CUI Prevention — Corrosion Under Insulation with Calcium Silicate Systems

Published: 2026-08-05 | By Mingfa Technical Team

Corrosion under insulation (CUI) remains the most persistent and expensive integrity threat in hydrocarbon processing, chemical manufacturing, and power generation. It accounts for more unplanned downtime than all other failure causes combined in oil and gas facilities, according to multiple industry integrity surveys spanning 2010 to 2023. An estimated 40 to 60% of piping maintenance budgets at refineries and petrochemical plants are consumed by CUI-related inspection and repair. The problem is compounded by its invisible nature: less than 1% of the pipe surface beneath insulation is visible through inspection ports or removable covers at any given time. The remaining 99% corrodes unseen until a leak, rupture, or scheduled strip-and-inspect event forces discovery.

Calcium silicate insulation presents a specific CUI management challenge. Its hygroscopic nature means it absorbs and wicks moisture. Its chemistry can introduce corrosive ions into the trapped water layer. And its typical application temperature range — steam pipes, process heaters, distillation columns — overlaps the most aggressive CUI window. This article covers the CUI mechanism, how calcium silicate contributes to it, prevention strategies validated by NACE and ASTM standards, inspection technologies that detect corrosion without full insulation removal, and a decision framework for repair versus replacement.

1. What Is CUI and Why It Matters

Corrosion under insulation is the external corrosion of carbon steel or stress corrosion cracking of austenitic stainless steel that occurs beneath thermal insulation when moisture penetrates the insulation system. Three conditions must coincide for CUI to initiate on carbon steel: liquid water must be present at the metal surface, oxygen must be available, and the metal temperature must be within the range where electrochemical corrosion is kinetically favorable.

The temperature window for aggressive CUI on carbon steel spans approximately 25 to 350 degrees F (minus 4 to 175 degrees C). Within this range, water exists in liquid form long enough to sustain corrosion reactions. The most severe attack concentrates at 140 to 300 degrees F (60 to 150 degrees C), where intermittent wetting and drying cycles concentrate dissolved salts through repeated evaporation. Each thermal cycle — a unit trip, a process upset, a scheduled shutdown — drives the mechanism: water trapped in the insulation migrates toward the hot pipe surface, evaporates, and leaves behind chlorides and sulfates at progressively higher concentrations. Over months and years, salt levels at the pipe surface can reach several thousand ppm, far exceeding the threshold at which pitting initiates on carbon steel.

The scale of the problem is driven by the inaccessibility of the corroding surface. Typical insulation removal cycles for process piping at refineries run 15 to 20 years. Between strip-and-inspect events, less than 1% of the insulated surface area is visible through inspection ports. A 2019 NACE impact study estimated that CUI costs the global hydrocarbon processing industry $30 billion to $50 billion annually when accounting for direct repair costs, production deferment, and consequential damage from leaks and ruptures. CUI is not the largest corrosion cost category — that distinction belongs to atmospheric corrosion of structural steel — but it is the most operationally disruptive because failures occur without warning on pressurized hydrocarbon lines.

For maintenance managers, the operational calculus is straightforward: a single CUI-driven pipe failure on a crude unit or reformer can result in a unit shutdown lasting 5 to 14 days, with production losses in the range of $500,000 to $2 million per day for a medium-sized refinery. Preventing that failure through systematic coating, material selection, and inspection costs a fraction of one day of lost production. The economics of CUI prevention are not marginal — they dominate every other line item in the turnaround maintenance budget.

2. How Calcium Silicate Contributes to CUI

Calcium silicate insulation is hygroscopic: its crystalline xonotlite structure (6CaO · 6SiO₂ · H₂O) contains microporosity that readily adsorbs and wicks liquid water. In a properly installed system with intact vapor barrier and sealed terminations, this property is managed. In the field, where jacketing sustains mechanical damage within months of installation and sealant degrades under UV and thermal cycling, water ingress is inevitable.

The water transport mechanism is capillary wicking. Liquid water entering through a breach in the outer cladding — a half-inch tear in aluminum jacketing is sufficient — spreads laterally through the insulation by capillary action at rates far exceeding what vapor diffusion alone would permit. Once the insulation is wet, the outer cladding acts as a vapor barrier that traps moisture against the pipe surface. Field measurements have documented insulation moisture content of 15 to 40% by weight at the 6 o'clock position of horizontal pipes within two years of a cladding breach, even when the pipe operates at 350 degrees F.

