Essential Cleaning within the LNG Industry
Cleaning the clean
LNG is a famously “clean” industry, but cleaning is still an essential task
The LNG industry stands and falls on the purity of the product. Not only do impurities lower product value but they can also damage plant equipment, raising OPEX and CAPEX costs. Mercury, sulphur and even water are split from the natural gas prior to liquefaction to prevent corrosion of delicate storage and processing equipment.
LNG contamination presents two major problems. Firstly, damaged equipment is costly to replace or repair, with plant downtime compounding the costs. Then the risk of producing off-spec product of an unacceptable standard to clients. These two alone provide plenty of incentive to keep the core LNG pipeline in good condition.
The fact that LNG is sampled at the point of delivery means that storage operators may fail to consider ongoing impact of impurities. Although each shipment should have H2S, sulphur and mercury below the maximum acceptable limit, trace amounts will almost certainly still exist. Over time these impurities build up within transport and storage systems, corroding pipes and other equipment, and contaminating the LNG as it passes through.
The cumulative effect of these impurities is often under-estimated, resulting in damaged equipment or degraded product. Although impurity levels remain low it is essential that the core LNG pipeline, transport and storage systems are checked and cleaned regularly to prevent build up of this harmful deposition.
Due to the colossal daily cost of downtime it is essential that LNG Customers receive a cleaning and inspection service second to none in terms of reducing downtime and out engineering safety risks. Tube Tech International Ltd is such a Company with 30 years of experience within the LNG and Petrochemical industries who guarantee an exemplary service that includes attention to detail and teams of fully employed, highly trained personnel. This culminates in a service that will exceed an LNG customers’ expectation every time.
Ancillary systems also warrant attention
Low concentration of impurities in LNG is not always echoed by the ancillary systems that makes processing, storage and transport possible. Coolant systems, heat exchangers and other associated pipework are all vulnerable to blockages, heat transfer limiting deposits and wear-and-tear.
Where ancillary systems degrade, so too does overall efficiency of the LNG plant. Poor coolant and heat transfer increases boil-off rates during transport for instance. Whilst boil-off can be re-liquefied, doing so adds to OPEX; ideally gas should be liquefied once and kept at boiling point during storage. When coolant system don’t operate at peak performance across the plant, such problems are commonplace.
Although impurities threaten product quality, some also present a significant danger to employees and the wider public. Should water or other water-based coolant compromise LNG transport pipelines, a rapid phase transition explosion becomes a distinct possibility. As well as placing lives at risk, significant damage will have a devastating impact on the company owners .
The 2004 explosion at Sonatrach LNG liquefaction facility in Algeria has never been officially explained, despite 27 workers being killed and a reported $900 million loss. The “US Government Team Site Inspection of the Sonatrach Skikda LNG Plant in Skikda, Algeria, March 12–16, 2004” report suggests that the explosion was caused by a leak from the refrigerant system, rather than LNG stores as originally believed.
The Sonatrach incident serves to underline the importance of properly cleaning and inspecting all plant “using the right contractor with the right equipment” under a routine maintenance plan to identify such risks.
Invariably a separate cleaning and inspection contractor are chosen. The cleaning contractor will typically provide high pressure water jetting or a chemical cleaning service and the inspection contractor the Eddy current, ultrasonic inspection service. The dilemma comes when the cleaning contractor cannot appreciate “how clean is clean” often leaving the inspection contractor to “inspect what he can”. This clearly raises doubts as to integrity and subsequent asset life. Tube tech international avoid this by employing rapid cleaning and inspection technologies that combine both services ensuring every area, be it a shell and tube heat exchanger, pipe or tank surface area is cleaned to the desired inspection standard every time without fail. The inspection results are then handed over to the client for independent assessment.
Real world examples
The need to clean LNG systems regularly is not just a theoretical construct. Some businesses have already learned the true cost of failing to clean their “clean” systems completely. Great care is given to the shell and tube condensers, air cooled condenses as well as the pipework supporting the LNG transport system in order to prevent introduction of contaminants, but the same level of care is rarely afforded the surrounding plant infrastructure. The reason for this is quite simply the antiquated cleaning methods employed by indigenous, poorly managed cleaning contractors who do not appreciate “how clean is clean” nor achieve inspection standards required in the shortest time period needed.
Routine inspection of LNG pipework and supporting systems often leads to the discovery of problems, but standard cleaning techniques are unable to restore full working order in the timescales allowed. This means that plant cooling systems are often part-cleaned, marginally improving efficiency but leaving the potential for further contamination and the build up of harmful deposits due to the surface key way left behind.
