Identifying and Mitigating Pack Rust in Steel Bridges
Pack Rust Identification and Mitigation Strategies for Steel Bridges
Mark Bowman P.E. Ph.D. Chintan Patel Professor of Civil Engineering Graduate Research Assistant
School of Civil Engineering Purdue University
SPR 4121
1 Study Advisory Committee
•Timothy Wells (PA) •Stephanie J. Wagner (BO) •Christopher Wheeler •Jose Ortiz •Michael Black •Nathaniel Pfeiffer
2 3 Major Tasks
•Literature review. •Reviewing existing mitigation strategies and repair procedures for selected DOTs. •Pack rust in Indiana Bridges.
3 Task 1 Literature Review
4 Pack Rust or Crevice corrosion
•Localized attack on metal surface. •Crevice formed between two joining surfaces. • Metal – Metal • Metal – Non-metal
5 Initiation Process
• Crevice corrosion initiation process • Differential oxygen concentration needed • Aqueous solution(water), pathway for ions to flow • Process accelerated • [Cl¯] present • pH acidic present
6 Mechanism
• Formation of differential oxygen concentration cell.
Steel Specimen 7 Mechanism
8 • Inhibitors like chromium decreases the corrosion rate. • Severe corrosion takes place near the mouth of the crevice.
Crevice pH < 7 Bulk pH > 7 H+
Steel Specimen 9 Attributes of crevice corrosion •Crevice height •Ranging from 0.1 mm to 3 mm. •Large enough to allow entry of electrolyte (water) •small enough to not allow electrolyte to flow out. • Rust build-up eventually seals the crevice and the corrosion process stops. (U.R.Evans, researcher in corrosion science)
On contrary
• Sealing the crevice without neutralizing the active corrosion product can cause accelerated corrosion.(Roads and Bridges, Sept,2003)
11 Task 2
Mitigation strategies and repair procedures of selected DOTs
12 Mitigation and repair strategies •Stripe coat •Caulking •Penetrating sealer •Backer rod
13 Stripe coat
14 Caulking
15 Penetrating sealer
• Has viscosity to penetrate into the crevice. • Ability to neutralize the corrosive environment inside the crevice.
16 Backer rod and sealant
Sealant
Backer Rod
17 State Dept. of Transportation
Stripe coat (21 states) Caulking (10 states) Penetrating sealers Backer rod (5 states) (2 states) Alabama, California, California, Delaware, Washington, Oregon, Delaware, Florida, Florida, Iowa, Missouri, Iowa, Washington Georgia, Illinois, Indiana, Maryland, Missouri, Illinois, Delaware Iowa, Maryland, Ohio, Oregon, Massachusetts, Washington, West Minnesota, New Jersey, Virginia New York, North Carolina, North Dakota, Ohio, Oregon, South Dakota, Virginia, West Virginia, Wisconsin 18 Repair Procedure Oregon • Remove pack rust by mechanical cleaning, and heating water-saturated pack rust to a minimum of 250 °F and a maximum of 400 °F, or • Using 35,000 psi ultra-high pressure water jet.
19 Missouri • Calcium sulfonate rust penetrating sealer • Suitable for any steel structure that has developed pack rusting in overlapping steel plates, joints or at bolted areas. • Applied in accordance with SSPC-PA1.
20 Missouri Continued. • Can be applied to • bearings, • overlapping steel plates, • pin connections, • pin and hanger connections and • locations where • rust bleeding, • pack rust, • layered rust occurs.
21 Washington Pack rust of 1/16 inch or greater. • Clean to a depth of ½ of the gap width, maximum of ¼ inch. • Cleaned gap treated with rust penetrating sealer. • Apply Caulk to form watertight seal.
If gap greater than ¼ inch • Gap should be filled with foam backer rod material. • Apply sealant over the backer rod.
22 Task 3 Pack Rust in Indiana Bridges
23 Pack Rust in Indiana Bridges
•Gathered relevant pack rust information from Bridge inspection reports.
