CUI and Challenge the Need for Insulation

Introduction

It’s my standard statement: “CUI is a mine field”. And for more than just one reason. It’s not only a hidden phenomenon, also companies who don’t invest in a good CUI mitigation strategy, sooner or later going to get their names in the papers, due to unwanted accidents, production loss and environmental damages. Just Google for 5 minutes to get you proofs to my statement.
But when proverbial horse has bolted, a lot of asset-owners, want to closed the stable doors by implementing rigorous measures. And with the risk of getting serious SHE issues they often only focus on a short term solutions. Which is dismantling entire thermal insulation, in some cases welding were wall thickness loss is critical, recoat equipment or piping and than reinsulate. In most cases with the same insulation system as before.
If we really want to learn from our “mistakes” we definitely should think about long term solutions to mitigate CUI and minimize future CUI failure.
Of course this takes an effort in all phases of the life cycle and starts with senior management allocating enough budget.
But in this article I′m only focussing on what I think is the first step in the life cycle: Engineering.
From engineering point of view we need to look at the whole system and make choices about:
1. Metallurgic for equipment/piping
2. Surface protection: coating or metallisation (TSA)
3. Insulation material
4. Cladding or jacketing

In this article I will discuss more in depth items 3 and 4 and share recent insights and practices.

What is CUI?
Of course to most corrosion experts an “open door” but in recent years I’ve seen a variety of people dealing with CUI who have little or no background about basic physical principles about corrosion.
Therefore a small summary. CUI is a collective noun for various types of corrosion mechanisms. But it’s always caused by the presence of (rain)water containing chlorides and or sulphates. For carbon steel CUI only occurs in combination with a failed or damages coating system. And can manifest as pitting corrosion or uniform wall thickness loss. For austenitic stainless steel most common form is external chloride stress cracking corrosion (CL-ESCC).
Water which eventually can accumulate onto the substrate and could form an electrolyte can origin from various sources.
? Rainfall or heavy mist
? Drift from cooling towers
? Deluge systems
? Process leakage or spillage
? Condensation within the insulation systems

CUI can be expected on piping and equipment operating between -4°C (25°F) and 175°C (347°F). But also systems operating outside this range e.g. cyclic temperatures or dead legs can be susceptible. As said CUI is a hidden failure. It can occur locally or can affect a larger area.
Although corrosion rates for carbon steel are in general lower than CL-ESCC rates. For carbon steel, especially near seaside salty environments corrosion rates up to 20mils (0,5mm) per year have been reported4).

The role of the insulation system
It’s a common consensus amongst experienced people dealing with CUI: ”Dry insulation systems in the long run simply don’t exist”. And therefore as a rule are regarded as a bad influence. Also for decades people believed that cladding/jacketing was 100% weatherproof and in combination with elevated service temperatures water or moister never could get trapped. This idea resulted in many cases that piping, other that the basic shop primer, wasn’t even extra coated.
?

Cladding/jacketing is primarily designed as a weatherproofing and not as a vapour barrier. Depending on service temperature in combination with ambient conditions, condensation within the insulation system therefore can’t be avoided and needs to be addressed in the engineers phase.
In other situations water enters into the insulation system through a failed or broken cladding/jacketing.
Causes can be:
1. Foot traffic
2. Inadequate design
3. Incorrect installation
4. Insufficient maintenance strategy

Overlooking all possible CUI causes in relation to a consequence of failure of piping systems or equipment it′s therefore justified to: “Challenge the Need for Insulation”.

The oil crisis during the seventies brought new insights on energy savings and resulted in other design criteria for thermal insulation for the (petro)chemical industry. In some cases this resulted in excessive insulating which not always was economical substantiated. However recent geopolitical CO2 reduction goals persuaded many asset-owners to re-evaluate these old goals and translate them into new company policies.

Below link shows a flow diagram which provides a few logical steps to understand if insulation is necessary or maybe can replaced.

Flow diagram

Reason for insulating
The first question always to be answered is the reason for insulating which can be one or a combination from following:
? Heat conservation or energy saving
? Process control
? Freeze protection/winterisation
? Personnel protection
? Noise reduction
? Fire protection
These reasons determine the choice of insulation materials and the type of cladding/jacketing.
There are various insulation standards and guidelines but I would like to recommend CINI industrial insulation manual 2).