Chemical contribution is the second mechanism. Commercial-grade calcium silicate insulation contains residual chlorides and sulfates carried through from the raw materials — quicklime, silica flour, and process water. When the insulation becomes wet, these water-soluble ions leach into the trapped moisture layer at the pipe surface. Chloride concentrations in the leachate have been measured at 50 to 500 ppm in standard-grade calcium silicate, sufficient to initiate pitting on carbon steel and chloride stress corrosion cracking (Cl-SCC) on 300-series stainless steel. Sulfates contribute to acidic conditions; leachate pH values as low as 4.5 to 5.5 have been documented in field extractions from wet calcium silicate insulation. At these pH levels, the passive oxide film on carbon steel is unstable and general corrosion rates accelerate.

Field data reinforce the laboratory findings. At one California refinery, a post-turnaround survey of calcium silicate insulation removed from a crude unit's atmospheric pipestill overhead line found that 50% of the removed material was too degraded by moisture absorption and chloride accumulation to be reinstalled. The pipe surface beneath showed pitting depths of 0.040 to 0.080 inch (1.0 to 2.0 mm) after approximately 12 years in service. The insulation had been installed with aluminum jacketing and standard vapor-stop sealant; the primary water entry points were identified as failed caulking at valve stem penetrations and mechanical impact damage to the jacketing during adjacent maintenance activities.

These failure modes are not unique to calcium silicate. Mineral wool absorbs water equally readily and introduces its own chemistry. The difference is that calcium silicate's rigid structure provides no visual warning — unlike mineral wool, which visibly sags and compresses when waterlogged, calcium silicate retains its dimensional form while holding water internally, masking the problem until the pipe surface is exposed.

3. CUI Prevention Strategies for Calcium Silicate Systems

Preventing CUI under calcium silicate insulation requires a multi-layer approach: protective coating on the pipe surface, material specification for the insulation, and design features that manage water ingress and drainage. Each layer is addressed by a specific industry standard.

3a. Immersion-Grade Protective Coatings per NACE SP0198-2010

NACE SP0198-2010, "Control of Corrosion Under Thermal Insulation and Fireproofing Materials — A Systems Approach," is the governing standard for CUI coating selection. The standard defines nine coating systems for carbon steel (CS-1 through CS-9) and additional systems for austenitic stainless steel. For calcium silicate applications, three coating types cover the operating temperature spectrum:

CS-3: Epoxy Phenolic. Service range minus 50 to 300 degrees F (minus 45 to 150 degrees C). Applied at 100 to 200 microns (4 to 8 mils) dry film thickness per coat, typically in two-coat systems. Epoxy phenolics offer good chemical resistance and are the most widely used CUI coating for steam and hot water piping in the moderate temperature range. They bridge the full CUI corrosion window while remaining cost-competitive. Cure time at ambient temperature is typically 24 to 48 hours before insulation installation.

CS-4: Epoxy Novolac. Service range minus 50 to 400 degrees F (minus 45 to 205 degrees C). Applied at 100 to 200 microns (4 to 8 mils) DFT per coat. Epoxy novolacs provide higher crosslink density than standard phenolics, offering improved chemical resistance and higher temperature tolerance. They are specified for process piping operating above 300 degrees F where standard epoxies begin to oxidize and embrittle. Some formulations incorporate silicone modification for additional thermal stability.

CS-6: Inert Multipolymeric Matrix (IMM). Service range minus 50 to 1,200 degrees F (minus 45 to 650 degrees C). Applied at 100 to 150 microns (4 to 6 mils) DFT per coat. IMM coatings are ambient-curing inorganic/organic hybrids that form a ceramic-like barrier after heat exposure. They cover the full calcium silicate application temperature range, including high-temperature process heaters and furnace backup insulation where organic coatings fail. The inorganic character eliminates the oxidation and pyrolysis mechanisms that degrade organic binders above 500 degrees F.

Coating selection must account for the full operating cycle, including shutdown periods when the pipe surface cools to ambient temperature — the most CUI-vulnerable condition. A process line operating at 600 degrees F during normal service cycles through the 25 to 350 degrees F CUI window every time the unit shuts down. The coating must perform at both ends of the temperature range.

