Stop the rot
Corrosion strategies need to strike a balance between cost and common sense, explains Iain MacIntyre
Despite significant ongoing advancement in operational technologies being developed for ports, the inherent volume and prevalence of sea water/salt spray in such environments continues to present a fundamental corrosion threat to equipment.
Given it is not economically or operationally feasible to transition to materials that do not corrode in most situations, port executives need to appropriately identify and analyse an evolving range of variables in order to develop an optimal corrosion control strategy.
Such is the advice of Washington DC-based published author of numerous civil engineering papers, Carl Magnell, who observes that stakeholders can mistakenly focus on straightforward cost as their major strategy-determining criterion.
“Cost has many dimensions and ironically, the least significant cost component can/may turn out to be the initial procurement cost of the technology solution itself.
“Why is this so? Simply because the cost of corrosion protection has many facets, including labour, equipment/port downtime, management/employee buy-in, safety and liability considerations, other operational impacts and even, goodwill.
“A seaport corrosion prevention strategy should therefore encompass all cost parameters, both the actual (tangible) and the opportunity costs that result from corrosion impacts. And, importantly, analysis is required to identify items to be protected and their relative priorities.”
Mr Magnell advises the following major inputs should be considered in developing an effective corrosion strategy: management buy-in; employee buy-in; equipment maintenance status; employee training level; labour cost; safety awareness; liability impact; cost of corrosion products; product effectiveness; time value; goodwill impact; and corrosion ‘master list’.
“These inputs are really just common sense factors … however, some are more significant than others. For example, if management buy-in is low it is likely that an effective strategy is beyond achievement since, as a consequence, employee buy-in is unlikely as is adequate resourcing.
“On the other hand, all the buy-in that can be generated from management and employees can’t substitute for an ineffective corrosion mitigation technology/product. Moreover, there are trade-offs between factors that should be carefully considered in formulating and executing a strategy.”
Mr Magnell warns of the potential to overlook critical components when compiling a master list of items to be protected from corrosion. He cites one particular case of a simple control switch that was rendered unable to perform its intended purpose after being subjected to 100 hours of salt spray. With adequate protection, such a switch was then able to operate for 1400 hours while exposed to the same conditions.
“It exemplifies the need to think outside the box when treating corrosion and identifying where corrosion protection is needed. It also suggests that there are some items that must be given priority in an effective corrosion strategy -- ie, inspected more frequently and treated with the best possible technology solution(s).”
Furthermore, Mr Magnell cites another experience with corroding sump pumps at a US fuel dispensing station - lessons learned from which he says could just as easily be applied to any equipment or infrastructure found in a seaport.
“The accepted solution appeared to have been to let corrosion occur until system failure or warnings/shutdown by regulatory authorities - with obvious impact on operations and goodwill to name only two corrosion strategy factors - and an apparent focus on applying minimal corrective action at lowest perceived cost.”
Aware that extensive corrosion was returning four months after each episode of scraping and painting, significant efforts were made to convince management of the value of implementing a more expensive technology combination.
“After scraping, brushing and removing surface rust, a rust converter was applied to all substrates. After painting the metal substrates, the actual corrosion prevention treatment was applied using a Milwaukee sprayer to ensure adequate penetration of the smallest cracks and crevices.”
With the treated sump pumps still looking pristine four months after treatment, Mr Magnell says the new technology solution implemented fully demonstrated the “importance of considering tradeoffs”.
“It is evident that, in this case, an effective corrosion strategy was not initially in place and both management buy-in and initial product cost factors were among the impediments preventing this.”
Providing an equipment manufacturer’s viewpoint, Liebherr Container Cranes sales and marketing representative Trevor O’Donoghue says his firm’s range of container cranes are generally supplied after an extensive tendering process during which surface protection is specified.
“For example, the ISO Standard 12944 details such surface protection and specifies corrosion protection of steel structures by protective paint systems,” he says.
“Protection against corrosion for non-painted components can be specified by further standards and codes, for instance, protection against water ingress is specified by the IP Code. Components such as hoist motors, electrical drive systems are enclosed in weather-proof machinery and electrical houses.”
In addition to the experience gained from having supplied container cranes to the port sector since the 1960s, Liebherr’s customers also benefit from a recommended maintenance schedule issued with its equipment and the offer of lifetime service support, adds Mr O’Donoghue.
“Liebherr container cranes are designed for, and are well known for, their exceptional long lifetime in the port environment. For example, a Liebherr ship-to-shore container crane supplied to Nicaragua in 1978 is still in service today - more than 35 years later.”
Commenting specifically on the mobile harbour crane sector (MHC), Liebherr Middle East MCCTec sales division manager Gordon Clark says corrosion control of this equipment is largely predicated on paint finish.
“We use the same paint finish on the MHC as we use on our offshore and ship cranes, meaning the standard is far higher than most port requirements,” he says.
“Internal surfaces have a dry film paint thickness of minimum 185 microns, whilst external surfaces have 250 microns. The paint system employed is a two-pack zinc epoxy primer, sprayed on to metal shot-blasted to SA 2.5 to get best adhesion. A two-pack intermediate coat of Micaceous Iron is then applied and final a colour coat of Siloxan.
“The thin-walled slewing platform uses GRP [glass reinforced plastic] structure. Thin metals cannot easily be blasted to SA 2.5 as they deform and therefore the GRP is used.”
Mr Clark emphasises that Liebherr’s maintenance manuals also instruct customers where diligence is required.
“Hydraulic cylinders for example, which should be lightly oiled periodically. Depending on the port and application, more or less corrosion protection will be needed. For example, in hot, humid temperatures, with high saline atmosphere, corrosion will be at its worst.”
He adds that some bulk products - fertiliser being a prime example - can be particularly aggressive to metals and must be regularly washed off MHCs.
“In applications such as this we also offer other options to protect the machine: dust covers and bellows over-pressure within enclosures to keep product out, additional protection to hydraulic lines using denso-tape etc.”
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