The how and why of Cryogenic insulation. And: who is responsible for insulation design?

Drawing up a good and clear insulation specification is one thing, but incorporating this specification with piping and equipment design is something else.

Get any cryogenic insulation expert to talk and they will tell you a dozen different examples of unfriendly conditions in which contractors often need to carry out their job. These examples are not from an environmental point of view. Of course, extreme artic or tropical conditions can pose an additional challenge to meet high quality standards. However, insulation contractors are a special breed and know how to deal with this. No, the examples have more human related causes.

In this article, issues are addressed which insulation contractors often have to take for granted, but can be easily solved in the early design phases of a project. Or more specifically, the way LNG installations, piping, and equipment are designed without taking cryogenic insulation into account. During the engineering phase of an LNG project, piping and equipment designers often refer to standardised details when it comes to insulation. Design details (insulation support rings, nozzle stand-off, orientation and design of valves) are not always reviewed or updated, and are often just a footnote in drawings.

Also, during 3D modelling, where piping plots and equipment locations are determined, checks are limited to clash detection or checking valve and instrumentation accessibility. No attention is given to check if equipment and/or piping can be insulated, which during erection leads to situations where insulating contractors have to crawl with difficulty to install insulation.

This raises the question: Who is responsible for insulation design? If you look at most piping and equipment designer education programs, hardly any attention is paid to the impact of insulation. Aspects like thermal dynamics, heat loss calculations and sometimes an overview of different insulation materials are included, but there is no focus on the influence of piping/equipment design in relation to the way this object needs to be insulated. As a result, insulation contractors have to push the envelope to design insulation details to get around certain details. For example, lifting trunnions or lugs on equipment – they only serve a purpose during installation/erection. However, when insulating them, they can become potential water ingress points. Or in the case of cryogenic insulation, a point where a vapour barrier can fail. So, why not design removable trunnions or lugs? There are several more details which a piping/equipment designer should be aware of. Addressing these details during the design phase will improve the quality of cryogenic insulation. Not only the quality of the end result but also the level of performance during installation. Do most piping/equipment designers understand the fundamental basics of cryogenic insulation? Why do cryogenic-insulation systems have much more detail compared to hot-insulation? Cryogenic-insulation is not an exact science, but the result of decades of experience, trial and error, leading to best practices. And behind all these details there is an important history to understand. Engineers who have this understanding design better piping/equipment in relation to insulation.

Why is cryogenic insulation often build up as a multilayer system.

According CINI (Committee Industrial Insulation), for cryogenic insulation systems, closed cell insulation materials are still regarded as best-practice. In most projects, closed cell is translated into cellular glass (CG) and poly-isocyanurate (PIR). Although other type of insulation materials are currently being reviewed by CINI, CG and PIR are based on their track record, still considered as best-practice. However, these materials are rigid, or in other words not flexible and have a linear expansion coefficient which causes them to contract when the cool down. In order to avoid internal stress build up, due to the temperature difference between service temperature (LNG -165°C) and environmental temperature in relation to this linear expansion coefficient, a multi-layer system is designed, where every individual insulation layer can accommodate the temperature gradient.

Contraction joints.

During cooling down, there is another linear contraction difference occurring, namely between piping/equipment material and the insulation material. This difference is result of different linear expansion coefficients from piping an insulation material. And to accommodate this difference and the previous described phenomenon, contraction joints need to be installed. The position of these contraction joints should be mentioned in the insulation specification. And during piping/equipment design the exact position should be indicated on isometrics and drawings. In a horizontal piping system, a contraction joint should be located preferably in the middle of two fixed points. This can be a pipe-support, fitting (bend, Tees) or valves. In vertical piping/equipment a contraction joint should always be located direct under insulation support rings

Vapour stops

Vapor stops service the purpose of creating compartments to assure that any failure in the insulation system doesn’t spread out further than the compartment boundaries. And water or moisture ingress stays within the confine of two vapor stops. Vapour stops are build up by applying a cryogenic sealant/adhesive that is dressed up from the pipe all the way over the insulation layers up to the outer surface. In order not do disrupt or brake the vapour barrier due to linear movements during cooling down, vapour barriers should always be installed at fixed points.

Fixed pipe-supports

Pipe-supports in cryogenic insulation are always cold-bridge-free designed. Therefore, there can be no contact between steel structure (clamps, shoes) and pipe. By using HD-PIR support cradles, the steel structure can be installed outside of the vapour barrier. Piping designer use two basic types of piping support: a fixed or a sliding-support. Whereas in the insulation branch a cryogenic piping support is always a fixed point. There is no movement between the cradle and the pipe. As previously mentioned, the position of contractions joints is located between two fixed points and with pipe-supports being fixed point (or anchor point) the contraction of insulation material is directed from the contraction joint toward the fixed point.

Primary/secondary vapour barrier

The purpose of a primary vapour barrier is to most people quit obvious. To avoid water or moister ingress into the insulation system. It′s a basic law of physics that moisture migrates towards the lowest water vapour pressure rate. And moisture or water that penetrates into insulation materials due to a failed vapour barrier, will deteriorate the insulation material properties. Most important: thermal conductivity. But when moisture gets subzero it turns to ice. And everyone know ice expands. So as a result will damage and crack up the rigid insulation material.

The purpose of the secondary barrier is more subject of discussion. Some people question the need based on insulation materials properties. Other claim it’s not a secondary vapour barrier at all, but a slip layer. Rough insulation material surface makes linier movements between different insulation layers due to contraction more difficult. And could result in damages during cool down. Hence the need to introduce a smoother surface, which is a mylar-foil. This smooth foil does not only make linear movements possible, it also has a very low permeability. And therefore can act as an secondary vapor barrier. But the most wide accepted argument is, that it is primarily a secondary vapour barrier. A back up in case the primary gets damaged. Again, an example of best-practice raised from trial and error.

Best Practice

But when is something to become a best-practice? And who determines this? And how do become best-practices a standard for the industry.

CINI has 3 decades of experience in this process. With several technical committees, consisting of a cross-section from the insulation supply chain. With a revision commission from asset-owners looking over the shoulder, judging if any outcome is undisputable and can receive broad support from industry, CINI achieves a vital role in a process from innovations to recommend to best-practices. Closely affiliated to CINI is NCTI who organizes training, certify CINI inspectors, but also carry out insulation inspections.

Both organizations have created an independent and objective position in the industry. Insulation contractors always complain there the last thought in a project. With tight project schedules and the conditions mentioned, it becomes an almost impossible job. CINI/NCTI wants to help but it’s a long way. Awareness at asset-owners, who plan new LNG projects, should in the FEED stage pay attention to insulation specifications. EPC contractors should address insulation design details during piping and equipment design and after commissioning and start-up. Asset-owners should check if they have as-build documents. Inspection and maintenance should have inspection and maintenance procedures and programs. There is still a lot of work to be done to end with a generation of insulation contractors who are in a better position