Ted Berglund and Joe Hughes, Dyplast Products, USA, explain the importance of correct insulation installation

at LNG facilities.

INSTALLATIONInsulation

F ailures at a new LNG facility during the first few months of initial operations can be expensive and cause damage to a company’s image. Therefore, most companies do

everything possible to ensure a ‘perfect start-up’, but this is easier said than done. Identifying what may ultimately cause problems is a first step to controlling and eliminating those problems. Although it may be challenging to anticipate the main reasons for forced shutdowns or curtailments during the first months of operation, poor design and installation of the insulation system are clearly on the list.

A properly designed and installed insulation system on an LNG pipe or fitting is quite a marvel, since across only a few

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inches the temperature can be -165°C at the pipe and 37°C at the jacket – or a delta of approximately 200°C. If a ‘thermal short’ develops in the insulation system (for instance, in a poorly installed expansion joint), the temperature at the surface of the metal jacket can drop dozens of degrees below freezing, and ice can quickly form around the pipe and equipment, making it inoperable and/or posing hazards to personnel. The energy loss can also be significant and, in the worst cases, the natural gas liquid (NGL) in the pipes can begin to boil-off, causing severe problems in pumps and other equipment.

While many of the principles that will be discussed herein are applicable to any insulant, this article focuses on polyisocyanurate (polyiso) and cellular glass (cell glass), since there is more long-term experience with those insulants, with

successful service with no failures over periods of 20 years and more.

Fortunately, poor design of insulation systems is becoming increasingly rare since there are numerous engineering, procurement and construction (EPC) contractors and specifiers who have extensive experience in LNG insulation systems. However, there are still a few engineer/specifiers who depend on ‘the old binder on the shelf’ to help them select insulants and design the system of sealants, mastic, vapour barriers, jackets, pipe coatings, expansion joints, vapour stops, etc. Unfortunately, many older insulation specifications have not incorporated more recent lessons learned, codes/regulations, and advances in technologies/products. For instance, modern vapour barriers are much better than old vapour retarders at very low temperatures; and modern computer-aided fabrication equipment can cut insulation to exotic shapes with close tolerances to fit, for instance, fittings and valves. Also, CINI 2016 has evolved into a comprehensive standard specifically for LNG facilities, and now requires the measurement of many physical properties at LNG temperatures (-165°C), allowing smarter selection of materials and thickness calculations. Similarly, ASTM C591-16 for polyiso and ASTM 552-16 for cell glass require calculation of thermal conductivity across a range of low temperatures, down to cryogenic; and recent lessons learned have demonstrated that the installation techniques for some of the newer insulants being proposed for LNG are flawed.

The insulation systemThe actual installation of the insulation system pipe, elbows and fittings also needs to be considered. Installation practices for those components can be extrapolated to the more complex shapes encountered in equipment. Nominal pipe size can vary from centimetres to over 1 m.

Polyiso and cell glass are manufactured as ‘buns’ or ‘blocks’, respectively. A typical polyiso bun of 40 kg/m³ density typically has dimensions of approximately 1 x 0.6 x 2.5 m; or cut into ‘chunks’ of 1 x 0.6 x 1.2 m. Certain manufacturers can vary the dimensions, optimally accommodate the ‘nesting’ of repetitive cuts, and thereby reduce waste during fabrication. A typical cell glass block with 115 kg/m3 density can be produced in several sizes, the largest of which may be 46 x 92 x 21 cm.

The buns and blocks are then fabricated into the shapes required to cover the pipe, fitting, or component. It may be necessary to glue multiple cell glass blocks together to achieve the optimal dimensions before being fabricated into requisite shapes. Ideally, the fabricated half-shells and any customised shapes fit perfectly to the pipe or fitting with no air gaps (air has minimal insulating value and can trap moisture).

An Insulation segment for a 1 m valve is huge, but can be precisely machine-fabricated in many modern fabrication facilities. Alternatively, insulation for a large fitting can be ‘fabricated in the field’ by manual labour using saws, scoops, and hand-held routers. This latter approach can be even more expensive, depending on labour costs, and the end-product is likely to be of much lower quality. If field fabrication is the choice, the ‘trust but verify’ motto is pertinent, since poor quality field fabrication can be a source of insulation failures during start-up.