3b. Proper Installation: Vapor Barrier, Terminations, and Drainage

Even the best coating is undermined if the insulation system admits and retains water. Three installation details determine long-term CUI resistance:

Continuous vapor barrier. The outer jacketing — typically 0.016 to 0.024 inch aluminum or 304 stainless steel sheet — must form a continuous moisture seal with minimum 2-inch circumferential overlaps oriented to shed water downward. All longitudinal seams should be positioned at the 4 o'clock or 8 o'clock position on horizontal pipe, never at the top (12 o'clock) where standing water can penetrate, and never at the bottom (6 o'clock) where gravity-driven flow concentrates.

Sealed terminations. Insulation terminations at flanges, valve bonnets, instrument connections, and pipe supports must be sealed with flexible elastomeric vapor-stop mastic that bonds to both the pipe coating and the insulation. The termination detail should extend the coating a minimum of 2 inches beyond the insulation cut line to prevent moisture wicking under the insulation edge. Pre-formed termination shields or "cannon" fittings at valve and flange assemblies should be used rather than field-fabricated sheet metal wraps, which are prone to fit-up gaps.

Moisture drains. Where feasible, low-point drains should be incorporated into the jacketing design to allow any water that does enter the system to escape rather than accumulating at the pipe surface. These are typically 1/4-inch diameter drain holes fitted with removable plugs or breathable membranes that permit liquid water egress while blocking water ingress. Drains are not universally applicable — they are contraindicated in fireproofing applications and where internal insulation contamination from external sources is a concern — but for above-ground process piping in temperate climates, they reduce CUI incidence measurably.

3c. Leachable Chloride Control: ASTM C795 and ASTM C871

For austenitic stainless steel piping and equipment, the chloride content of the insulation is a critical specification parameter. ASTM C795, "Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel," mandates that insulation materials undergo preproduction testing for stress corrosion cracking tendency per ASTM C692 and chemical analysis per ASTM C871.

ASTM C871, "Standard Test Methods for Chemical Analysis of Thermal Insulation Materials for Leachable Chloride, Fluoride, Silicate, and Sodium Ions," is the analytical method that quantifies water-extractable chloride, fluoride, silicate, and sodium content. The industry benchmark for austenitic stainless steel service is less than 50 ppm leachable chloride — a limit derived from field experience showing that Cl-SCC initiation risk rises measurably above this threshold when the metal surface temperature exceeds 140 degrees F (60 degrees C) and moisture is present.

The sodium plus silicate to chloride plus fluoride ratio, also determined by ASTM C871, is a secondary control parameter. Sodium and silicate ions act as SCC inhibitors by buffering the pH of any leachate and competing with chloride ions at the metal surface. A sodium + silicate to chloride + fluoride mass ratio exceeding 2:1 is considered protective; ratios below 1:1 warrant substitution with a low-chloride insulation grade.

ASTM C1617, "Standard Test Method for Quantitative Accelerated Laboratory Evaluation of Extraction Solutions Containing Ions Leached from Thermal Insulation on Aqueous Corrosion of Carbon Steel," provides a direct corrosion rate measurement. The test exposes carbon steel coupons to leachate extracted from the insulation material per ASTM C871 and measures mass loss over a prescribed exposure period. The resulting corrosion rate, expressed in mils per year (mpy), provides a comparative ranking of insulation material corrosivity that is more directly interpretable than ion concentration data alone.

4. Inspection and Detection Methods

Inspection for CUI is a tiered process: screening methods that detect moisture or wall loss without insulation removal, followed by direct examination where screening indicates elevated risk. The goal is to minimize the volume of insulation removed — at $50 to $150 per linear foot for removal, inspection, and re-insulation, stripping 100% of insulated piping at every turnaround is economically impractical — while maintaining acceptable probability of detection for damage exceeding the corrosion allowance.

