Corrosion Control During Layup

Garry Best Practises

Corrosion Control & Environment

High humidity is a problem whether you are looking to lay up in Africa or Asia. Look for the signs and understand and plan and prepare for lay-up.

Most companies are trying to balance cost efficiency with lay-up effectiveness with differing results. Part of the problem is the climate. Therefore it should be understood to see what the impact may be.

Consider the following.

Providing a Good Lay-up Solution Involves

  1. Corrosion control
  2. Eliminate seizure of equipment
  3. Understand failure modes
  4. Mitigate where possible
  5. or Reduce the impact

Classification & insurance companies provide recommendations on what needs to be considered as part of lay-up. Dehumidification & preservation are the two techniques most preferred. Classification societies recommend dehumidification as the preferred primary solution to eliminating corrosion & good paintwork as the preferred preservation solution where necessary.

As such, this article discusses item 1 above, corrosion control.

Corrosion Control

Understanding what lay-up is all about, how to be cost efficient and lay-up effective and when & where to use each solution is paramount in getting the best value for money.

Lay-up Solution Management

The following triangle figure 1 is an Engineering Hierarchy of Control where the most effective solution is eliminating the problem before it occurs. Therefore if humidity causes the corrosion problem, eliminating it with dehumidifiers removes the problem before it can occur and offer the most significant effectiveness. But, of course, this can only occur if the area can be enclosed; if not, another solution needs to be offered.

hierarchy of Corrosion Control

Figure 1 – Engineering Hierarchy of Control

Lay-up Environment

Figure 2 below shows the annualised minimum & maximum relative humidity from 1984 onwards taken at Changi airport in Singapore and is indicative of lay-up issues across tropical Asia. It offers an environmental snapshot of conditions that must be managed. The lay-up solution needs to consider these conditions and still offer an effective lay-up solution.

changi humidity graph

Figure 2 relative humidity minimum & maximum 1982 to 2015

 Corrosion Management

Corrosion control is essential so it can be eliminated effectively during lay-up. Sodium Chloride (NaCl) accounts for nearly 86% of all salts in the ocean. It is, therefore, the most significant contributor to corrosion. Salt deposition produces deliquescence (becoming liquid or having a tendency to become liquid) at 76% Relative Humidity (RH) for NaCl and 35% RH for MgCl. The corrosion current increases at the corresponding critical relative humidity area. See figure 3 below.

 

corrosion current

Figure 3 Corrosion current at 80% RH & 40% RH

In effect, readings of 76% RH should be avoided along with cycling under this figure.

 

Again look at  Figure 2 above regarding the minimum & maximum relative humidity. You see that Asia offers the perfect corrosion cycle as it rises above 76% RH on an almost daily event as the temperature rises & falls between day & night. Figure 4 below is another example whereby metal is sprayed with salt mist continuously and compared to intermittent salt water spray. It is another example of the corrosion current in action, as indicated in figure 3 above.

representation of effects of corrosion

Figure 4 Effects of corrosion on continuous salt fog versus cyclic salt fog

Solution for Internal Spaces

1. Dehumidification

It aims to eliminate moisture where an area can be enclosed. This strategy is suitable for accommodation spaces, machinery spaces & rooms, empty tanks & cofferdams. Classification societies recommend the following relative humidity readings.

Accommodation                        45%-55% RH

Machinery Spaces                     35%-45% RH

Other Spaces & Tanks              35%-45%RH

Note that higher readings in the accommodation are to stop wood items such as furniture splitting & delaminating of wall panels.

2. VCI Technology

It does not aim at the highest level of effectiveness called “Elimination” but at the secondary level of Engineering Control known as preservation. This method still has issues not resolved, such as humidity in electronics, the moisture level in motors or corrosion under insulation (CUI), for example. Most electronics have a maximum humidity of 95%RH and some even lower where saturation occurs at 90%RH or below, in particular sensors. Many gas detectors suffer deterioration even below this level. Concerning the above humidity chart in figure 2, many electronics start to fail with high humidity. If VCI is used as a means of preservation, then the failure modes of all the equipment have not been addressed, and the reactivation cost is guaranteed to be higher.

3. Do Nothing

Some companies resort to this method, and reactivation costs are the highest.

Conclusion

Dehumidification, where possible, is the preferred method of corrosion control and offers the best solution to electronic & electrical components over all other methods.

Solution for External Areas

1. Dehumidification

It is possible for specific equipment on deck. Still, it involves much work to enclose the space so humidity can be eliminated. In addition, as the highest effective method of corrosion control, it has limited applications. Still, it is worth at times considering specific equipment.

