 316 and 304L
coupons remained clear.
By eleven days, the glass beaker sides containing the 304L
coupon in the 1: 10 bleach solution were contaminated with
rust. At two weeks, there was pitting, corrosion, and staining
of both 304L and 316 1: 10 bleach solutions and full-strength
bleach solutions. The 304L and 316 coupons were clean in the
water, 200 ppm, and 1,000 ppm NaDCC solutions (Figure 2).
At three weeks, the 1: 10 bleach solution containing the
304L coupons was colored black. Corrosion began to appear
on one 304L coupon in the 1: 50 bleach solution. By four
weeks, the 304L coupons in undiluted bleach were evolving
a gas as evidenced by bubbles rising in the solution from the
coupon edges and faces, and, between observations (one time),
rust was splattered on the plastic wrap beaker cover. At six
weeks, metal deposition began on the glass beaker wall for the
1: 10 bleach solutions containing the 304L and 316 coupons.
Solution Formulation Appearance
Deionized water Undiluted Clear
Household bleach Undiluted Slight yellow
Household bleach diluted 1: 10 25 mL bleach, 225 mL
Household bleach diluted 1: 50 5 mL bleach, 245 mL
NaDCC 937 ppm (nominal 1,000 ppm) 1 tablet diluted in 1 gal
NaDCC 187 ppm (nominal 200 ppm) 50 mL 1000 ppm solu-
tion, 200 mL water
Table 1. Test solution
formulations used in
the corrosion study.