Layers and offsetsThe insulant itself is typically applied in multiple layers in LNG applications. Even though it is possible to fabricate a ‘half-shell’

Figure 2. Double layered insulation system.

Figure 3. Double layer insulation system example.

Figure 1. LNG insulation vapour stop.

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of polyiso insulation to virtually any thickness, layering allows for staggered joints, which create a tortuous path for any water vapour in an unlikely breach of vapour barriers. Generally, the same holds for cell glass, yet the much smaller blocks must be glued together to create large sections, and the weight and brittleness of cell glass may limit half-shell sizes. Double and triple layering is common in LNG facilities. A double layer is typical when the overall insulant thickness is less than 12 – 15 cm , and a triple layer when greater than 12 – 15 cm of insulation.

A joint sealer (zero water vapour permeability is ideal) is typically applied on insulation longitudinal joints and butt joints on all layers except the innermost to prevent moisture and moisture vapour infiltration through joints/seams. Joint sealants should be compatible with materials in which it has contact, across the range of in-situ temperatures.

Note that the insulation thickness, the number of layers, and indeed the entire insulation system, must be designed by a competent engineer. For instance, the greater weight of cell glass over polyiso combined with the lower thermal insulating properties may dictate different thickness, layering, pipe hangars,

expansion joints, etc. This brief article must not be relied upon as ‘design guidance’.

Vapour barriersWhile polyiso and cell glass each have excellent water vapour transmission properties, the vast majority of LNG system engineers specify the application of a vapour barrier sheet, slightly overlapped and taped, on the outermost layer of insulation. The specifier/engineer may also require a vapour barrier sheet over inner layers, particularly over the second layer of a three-layer system.

As background, vapour retarders help slow the diffusion of water vapour through an insulation system. Over the past decade, material properties have been improved such that vapour barriers can virtually eliminate water vapour intrusion. A vapour barrier is usually defined as a layer with a permeance rating of 0.1 perm or less (and several manufacturers offer zero-perm products), while a vapour retarder is usually defined as a layer with permeance greater than 0.1 perm, but less than or equal to 1 perm. For a polyiso insulation system, the vapour barrier is typically a zero-permeability sheet consisting of a combination of aluminium foil and/or polyester film and/or mylar. In a cell glass system, the final layer of insulation is typically a coat of asphaltic mastic and an open mesh synthetic fabric.

On top of the outermost vapour barrier, a metal jacket is applied (aluminium or stainless steel), secured with stainless steel straps (no rivets that could puncture the vapour barriers). This jacket protects the vapour barrier from mechanical damage, and can also improve the emissivity (the energy emitted from the surface) and the reflectance (of solar radiation) of the surface, as well as offer some protection to personnel.

Pipe coatingsIt is important to mention that the design engineer should specify whether any coatings should be applied to the pipe prior to the application of the insulant. Many argue that coatings are not required, but a competent engineer should examine the corrosion resistance of the metals (which could range from more exotic stainless steels to carbon steel) in the given environment (wherein temperatures could be much higher than cryogenic during cycling, shutdowns, and so forth). Cell glass installations may require the use of a bore-coating on the inner surface of the insulation in contact with the pipe if the piping undergoes frequent temperature cycles or if pronounced vibration is present.

InnovationsBoth cell glass and polyiso have been in use for well over 50 years. During this period, cell glass itself has not changed much, although there have been improvements in the requisite coatings, adhesives, sealants, and mastics. Cell glass uses ‘air’ as the blowing agent within its cells. Air has poorer thermal conductivities than other more exotic blowing agents, but cell glass manufacturers would likely argue that they do not need to refine their product since it is already environmentally friendly, resistant to moisture and flame, has high compressive strengths, and has reasonable insulating properties. It is left to the engineers to evaluate all of the pros/cons of insulant alternatives.

Polyiso, on the other hand, has evolved considerably, with changes precipitated by external factors (e.g. Montreal Protocol),

Figure 4. Elba Island LNG expansion loop.

Figure 5. Jacket installation over polyiso.

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as well as internal, manufacturer factors (e.g. improved and more bio-friendly products). Polyiso uses increasingly complex blowing agents, catalysts, fire retardants, etc. that are trapped within dense cells, striving to continually improve insulant performance, particularly thermal resistance at low temperatures. Today, hydrocarbons, such as pentane, are commonly used blowing agents in polyiso since they create rigid foam. They are more environmentally friendly than prior generations of blowing agents, while yielding a light weight rigid foam with excellent thermal insulation and other physical properties.