2. Paint Protection

It is the preferred method by classification societies. Any breakdowns in coatings are advised to be made good before/at lay-up to ensure a protective layer to salt spray/ mist. Paint is an ‘Engineering Control’ under the Hierarchy of Control and is considered the primary protection method in large open spaces.

3. VCI Technology

VCI is another method companies are looking at with certain benefits worth considering. As touch-ups are required, VCI should be cost analysed by making good upon paintwork before committing to its use. For the protection of open pressure vessels, tanks and rotating & sliding components, there can be many benefits gained with VCI technology. Still, its application needs to be considered for the right reasons. It is not a one-spray solution to a comprehensive lay-up preservation strategy. MLS does use VCI technology on an as-required basis.

4. Do Nothing

It can be legitimate if the vessel dry-docks upon lay-up. However, it should be noted that the repair cost can be high if the corrosion gets out of control. Therefore, if this method is adopted, a proper monitoring program should be implemented and intervention acted upon before the corrosion accelerates.

Hull

Paint Protection

Put paint protection is the preferred method. Sacrificial anodes are suitable for use where the hull condition has coating breakdown. Testing must be conducted regularly to ensure the proper protection is offered. Different steel grades require a different current reading to ensure adequate protection. MLS uses a special anode that has been specially designed for lay-up operations.

VCI Technology

Overall not suitable for large underwater areas but can be considered for closed sea chests and pressurised lines such as ballast tank lines

Conclusion

Whichever solution you choose for the internal spaces, external areas and hull, the cost versus effectiveness and what cost to do nothing need to be considered. A reactivation plan identifies the best solution to ensure that you, the client stay informed about the cost, benefit and time taken to reactivate. MLS can help with any of these analyses and contact us to discuss further.

 

Best Practices for Marine Lay-up

Garry Best Practises
marine layup of labuan

Class Lay-up Recommendations

Overview

Before committing to lay up a vessel or rig, the first thing to do is look at the latest class recommendations. They continually change over time as new information comes to light. For example, in 2017, one class surveyor reported that over 20 rigs had failed reactivation due to incorrect preservation. Also, some major oil companies are reluctant to accept rigs or offshore support vessels that have been cold stacked for tendering for work. Long-term reliability is a concern. Therefore it is essential to properly understand what is required to be done and work with someone who can best assist in achieving the best outcome.

Are Dehumidifiers Necessary in Lay-up?

During a recent consultation visit to inspect three rigs for lay-up in Labuan, there was much discussion on the importance of dehumidifiers and whether they are necessary. The information below highlights the three main class recommendations for lay-up and should speak for itself as to whether, in Asia, you can afford not to use dehumidifiers. Some rig & vessel owners tend not to use dehumidifiers. It’s essential to understand the benefits of following correct lay-up procedures. By not controlling humidity levels in tropical regions, corrosion accelerates. As such, dehumidifiers are of great importance for lay-up.

 

DNV Lay-up Recommendations

Useful links

DNVGL-RP-0290 Lay-up and re-commissioning of ships and mobile offshore units

Accommodation

Accommodation, including navigating bridge and radio room, should be protected against corrosion and other deterioration by means of a suitable system, e.g., a dehumidified atmosphere with a relative humidity below 60%. Maintaining a dehumidified atmosphere on the navigation bridge is advisable in control rooms and all other rooms containing computers and electronic equipment. The relative humidity should be controlled at regular intervals. Subject to the manufacturer’s recommendations, it may be advisable to keep equipment under constant voltage or put it into service at regular intervals for additional moisture removal and to recondition components.

General

All provisions under section 9.3 apply, except that the temperature in the engine room and other spaces need not be kept above the ambient temperature but not below 0°C. Areas, equipment and machinery, should be protected by the use of a dehumidified atmosphere with relative humidity below 50%. A safe method for keeping this atmosphere under control with regard to humidity should be established, and arrangements should be made to maintain the relative humidity below the given limit. Cooling water should be drained from machinery, dry lay-up of boilers and steam system to be applied.

Hull

Ballast tanks

Ballast tanks in use shall have efficient corrosion protection with coating in good condition throughout. For ballast tanks not in use, a dehumidified atmosphere should be secured, and the tanks sealed off.

Cargo tanks, pump rooms, etc.

A dehumidified atmosphere should be secured for cargo tanks and holds not in use for ballast purposes, pump rooms, cofferdams and pipe tunnels, and the tanks/rooms should be sealed off.

Deck piping

Cargo oil pipes, deck steam pipes, Butterworth lines, heating coils, exhaust, water and air pipes and ballast lines not in use should be cleaned, well-drained, and kept protected by a dehumidified atmosphere.