Infrared Thermography (IRT). IRT is the most widely deployed CUI screening technique. Wet insulation has higher thermal conductivity and higher thermal mass than dry insulation. On a hot pipe, wet insulation conducts heat away from the pipe surface more efficiently, creating a cooler external surface that appears as a thermal anomaly on an infrared camera. On a cold or ambient-temperature pipe, wet insulation may appear warmer than dry insulation due to the higher heat capacity of water retaining solar gain. IRT sensitivity is highest when there is a significant temperature gradient between the pipe and ambient — at least 20 degrees F (11 degrees C) — and when the insulation surface is dry (wet jacketing masks the thermal signature of wet insulation beneath). Detection probability for wet insulation zones exceeds 80% under favorable conditions but drops below 50% in rain, high humidity, or when the pipe is offline.

Pulsed Eddy Current (PEC). PEC measures average wall thickness of ferromagnetic pipe through insulation and aluminum or stainless steel jacketing up to 4 inches (100 mm) thick, without requiring direct contact with the pipe surface. The technique induces eddy currents in the pipe wall using a pulsed magnetic field and measures the decay rate of the induced field, which is proportional to wall thickness. PEC provides an average wall thickness over the footprint of the probe (typically 2 to 6 inches in diameter), not a spot reading — it screens for generalized wall loss rather than isolated pitting. Detection sensitivity is approximately 10 to 15% wall loss for carbon steel pipe up to 0.5 inch (12.7 mm) nominal wall thickness, with accuracy decreasing for thicker walls and smaller diameters.

Visual Inspection and UT Thickness Mapping. Where IRT or PEC screening identifies a suspect location, controlled insulation removal followed by visual inspection and ultrasonic testing (UT) thickness mapping provides definitive assessment. Insulation is removed in 12 to 24 inch bands at flagged locations. The exposed surface is visually examined for corrosion product, pitting, and cracking, then grid-mapped with a digital UT gauge at 1 to 2 inch spacing to generate a wall thickness contour. Results are compared against nominal and minimum required thickness per the applicable piping code (ASME B31.3 for process piping, B31.1 for power piping).

Soluble Salt Testing. Before recoating any surface from which insulation has been removed, soluble salt contamination must be quantified. The Bresle patch method per ISO 8502-6 (extraction) and ISO 8502-9 (conductometric analysis) is the standard field technique. A self-adhesive patch creates a sealed chamber of known area (typically 1,250 mm²) on the blast-cleaned surface; deionized water is injected and extracted after a prescribed dwell time; the conductivity increase is measured and converted to surface salt density in mg/m² or micro-g/cm². For immersion-grade CUI coating systems, a limit of 20 mg/m² (2.0 micro-g/cm²) total soluble salts is a commonly applied threshold, consistent with NACE SP0198 recommendations for critical service.

5. Calcium Silicate's CUI Advantages

While the previous sections focus on managing CUI risk, calcium silicate insulation has several intrinsic properties that, when specified correctly, make it a defensible choice for CUI-managed systems.

XOX corrosion inhibitor technology. Modern calcium silicate formulations incorporate corrosion inhibitors during manufacture rather than as surface-applied post-treatments. These inhibitors — typically proprietary blends of inorganic phosphates, silicates, or molybdates — are distributed throughout the material matrix. When moisture contacts the insulation, the inhibitor dissolves into the aqueous phase and migrates to the pipe surface via the same capillary path that transports chlorides, forming a passivating film on the steel. Laboratory testing per ASTM C1617 shows mass loss corrosion rates for inhibitor-treated calcium silicate in the range of 2 to 5 mpy, compared to 15 to 30 mpy for untreated standard-grade material. The inhibitor is consumed over time as it reacts with incoming moisture, so the protection is not indefinite, but it provides a front-line defense during the interval between water ingress and discovery.

Low leachable chloride formulations. Calcium silicate can be manufactured with leachable chloride levels below 50 ppm, meeting ASTM C795 requirements for austenitic stainless steel contact. This is achieved through raw material selection — low-chloride quicklime and deionized process water — without altering the fundamental xonotlite chemistry or thermal performance. Standard grades typically run 100 to 500 ppm leachable chloride; low-chloride grades are a specified product variant, not a default property, and should be explicitly required in purchase specifications with mill test reports documenting ASTM C871 results per batch.