When going through above flow diagram we see that only insulation for personnel protection reason (PP) could maybe be considered for removing and replaced with something like protective guards. But as said with recent environmental en energy saving goals this should be a critically assessed.

Designing a fit-for-purpose insulation system

There isn’t a “one-size-fits-all” insulation system. And therefore insulation design should be more that just to draw up a specification. Piping engineers and equipment designers should make detailed insulation design. Based on a consequence of failure assessment, piping and/or equipment with a higher ranking should have a insulation systems with the lowest susceptibility. In order to so following criteria need to be considered when designing insulation systems:

1. Insulation materials choice (hot, cold of P.P.)
Insulation materials can be roughly subdivided in permeable (open) and impermeable (closed cell) materials. For systems below ambient conditions were surface condensation or icing is possible, often closed cell materials like PUR/PIR foam or cellular glass are chosen. Whereas for hot systems mineral wool like stone or glass wool or expanded perlite are common products.
The choice also depends on local or historical grounds. For instance Europe uses a lot of mineral wool for hot insulation as were USA calcium silicate, perlite and cellular glass are more common. In specifications it’s common practise not to refer to product names and therefore many insulation specification refer to general technical requirements.
Important characteristics in relation to CUI are:
? Water absorption (ASTM C610 or ASTM C612)
? Leachable chlorides content (ASTM C871 or ASTM C795).
? hydrophobic behaviour
? Compressive strength (when foot traffic can be expected)
? Dimensional stability

2. Insulation cladding or jacketing
The first step is to determined the purpose for cladding or jacketing. There are several design criteria such as:
? Vapour barrier (below ambient service temperatures)
? Weather protection and UV resistance
? Mechanical resistance
? Accessibility for maintenance or inspections
Cladding/jacketing can be subdivide into metal an non-metal with each specific characteristics and scope of applications. Although above criteria determine the choice this is also influenced by local available craftsmanship and practices. Another important part of the cladding/jacketing is the use of caulking or sealants. The choice whether all joints (longitudinal, circumferential as well as protrusions) shall be finished (of flashed) depends on how sheeting details are designed.

3. Local geographic conditions and plant layout.
Sea side environments are different from inland. And artic conditions differ from tropical. Also down wind drift from cooling towers or frequent fire deluge drills are determinative issues. In Europe this result that many sites are classified in the highest corrosion class. Also it’s important to create enough distances between piping and equipment to allow proper insulation installation and later on enable maintenance and inspections.

4. Equipment/piping/tank design details.
For pressure piping or equipment sufficient standards and codes like ASME, API, BS, Lloyds are available. But details with regards to insulation design often are limited to e.g. clips or insulation support rings. And some of these details in fact can create potential ingress points. The bridge between mechanical design an insulation design is a giant leap forward in mitigation CUI. And below suggestion could add a big improvement
? Collars on protruding tubes.
? Vacuumrings which don’t retain water
? Lifting lugs which easily can be removed after installation
? Pipe support on high density
For further design details I refer to the EFC CUI guideline 1) and CINI industrial manual 2).

5. Installation procedures
Safety, Health en environmental conditions are different per country or region. It′s important to verify installation and application guideline provided by the manufacturer and verify this with applicable legislations and rules. SHE requirements regarding e.g. fibres, dust, solvents etc. can influence the choice.

6. Inspection en maintenance practices.
Clients own inspections procedures can require inspection plugs or access points for visual inspection or NDE. But also accessibility for maintenance purposes, for instance to enable to easily change gaskets can determines insulation design for valves. It’s recommendable to use clients best practices and lessons learned from the use-phase regarding insulation.

QA/QC during erection is often left to the insulation contractors organisation. But recently I’ve seen many asset-owners investing in independent autonomous QA/QC departments. Who also drawing up inspection and test program’s (ITP) in where critical “hold” and “witness” points are checked. These steps are vital when after commissioning setting up an RBI inspection and maintenance strategy.