African LNG plant pay price for ineffective inspections
This particular LNG plant discovered several problems at their processing facility following a routine inspection of the plant’s cooling system. Impurities in the cold water supply had led to significant build up of blockages and iron oxide deposits within their shell and tube condensers which contaminated the rest of the cooling system.
The spaghetti like 6 inch – 32 inch delivery pipework also became fouled but because it was not designed to be pigged online the client was unable to remove deposits without shutting down. Plant operators were forced to declare the cooling water condenser system “un-cleanable using traditional chemicals and water jetting”
The fouling caused this client to take the system offline whilst sophisticated and rapid cleaning technology was employed to get the plant online to avoid a multi-million dollar loss of downtime. Such was the success of adopting a bespoke cleaning and inspection procedure, the plant was able to resume normal operation at maximum efficiency within a fraction of the time that would be needed for traditional water jetting and chemical cleaning methods, without having to replace large sections of their cooling system.
Time and time again it has been proven on a global scale that traditional cleaning and inspection services are both outmoded and in almost every case have not progressed further than the traditional “three men and a pump” approach. LNG plants much like refineries and petrochemical plants are designed using 90-year-old, traditional shell and tube ASME / Thema designs, in other words nothing much has changed. Similarly the pipework is installed without much forethought as to how it might be accessed and therefore cleaned and inspected should a fouling situation occur. Designing in the ability to access, clean and inspect a plant in situ and even online requires only a consortium of customer, designer, fabricator and competent cleaning and inspection specialist to create this solution. The cost at new build stage is negligible compared to the overall multibillion-dollar budget.
Microbial activity costs $30 million per day
Any shutdown is bad news, but for an unspecified LNG plant in the Middle East, taking the systems offline cost an estimated $30 million per day. However the discovery of a fine film of tenacious manganese oxide scale was discovered on the inner surfaces of 20,000 heat exchanger tubes, the plant operators had little choice but to shut the system down for cleaning.
As with the African plant, maintenance had identified an issue previously, but traditional even specialist 40,000 p.s.i. UHP cleaning techniques failed to remove the fouling without damaging the tubes. All condensers had to be cleaned in situ. If a cleaning method could not be found meant that the alternative was replacement or re-tube incurring substantial delay and expense.
To avoid further financial losses for each failed cleaning attempt with traditional contractors a new method was deployed that had been fully researched and proven which provided the customer with a fully polished tube bundle that restored the bundle to “as new”. Although the actual cause of manganese oxide and associated corrosion was unusual, applying the same care to the heat exchanger as to the LNG pipes guarantees to reduce cleaning and downtime costs.
When clients require a cleaning service they can be forgiven for not asking the right questions of a cleaning contractor that utilise water jetting or chemicals as their preferred method, when a tender document goes out. It is safe to say that most clients take the attitude “it’s been done this way for so long, why change” approach and hence old dusty files come out and the same tendering procedure is used. For which one can of course be forgiven, as cleaning technologies have grown in parallel to old design of heat exchangers and pipework, i.e. not much has changed. There is however a little-known international company who has successfully researched and developed over 50 unique, tried and tested technologies that challenge convention and which realise spectacular savings that otherwise remain un-tapped.
Into the future
The development of new floating LNG (FLNG) plants is set to further increase the importance of proactive cleaning of pipework and systems. Not only are ship-based processing plants more compact and difficult to operate in, the additional atmospheric factors, such as salty sea air, will force operators to inspect, clean and maintain machinery more often.
Operators will need to closely monitor all aspects of the FLNG platform for signs of corrosion, leaks or deposits. Because of the hostile operating environment, maintenance and cleaning will need to be performed all the more regularly too. It is not unlikely that FLNG trains will be subject to more frequent shutdowns than their onshore counterparts to facilitate bare metal polishing both inside and outside the system.
Counting the cost of LNG cleaning
As with any complex system, the peak performance of all inter-related components is essential to maximise efficiency and profit. Cleaning cycles can be combined with inspection of inner pipe walls to maximise use of downtime and to identify and repair damage early.
However it is also clear that “good enough” interim cleaning of LNG systems could actually be creating larger problems over the longer term. . Operators also need to carefully consider the cost of using partially-effective techniques regularly over a single bare-metal polish. Even if the liquefied gas remains uncontaminated, other pipework and machinery could bring production to a halt at enormous cost to the operator
And it is for this reason that the even the “clean” LNG industry may benefit from dusting the cobwebs from its traditional, outmoded way of thinking and tendering.