High compressive strength. Calcium silicate's compressive strength (2.5 to 13 MPa, or 360 to 1,890 psi, depending on density grade) maintains structural integrity over decades of thermal cycling. It does not sag, settle, or compress under its own weight on vertical surfaces, unlike mineral wool and ceramic fiber blankets which rely on wire pins and mesh for retention. This dimensional stability eliminates one CUI initiation mechanism: gaps that form when fibrous insulation compacts under cycling, creating uninsulated cold spots that condense moisture and pipe-to-insulation crevices that trap water. The rigid board resists mechanical damage from foot traffic during maintenance better than compressible materials, preserving the vapor barrier continuity.

pH-neutral formulations. Standard-grade calcium silicate is mildly alkaline (pH 9 to 11 in aqueous slurry), which is protective for carbon steel — the passive iron oxide film is stable in alkaline conditions. This contrasts with some mineral wool products that incorporate acidic phenolic resin binders; binder degradation products can acidify trapped moisture. Formulations that maintain a leachate pH above 8.5 avoid the acid-attack mechanism documented in field CUI investigations where low-pH leachate accelerated general corrosion rates.

ASTM C1617 testing availability. Calcium silicate manufacturers can provide ASTM C1617 corrosion rate data, enabling direct quantitative comparison of corrosivity between material grades and between suppliers. This test goes beyond ion concentration analysis to measure the actual corrosion response of steel to the total leachate chemistry, including the effects of inhibitors, pH, and synergistic ion interactions that are invisible to compositional analysis alone. When specifying calcium silicate for CUI-sensitive applications, requesting ASTM C1617 test reports alongside ASTM C871 chemical analysis provides a more complete picture of long-term corrosion risk.

6. When to Replace vs Repair

When CUI is discovered during an inspection, the decision between repairing the existing pipe and replacing affected sections is both an engineering and an economic judgment. The following framework is based on industry practice for process piping operating under ASME B31.3.

Repair is appropriate when:

• Corrosion is limited to the external surface with no indication of internal wall loss.
• Maximum pit depth is less than 50% of the corrosion allowance as defined in the piping specification.
• Remaining wall thickness after blast cleaning exceeds the minimum required thickness per ASME B31.3 (t_min = PD / (2(SE + PY)) for straight pipe under internal pressure, where P is design pressure, D is outside diameter, S is allowable stress, E is joint efficiency, and Y is the temperature coefficient).
• No stress corrosion cracking is detected on stainless steel components by liquid penetrant testing of welds and heat-affected zones.
• The corroded area is accessible for surface preparation and coating application without disassembly of adjacent piping.

Repair procedure: Remove insulation a minimum of 12 inches beyond visible corrosion. Blast clean the affected area to SSPC-SP10 (near-white metal) with a surface profile of 2 to 3 mils (50 to 75 microns). Test soluble salt levels via Bresle method (ISO 8502-6/9); if results exceed 20 mg/m², re-blast or wash with deionized water until the limit is met. Apply the specified immersion-grade coating system per NACE SP0198, extending the coating a minimum of 4 inches beyond the blast-cleaned area onto intact existing coating. Verify DFT with a calibrated gauge. Re-insulate using new calcium silicate sections (do not re-use removed insulation) with new jacketing and sealed terminations.

Replacement is required when:

• Deep pitting exceeds the corrosion allowance and remaining wall thickness is below minimum required thickness.
• Wall loss is generalized (not isolated pitting) over a length exceeding 12 inches or spanning a circumferential arc greater than 90 degrees.
• Stress corrosion cracking is confirmed on austenitic stainless steel by metallurgical evaluation — liquid penetrant testing followed by metallographic sectioning of suspect indications.
• Fitness-for-service assessment per API 579-1/ASME FFS-1 determines that the damaged section does not meet Level 1 or Level 2 acceptance criteria for continued operation.
• The pipe material is at the end of its design life based on corrosion rate data and the planned interval to the next scheduled turnaround.

Consider hydrophobic alternatives for chronic CUI locations. Piping locations that have experienced repeat CUI — defined as requiring repair at two or more consecutive turnarounds despite standard coating and installation practice — should be evaluated for material substitution. Hydrophobic insulation materials, such as silica aerogel blanket (thermal conductivity 0.012 to 0.015 W/m-K at ambient temperature), are intrinsically water-repellent and do not wick liquid water. Their installed cost per linear foot runs higher than calcium silicate, but the cost comparison against repeat CUI repair at each turnaround cycle may favor substitution for the specific high-risk locations. The analysis should be location-specific: running a different insulation material on a single problematic pipe run adds procurement and installation complexity, so the economic threshold for substitution requires documented repeat-failure history.