Deck machinery

Deck machinery which is not needed for instant operation should be protected by a dehumidified atmosphere.

Engine and boiler rooms

The use of a dehumidified atmosphere should protect engine and boiler rooms. Air supply to the engine room for the possible working of combustion engines should be arranged in such a way that the dryness of the atmosphere is not influenced.

Machinery

Reciprocating machinery

The use of a dehumidified atmosphere should protect the crankcase.

Turbine machinery and reduction gears

The use of a dehumidified atmosphere should protect turbine and gear housings.

Freshwater systems

Cooling water systems on engines not in use should be emptied and dried. Care should be taken to remove all water from cooling spaces, and thorough ventilation with dehumidified air is required.

Starting air system

Starting air receivers should be kept empty, clean, dry and open to the dehumidified atmosphere in the engine room. At least one auxiliary starting air bottle should be fully charged to maintain auxiliary engines ready for start-up. It should be confirmed before lay-up that drains are clear. Air piping should be drained and dried out.

Boilers and steam system

Fireside

Arrangements should be made to circulate dehumidified air through the boiler and maintain a dehumidified atmosphere.

Water/steam side

A dry lay-up condition should be used. Then, after careful draining, drying should be executed by circulating dehumidified air through the boiler and the steam system.

Steam system

The whole steam system should be preserved using dehumidified air. An arrangement combined with the boiler should be established.

Electrical installation

General

Local arrangements with dehumidified atmosphere should be established for components such as switchboards, starter boxes, instrumentation units etc. Furthermore, regular control of relative humidity on components and regular change/reactivation of possible drying agents should be carried out.

Instrumentation and automation control room

The control room in the engine room and other rooms containing sensitive electronic equipment should be protected by the use of a dehumidified atmosphere

Lloyds Register

Useful Links

Lay-up Guide. (lr.org)

Accommodation areas

Personnel living on board should be accommodated in one area to allow all other areas to be dehumidified or at least provided with heaters to reduce humidity to an acceptable level. If the ship’s galley is being used by lay-up staff, the galley exhaust fans and grease trap should be regularly inspected and cleaned. The humidity level in accommodation areas should be reduced and maintained at 45-55% relative humidity (RH) by dehumidifiers for all unoccupied areas. This is particularly important for spaces such as the radio room, Navigation Bridge and other spaces housing electrical machinery or electronic control equipment. Ships’ linen and napery should be stored in one dry compartment with mattresses stowed on their edge to assist free air circulation. All provision room, cabin and cabinet doors should be secured in the open position. Water services in unoccupied areas should be shut off and drained, and sanitary fittings and toilet bowls should be sealed.

Machinery

General Machinery

The temperature in machinery spaces should be maintained above 0°C (32°F). Dehumidifying equipment should be installed to protect machinery spaces from atmospheric corrosion by maintaining relative humidity within the range of 30-50% RH. Power should be available for continuous operation of the dehumidifiers and the occasional turning of machinery. To achieve humidity control of the machinery space, funnel openings, grills, ventilator openings, doors, etc., should be closed and sealed. Access to the space should only be restricted to two openings, and it is advantageous if these are double airlock doors.

Diesel Machinery

Main engine crankcases should be supplied with dehumidified air suitably vented at the opposite end of the engine. Reference should be made to the engine maker’s recommendation for laying up. Water cooling systems for the main engine should be completely drained, washed with fresh water and left open to the atmosphere. Air starting valves should be dismantled and lubricated. Fuel valves should be removed, overhauled and stored outside the engine. All bright work should be protected with a smear of grease or oil. Engines, including all shafting, should be turned weekly to circulate oil (e.g. one complete turn plus one-quarter turn). Cylinder lubricants should be operated by hand before turning. Ideally, diesel generators should be maintained in operational condition and operated (rather than turned) once weekly for about two hours.

Steam plant

For lay-ups over three months, boilers should be drained and stored with the drums and header doors open to ensure maximum air circulation.

Water systems

All SW and FW systems and pumps not in use should be washed with fresh water, drained and left open to the atmosphere when a dehumidifier is used. (Otherwise, they should be left full of suitably treated clean water.) Any pumps that are unavailable for power should be turned weekly by hand. Dehumidifiers should be suitably equipped with vent trunking to forcibly ventilate heat exchangers, condensers and steam piping after removing appropriate inspection covers, crank doors, non-return valves, etc.