7. Life Cycle Costs (LCC) Total Cost of Ownership (TCO)
Two terms which to some of us appeal more like senior management gibberish. But in my experience companies with a good working CUI mitigation strategy have a maintenance manger who’s able to convince the senior management about the link between “overall equipment efficiency” and a CUI inspection and maintenance policy. And since CEO’s talk in terms of money these figures become important. One thing all studies have shown: Thermal insulation has a return on investment (ROI) of less than 2 year

But even when given thought to all above mentioned criteria, CUI still can happen. It’s been reported under every type of insulation material and cladding and even in newer installations. NACE, API and EFC refer to insulation systems which: “holds the least amount of water and dries most quickly to result in the least amount of corrosion damage to equipment” 3). And as a, maybe logical consequence, impermeable closed cell insulation materials and vapour tight barriers seem to be the best option. But even then: operation conditions (thermal expansion/contraction), foot traffic, failing caulking at protrusions still can damage these systems and cause water ingress. Which brings me to my opinion that following options should be considered.

Option 1: Non-contact System
If wet insulation in contact with the substrate is the cause to all these problems why not detach by creating a cavity between insulation and substrate. This is called: “non-contact insulation”. Although the idea is evident and being used by Statoil and Shell, never the less some details needs to be addressed. For instance the spacers used to create this cavity may not create a crevice to allow crevice corrosion.
Depending on the service temperature, especially for vertical columns, within this cavity a vertical free hot air flow can create extra convection and consequently extra heat loss. But this can easily be minimized by making compartments and can be compensated with a higher thickness.

Option 2: Aerated insulation system
Moisture will always condensate were water vapour pressure rate is at it lowest and at the coldest spot. In thermal insulation this is the cladding/jacketing. By creating an air cavity between insulation material and cladding/jacketing, moisture has not only the possibility to freely condensate but also find its way to the lowest point were it can escape through a drain hole.

Both options are not new and implemented by companies like Shell, Statoil and DOW. Also it’s documented in the CINI industrial insulation guideline2) and standard like Norsok, DIN and AGI-Q. But for some to me unknown reason not widely known within the insulation branch. Although some big asset-owners are behind these systems, it’s important that independent testing should give more scientific and reliable data which can lead to better standardization.

Lifecycle versus investment
It’s obvious these options come with a surcharge in comparison to traditional ways of insulation. And without fundamental research and testing it’s plausible that, although water still can ingress, it has a way to get out. In other words these systems are less susceptibility to CUI. And as a result contribute to expected lifecycles. Will these system increase inspection intervals? This depends on more factors. But with option “1” endoscopic visual inspections are a possibility and large scale insulation dismantling is nog longer necessary.
Still broken or damaged cladding/jacketing needs to be repaired. But in this case you can feel more confident that water that has gone in sooner or later will get out.

New developments
The technical insulation market is not famous for it′s inventiveness. Never the less some simple bright ideas have being developed over the last years. For instance:
? Moisture detection systems.
? Insulation with a build in wicking.

The International Standard Organisation ISO has under TC-67 formed a working group WG11 who is going to develop ISO/NP 19277 (Methods for Control of Corrosion Under Thermal Insulation and Fireproofing Materials) Part of the standard is to develop a standard which insulation systems can be tested and evaluated for the contribution to CUI. A necessary step in order get worldwide accepted and independent procedures and open new ways for product development on a system level. And as member is see it a challenge to build the bridges as mentioned in this article.

Finally
CUI is nothing new and a lot of solutions in this article are know for years. For me there are in the years to come two major steps necessary to control CUI. Education and mind-set. In the last decades due to cutbacks a lot of know –how has gone, especially with asset-owners. And since it’s impossible to get a bachelor degree in Industrial Technical Insulation this knowledge gap has being filled in by insulation manufacturers and contractors. But since their expertise is thermal insulation and CUI is a corrosion issue some bridges have to be build and knowledge to be share. This start with the changing the mind-set. CUI mitigation is a systems approach: metallurgic design, surface protection, insulation material and cladding/jacketing. By combining these disciplines within engineering an important step forward can be made.
And as member of ISO TC67/WG11, CINI and EFC I see it a personal challenge to build these bridges and keep on sharing knowledge.

References
1. EFC WP15 CUI guideline (www.efcweb.org)
2. CINI manual for industrial insulation (www.cini.nl)
3. NACE SP0198
4. Lyondell Chemical Netherland BV, CUI Study