With respect to fabrication innovations, modern computer-aided approaches and more sophisticated cutting equipment allow for faster and more efficient fabrication of shapes that can precisely match custom components. Shiplap, or other more innovative joints, are also increasingly used to add additional tortuous paths for any intrusive water vapour, possibly eliminating an additional layer of insulant.

Case studyPhase II of the Elba Island LNG terminal included an 80% increase in storage capacity at Elba and an increase in the daily design rate of the facility by more than 350 million ft3/d. Upon completion of Phase II, Elba’s storage capacity totalled 7.3 billion ft3 with a send-out capacity of 1.2 billion ft3/d. The expansion project included insulation of 31 895 ft of piping with attendant polyiso insulation.

CB&I, the expansion project prime contractor, specified a two-layer polyiso insulation system for LNG pipe insulation, covered with a combination of zero-perm vapour barrier sheeting, and enveloped in aluminium colour-coded jacketing. Specifications demanded superior physical properties for system components, as well as specific standards for shop fabrication of shaped insulation segments, such as hemi-cylindrical sections, pipe ells for small elbows, mitered sections for large elbows, and tees.

The pipe insulation system scope connected the ship unloading facility with the storage, recondensing, and send-out system, plus the insulation of valves, fittings, and components. The insulation system typically consisted of double-layer insulation for piping with outside diameters varying in size from 3.5 to 41.25 in. Dyplast shipped over 1.25 million board feet of

ISO-C1, in 43 semi-trailers within a period of five months, while maintaining committed shipments to other clients.

After contract award, Dyplast Products worked with its fabrication and installation partners to closely examine manufacturing cost savings, transport economies, fabrication and installation efficiencies, and possible innovations given the specific sizes, quantities, and shapes of insulation to be fabricated. The company’s ability to customise polyiso bunstock dimensions meant that bun sizes could be matched to minimise waste as Dyplast cut the bunstock into blocks (‘pipe chunks’), which were, in turn, sized for minimising waste during shape fabrication by the fabricator, Insulation Materials Corp. Optimally sized pipe chunks also allowed for efficient packing in transportation containers.

Dyplast’s offering incorporated fabrication to support innovative approaches, such as larger/longer insulation sections, interlocking segments, closer tolerances, complex routed shapes, factory-applied laminations, etc., which reduce installation labour, minimise waste, reduce system vapour permeance, and optimise thermal performance. Just-in-time deliveries also mitigated the downside of adequate storage limitations on-site and budget constraints.

The net result was an insulation system that complied with all requirements while adding additional value to the project in terms of costs and schedule. There was no unanticipated downtime, neither during start-up nor in the first months of operations due to the insulation system. 10 years later, there continues to be no downtime, failures, or excess maintenance due to the insulation system.

ConclusionInsulation installation provides a good example of where an owner or turnkey contractor can underestimate the impact and the complexity of an LNG system whose initial capital cost, potential impact on schedule, and long-term performance can have an oversized impact on financial success. While owners and contractors are increasingly recognising the complexities and the impacts of the insulation system and its installation, this article points out the need for up-front knowledge of the issues and their incorporation into specifications, contracts, and the selection of installation contractors.

For instance, an insulation system installed with a single flaw in the vapour barrier can impede start-up. An insulation system with longitudinal joints at 12 o’clock is less risk-mitigating than one at 3 o’clock. Different insulants require vastly different installation techniques. Up-front coordination between the engineer/designers and the installation contractor can be invaluable. Just-in-time deliveries and properly-considered insulant storage strategies can not only minimise breakage and moisture absorption within the insulant, but also better optimise cash flows. Shop fabrication of insulation segments for valves and fittings can greatly reduce labour costs, etc.

Ultimately, insulation system design, installer selection, and installation planning should optimally be coordinated early and simultaneously. By so doing, the LNG facility will be less susceptible to failures during start-up and operations, and will likely be much more energy and process efficient over the years. Any additional cost of proactive attention to detail in the insulation installation will yield considerable return on investment.

Figure 6. Elba Island LNG pipe run.