Electrical, electronic and software systems

Electronic and software systems

A large amount of computer processing equipment is of particular concern when laying up modern ships. Preventative measures must be taken: Equipment containing printed circuit boards should be kept dry and moisture-free, and excessive temperatures should be avoided. The electric supply systems in modern ships consist of electrotechnical components, equipment and systems which could be susceptible to deterioration if the environmental conditions are inappropriate. These systems may require special protection and specialist testing during reactivation. Software back-ups should be made available for reactivation should computers fail to boot up or restart on their own. This may involve keeping all programs and databases (for planned maintenance, etc.) duplicated ashore.

Electrical equipment and machinery

Heating or dehumidification techniques should be employed to prevent condensation within electrotechnical systems where degradation could occur if the environmental conditions are inappropriate. These systems include:

  1. a) main and emergency generators and switchboards
  2. b) all motors and starters associated with propulsion machinery, pumping duties, steering gear, cargo handling, deck machinery and domestic services
  3. c) converters, harmonic filters and transformers
  4. d) all radio and navigational equipment, and
  5. e) all engine, boiler and wheelhouse control consoles.

It is concluded that an inventory of these systems is to be prepared by the shipowner before lay-up, as each vessel has different requirements. Where required, anti-condensation heaters should be provided for those systems located outside the heated or dehumidified areas. Electrical equipment on deck should be covered and sealed, with a suitable method to ensure that any moisture within the sealed equipment is absorbed, such as using a desiccant material. Heaters should be distributed throughout the machinery spaces and those spaces that contain the electrical and control/software-based systems to maintain reasonable temperatures (above 0°C) and prevent condensation.

ABS

Useful links

Guide for Lay-Up and Reactivation of Mobile Offshore Drilling Units (eagle.org)

Guide for Lay-up and Reactivation of Offshore Support Vessels 2021 (eagle.org)

Accommodation Spaces

Accommodation spaces, the navigation bridge, and other control rooms should be sealed and controlled by dehumidification. Complete dehumidification at  45% to 55% RH is typically required to prevent sweating or equipment damage.

Machinery Spaces and Machinery

The machinery and related engine room equipment should be protected against accelerated or localised corrosion, seizing and freezing. This usually involves stabilised or preservative lubricants, prevention of acid concentrations, and regularly scheduled rotation or movement of machinery parts to shift contact surfaces. In addition, there should be a means or source of power for lighting and turning over machinery. Continuous heating for the machinery spaces, including the steering gear room, to maintain a temperature a few degrees above atmospheric; alternatively, complete dehumidification at 35% to 45% RH is usually required to prevent sweating or humidity corrosion damage.

Equipment and engine manufacturer lay-up instructions should be referenced and adhered to.

All rotating machinery in the spaces should be turned over several revolutions and stopped at a new position at least once a month. Where fitted, pressure lubrication systems should be actuated and cylinder lubricators manually operated before the machinery turns over.

The steering gear should be operated and moved full travel at the same intervals. Deck machinery should be turned over at least quarterly. Monthly engine turning may cause the removal of preservative oil from some surfaces. Therefore, the surfaces should be re-covered with preservative oil after the scheduled turning operations. Main and auxiliary engines which are not in operation shall be turned once a month with the main lube oil pump (main engine) and pre-lube oil pump (auxiliary engines) running to ensure oil coverage of bearing journals. Cooling water circulation should also be considered.

Enclosed engine compartments should be dehumidified to avoid corrosion.

Lube oil in engines and turbines should be thoroughly centrifuged and water separated or dehumidified before shutting down. After this, the oil should be analysed periodically to confirm stability and the absence of harmful acidity. Any lube oil reservoir or sump vents to the exposed atmosphere should be closed off and opened only to a dry space. Where lube oil tanks are contiguous with the hull plating, accumulation of condensation should be provided for.

Electrical Installation

The electrical system should be protected against insulation deterioration, primarily from moisture absorption or water ingress, and the rotating elements should be protected against corrosion damage in the bearings.

Electronics are better protected with constant power applied in a warm and dry environment. Sealed and dehumidified ships preserve the equipment longer. Desiccants should be placed inside all electrical units to avoid the risk of condensation. Desiccants should be changed at the manufacturer’s recommended intervals. Open cable ways should be sealed to reduce desiccant degradation and other component damage.

Before securing, electrical motors and generators should be thoroughly cleaned of carbon or other hygroscopic foreign matter, heat dried to obtain good insulation resistance readings, and the bearings lubricated with a stable grease or oil. Any carbon brushes should be lifted to prevent spot corrosion on the commutator or slip rings. Insulation readings should be taken and recorded at least monthly after that, and where found abnormal, immediately corrected by heating, drying or cleaning.

All electrical apparatus should be maintained internally a few degrees above atmospheric through built-in heaters, if fitted, or by other means such as strip heaters or heat lamps. Alternatively, the humidity control may be maintained by opening the unit to the effects of a dehumidifier or by sealing the unit with desiccant. This latter approach would require the replacement of the desiccant and re-sealing at least monthly or based on a moisture indicator.

