izamil
Mechanical
- May 1, 2002
- 30
I am encountering a small problem with hot dipped galvanized stair treads that have started to accumulate rust and in some locations corroded to the point of pitting.
The hot dipped galvanized stair treads are bolted to spiral carbon steel stringers on a large diameter carbon steel tank in a power plant. The power plant is at the seashore.
I (the manufacturer) of the stair treads have fabricated them out of carbon steel ASTM A36, grit blasted them, then brought them to the hot dip galvanizers to galvanize in accordance to ASTM A 123.
The contractual requirements are for me to perform the above for which I have done so, and even have witnessed signed certification stating that the galvanized coating is in accordance with ASTM A 123.
When the erector (a different company appointed by the client) bolted the stair treads (in their newly galvanized condition) to the carbon steel (bare metal) stringers, he started blasting the stair stringers with garnet (a blasting media) and coated them with inorganic zinc rich primer.
As the rust formations started only at the nosing of the stair treads, we are alleging that while blasting the stringers with garnet, the thrust of garnet spray tremendously thinned the nosing area if not removed at locations the zinc completely which accelerated the corrosion.
The erector on the other hand, (who is trying to pin all the problems on my company) is stating that the main cause of rusting (zinc salt/white rust) is mainly from the environment conditions. He states that the very corrosive environment in coastal areas has deposited a lot of chloride, and dust particles through heavy winds and high humidity, chloride has contaminated the hot dipped galvanized surfaces, which have now started converting into brown rust.
I have pictures illustrating also at locations where the erector has actually tack welded and bolted the stair treads to the stringers.
The questions are:
1. Can I prove by means of technical matters that the blasting media started the corrosion by removing the ZINC?
2. How true is this zinc salt/white rust phenomenon? Could such phenomenon lead to such pitting? Is there a scientific explanation that assists me in getting the erector off my back?
I am sorry if this whole thing is a little too long, but I would appreciate as much help as possible,
Respects,
p.s. I do not know how to post the pictures on here.
The hot dipped galvanized stair treads are bolted to spiral carbon steel stringers on a large diameter carbon steel tank in a power plant. The power plant is at the seashore.
I (the manufacturer) of the stair treads have fabricated them out of carbon steel ASTM A36, grit blasted them, then brought them to the hot dip galvanizers to galvanize in accordance to ASTM A 123.
The contractual requirements are for me to perform the above for which I have done so, and even have witnessed signed certification stating that the galvanized coating is in accordance with ASTM A 123.
When the erector (a different company appointed by the client) bolted the stair treads (in their newly galvanized condition) to the carbon steel (bare metal) stringers, he started blasting the stair stringers with garnet (a blasting media) and coated them with inorganic zinc rich primer.
As the rust formations started only at the nosing of the stair treads, we are alleging that while blasting the stringers with garnet, the thrust of garnet spray tremendously thinned the nosing area if not removed at locations the zinc completely which accelerated the corrosion.
The erector on the other hand, (who is trying to pin all the problems on my company) is stating that the main cause of rusting (zinc salt/white rust) is mainly from the environment conditions. He states that the very corrosive environment in coastal areas has deposited a lot of chloride, and dust particles through heavy winds and high humidity, chloride has contaminated the hot dipped galvanized surfaces, which have now started converting into brown rust.
I have pictures illustrating also at locations where the erector has actually tack welded and bolted the stair treads to the stringers.
The questions are:
1. Can I prove by means of technical matters that the blasting media started the corrosion by removing the ZINC?
2. How true is this zinc salt/white rust phenomenon? Could such phenomenon lead to such pitting? Is there a scientific explanation that assists me in getting the erector off my back?
I am sorry if this whole thing is a little too long, but I would appreciate as much help as possible,
Respects,
p.s. I do not know how to post the pictures on here.