7. CUI Prevention Best Practices Checklist

The following eight items constitute a minimum CUI prevention program for calcium silicate-insulated piping and equipment. Each item references the applicable standard or guidance document.

1. Coating selection. Select an immersion-grade coating system per NACE SP0198-2010 appropriate for the full operating temperature range, including shutdown. Verify the coating manufacturer's documented service temperature range against process data. For stainless steel, specify coating per NACE SP0198 Section 5.
2. Chloride testing. Specify ASTM C795-compliant calcium silicate for austenitic stainless steel service. Require batch-specific ASTM C871 test reports showing leachable chloride below 50 ppm. For carbon steel, request ASTM C1617 corrosion rate data to compare insulation grades.
3. Vapor barrier. Install continuous metallic jacketing with minimum 2-inch overlaps, seams at 4/8 o'clock positions, and stainless steel bands at 12-inch maximum spacing. Use 304 stainless steel jacketing in marine or cooling tower drift environments where aluminum corrodes.
4. Proper installation. Seal all terminations with vapor-stop mastic extending 2 inches beyond the insulation cut line. Use pre-formed termination shields at flanges and valves. Install insulation dry — do not apply to wet or rain-exposed pipe.
5. Drainage design. Incorporate low-point drains in horizontal pipe runs where process conditions permit. Ensure drain holes are oriented downward and fitted with removable plugs. Verify that drain locations are accessible for inspection.
6. Inspection schedule. Implement a risk-based inspection program per API RP 583. Screen with IRT at each turnaround for all insulated piping within the CUI temperature range. Apply PEC at locations with damaged jacketing, known leak history, or CUI-susceptible geometry (dead legs, supports, low points).
7. Documentation. Maintain a CUI inspection database recording location, insulation type, coating system, inspection date, method, findings, and repair action for each inspection point. Use this data to trend corrosion rates and adjust inspection intervals per API RP 580 risk-based inspection methodology.
8. Training. Ensure insulation installers, coating applicators, and NDT technicians are qualified to the relevant standards. Coating applicators to NACE No. 13/SSPC ACS-1. Insulation installers to a recognized training program with demonstrated competency in vapor barrier installation. NDT technicians to ASNT SNT-TC-1A Level II in the applicable method.

8. Frequently Asked Questions

References and Further Reading

• NACE SP0198-2010. Control of Corrosion Under Thermal Insulation and Fireproofing Materials — A Systems Approach. NACE International, 2010.
• ASTM C795-08(2023). Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel. ASTM International.
• ASTM C871-18(2023). Standard Test Methods for Chemical Analysis of Thermal Insulation Materials for Leachable Chloride, Fluoride, Silicate, and Sodium Ions. ASTM International.
• ASTM C1617-19. Standard Test Method for Quantitative Accelerated Laboratory Evaluation of Extraction Solutions Containing Ions Leached from Thermal Insulation on Aqueous Corrosion of Carbon Steel. ASTM International.
• API RP 583. Corrosion Under Insulation and Fireproofing. American Petroleum Institute, 2021.
• API 579-1/ASME FFS-1. Fitness-for-Service. American Petroleum Institute / American Society of Mechanical Engineers, 2021.
• ISO 8502-6:2020. Preparation of Steel Substrates Before Application of Paints and Related Products — Tests for the Assessment of Surface Cleanliness — Part 6: Extraction of Soluble Contaminants for Analysis — The Bresle Method.
• ISO 8502-9:2020. Preparation of Steel Substrates Before Application of Paints and Related Products — Tests for the Assessment of Surface Cleanliness — Part 9: Field Method for the Conductometric Determination of Water-Soluble Salts.
• SSPC-SP10/NACE No. 2. Near-White Metal Blast Cleaning. SSPC/NACE Joint Standard.
• Elban, W.H. and Winnik, S. "Inspection Techniques for CUI: Capabilities and Limitations." NACE Corrosion 2016 Conference Paper No. 7368.
• De Vogelaere, M. et al. "Pulsed Eddy Current: A Proven Tool for CUI Detection." NACE Corrosion 2020 Conference Paper No. 14772.
• Mingfa Calcium Silicate Pipe Insulation — Pre-Formed Half Shells and Sectional Pipe Covering
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