 

 

Failure Modes in Hot Warm & Cold Layups

Garry Best Practises
Layup in Bay of Brunei

Overview

A question we get asked is what can fail during lay-up. We have been involved in lay-up since 2004 and have decided to highlight some common failures that can occur during lay-up, hot stacking, and warm and cold lay-up. Geographically speaking, it does not matter where your assets are. But, for example, the following conditions could occur.

Hot Layover & Warm Lay-up

As time passes, waiting for a new contract, there can be a lack of understanding of critical preservation needs. As a result, the crew onboard and management are unaware of basic preservation requirements and planned schedules. In addition, leaving specific systems in standby mode for extended periods can cause corrosion and seizure issues, as well as a reduction in the overall long-term reliability of the equipment.

With warm lay-up, issues are pretty much the same as hot lay-up. Still, as time passes and there is no certainty of when the vessel will reactivate, the problems will become more significant issues. I visited rigs sitting idle in the arrival condition 17 months later. Engines had not turned over with forced lubrication; sea water systems were left full of water with the expectation that they may get the word to reactivate tomorrow. The planned maintenance system has not changed, and equipment maintained based on running hours has not been serviced in a suitable timeframe. For this reason, we have done much work creating warm stacking maintenance variants and supplying essential preservation equipment. The below indicates problems that can be found but are not a complete list.

  1. Sea water systems shut down without proper essential preservation.
    • Sea water fouling of heat exchangers
    • Pipe corrosion due to localised corrosion
    • Stagnant water causing stainless fitting corrosion & failure
  2. Treated freshwater systems shut down without proper positive pump circulation
    • Localised loss of corrosion inhibitor & therefore corrosion
  3. Fuel Systems left as per arrival without tank circulation
    • Stratification of IFO & HFO fuel systems
    • Microbial degradation of fuel left standing for a long time
    • Solidification of HFO
  4. Engine start systems
    • Malfunctioning regulators
    • Malfunctioning control systems
  5. Funnel Blanks have not been closed, and exhaust spaces are not clean
    • Rainwater enters economiser spaces, and localised corrosion occurs
    • Hardening of soot due to uncleaned spaces
  6. Jack up rig legs get stuck in the mud
    • Currently, up to 4-day delays have occurred in Labuan due to this event
  7. Transformer oil contamination
    • Large transformers with coolant not fitted with a nitrogen blanket as part of an essential lay-up preservation

 

Cold Lay-up

The atmosphere, especially the humidity, may not have been monitored during lay-up, resulting in corrosion and deterioration.

 

  1. Electronic equipment start-up fails after months without power.
    • Electronic Failure
    • The equipment did not start when power turned on, such as computers, servers and navigation systems
  2. Control system calibration settings off specification
    • The hysteresis curve is out of specification and locks the system from starting, such as DP control systems, boiler combustion systems, and other computer or PLC control systems.
  3. High moisture levels in electrical/ electronic components
    • All products & parts, both electrical & electronic, have operating specifications that generally specify a temperature & humidity range. An enclosed space with no dehumidification will increase the humidity to more than the rating of devices and potentially lead to deterioration and component failure. Lay-up with VCI spray only will cause issues.
  4. Batteries
    • Different battery types have additional requirements, and it does pay to check the class and see advice from the manufacturer
  5. Hull fouling
    • Sea chest fouling reduces water flow. Growth build-up in tropical waters is fast
    • Growth around stern tube seals
  6. The impressed current system turned off
    • Corrosion in sea chests
    • Hull corrosion, subject to paint condition
  7. Ships side valve seizing in the closed position
    • Unfortunate but true, even with proper lay-up greasing before shutting
  8. Corrosion & failure of pressurised seawater pipes or pipes passing through ballast tanks
    • Live sea water pipes will always pose an issue and, unless drained and dehumidified, cannot be actively controlled. Preservation by VCI products may assist with this issue, but unless opened and condition assessed, it cannot be guaranteed
  9. Machinery sitting static for long periods or turned with improper lubrication
    • Pedestal bearings without forced lubrication
  10. Dry powder extinguishers
    • Compacting of powder due to not being turned upside down monthly

The Solution

The above is only part of the problem with incorrect lay-ups. MLS can assist in providing a reactivation schedule to identify materials, labour and time to prepare for departure. Proper planning will assist in preparing to leave without unnecessary delays. So, whether you’re sitting at an anchorage or alongside a wharf, MLS can provide you with a consultancy service that suits your needs & budget.