24 Typical Members Affected by Pack Rust •Bearings(Rocker, some cases Elastomeric) •Splice connections •Hinge-pin connection •Gusset plate and other connections •Beam cover plates •End diaphragms
25 Bearings
26 Pack Rust
27 Pack Rust
28 Pack Rust
29 30 Pack Rust
31 Splice plates
Pack rust
32 Pack rust
33 Hinge-pin connection
Pack Rust
34 Pack rust
35 Gusset plates, battens and angles
36 37 38 39 Cover plates
40 41 Diaphragms
42 Cross bracings connections
Pack Crossrust bracing fallen down
43 Statistical Analysis on Data Collected
• Total state owned steel bridges in 4 districts inspected – 1235 • No. of bridges with some form of pack rust – 422
44 Percentage of Bridges with Pack Rust 60 56 %
50
43 %
40
31 % 30
Percentage 22 %
20
10
0 Fort Wayne Crawfordsville Greenfield Seymour
45 PERCENTAGE OF BRIDGES WITH PACK RUST BASED ON FEATURE INTERSECTED Water Body Road RR Abandoned RR 75 69 61 60 63 54 48 43 39 37 33 35 26 26 28 20
FORT WAYNE CRAWFORDSVILLE GREENFIELD SEYMOUR
BERCENTAGE OF BRIDGES WITH PACK RUST OF BRIDGES WITHPACK BERCENTAGE DISTRICTS
46 MEMBER WISE COUNT Fort Wayne Crawfordsville Greenfield Seymour 94
60 50 46 42 34 36 28
NUMBER NUMBER BRIDGES OF 14 10 12 10 12 7 5 7 4 6 4 7 0 0 0 2 0 2 0 1
47 COMPARISON OF PERCENTAGE OCCURRENCE OF PACK RUST
Fort Wayne Crawfordsville Greenfield Seymour
45
29
21
19
18
17
12
8 PERCENTAGE OCCURRENCE OF PERCENTAGE
SPLICE BEARING
48 District wise Salt usage
(lane-miles) salt (tons) (tons/lane-miles)
Fort Wayne 4,652 47000 Annual10.1 Winter Maintenance Report FY 2013 by Phil Ivy
Crawfordsville 4,699 44000 9.4
Greenfield 4,500 60000 13.3
Seymour 4,693 41500 8.8
49 Splice plate pack rust in detail
50 Severity rating for pack rust in splices
Rating 1 Severe PR - > ¾ inch bowing of splices or bolt failure
51 Rating 2 Moderate to severe PR - ¼ to ¾ inch bowing of the splice plates
Rating 3 Moderate PR – Visible bowing of the splice plates < ¼ inch of PR
52 Rating 4 Minor to moderate PR - Visible corrosion @ middle of splice Connection.
Rating 5 Minor PR - Rust bleeding @ middle of splice Connection.
53 YEARS AFTER PAINTING VS. PACK RUST SEVERITY IN SPLICES (4DISTRICTS) 45
40
35 32 30
25
20
15 12
10 Number of years after painting after Number years of 5
0 0 1 2 3 4 5 6 Pack Rust Severity 54 AGE AFTER BUILT VS. PACK RUST SEVERITY IN SPLICES (4DISTRICTS) 90
80
70 56 60
50 45
40
30
20 Avg. age at pack rust detection pack rust at age Avg. 10
0 0 1 2 3 4 5 6 Pack rust severity 55 PERCENTAGE OF BRIDGES WITH PACK RUST IN SPLICES OVER FEATURE INTERSECTED DISTRICT BREAKUP
Water Roads RR Abandoned RR
25
21
17
16
15
14
13
12
11
7
7
6
6
5
PERCENTAGE BRIDGES OF PERCENTAGE
0 0
FORT WAYNE CRAWFORDSVILLE GREENFIELD SEYMORE
56 PERCENTAGE OF BRIDGES WITH PACK RUST IN SPLICES OVER FEATURE
INTERSECTED
15
10
9
7 PERCENTAGE BRIDGES OF PERCENTAGE
WATER ROADS RR ABANDONED RR FEATURE INTERSECTED
57 Trends for Cover Plates Cover plate condition vs age after painting 30
25 21 20
15 9.9 10
5 2.5 Age ofpack rust after painting after ofpack rust Age 0 minor moderate severe Condition
58 Conclusions
• Pack rust frequently occurs in Indiana bridges • Most common locations • Bearings(top and bottom) • Splice plates (joints) • Hinge-pin connections • Gusset plates • Lower chords of truss • No correlation between pack rust occurrence and salt usage.
59 Conclusions
• Common mitigation and repair methods • Stripe coat • Caulking • Penetrating sealer (Promising mitigation and repair method)
60 Future Tasks
• Investigate remaining 2 districts of Indiana. • Investigate strength degradation due to pack rust. • Review repair strategies for Indiana. Questions ?
62