Corrosion Under Insulation and Fire Proofing Materials V. P. Sastry TCR Arabia Company Ltd.

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1 Corrosion Under Insulation and Fire Proofing Materials V. P. Sastry TCR Arabia Company Ltd. Tel: /85 Seventh Middle East NDT Conference & Exhibition 2015, Bahrain Sept,, 2015

2 Introduction External corrosion under insulation (CuI) or Corrosion under Thermal Insulation (CuTI) of insulated piping, equipment and structural components is experienced worldwide, mainly due to the entry of water /oxygen. Noticed in both cold and hot insulated systems as well as in fire proofed systems-corrosion under Fire Proofing (CuFP). Can not be noticed as the process is behind the insulation / fire proofing.

3 Introduction Moisture into the insulation system may further Carry the air borne pollutants/corrosive substances Water leaches out chlorides, other halides or sulphates leading to corrosion. Punctures, slipped cladding, seal deterioration aid the easy entry of water into the insulation. Render the insulation ineffective. For example,1 vol.-% of water in the insulation material leads to an approximate 4% increase in the thermal conductivity. A water concentration of 5 vol.-% of the overall insulation material s volume, increases the l value by 20%.

4 Influencing factors Design specifications-to define all the measures for good quality water tight insulated/fire proofed systems. Installation craftsmanship, and maintenance-less attention paid by the owner users in terms of supervision. Openings thru. Insulation cladding for many reasons like poor workmanship, misuse, deterioration of sealing materials. Presence of moisture or water, oxygen, chloride ions and other salts, chemical contamination like acids, acidic gases, alkalis, salts... in a process plant situation, many such possibilities may arise. Warm temperatures...this depends up on location. Abuse of insulation of insulated system- walking on the insulated lines, misuse of lifting tools and tackles during maintenance.

5 Susceptible areas for CUI: Specific locations and / or systems penetrations in the insulation and visually damaged insulation areas. Environmental or surrounding areas include: Insulated Carbon steel and low alloy systems, operating temperatures between - 5 C and 150 C, frequent or continuous condensation and re-evaporation of atmospheric moisture, systems normally operate above 150 C but are in Cyclic thermal/ intermittent service or subjected to frequent outages. Susceptible temperature range for Stainless Steels is 65 to 204 deg.c. Carbon Steels /Alloy Steels show pitting/loss of thickness, Stainless Steels show pitting, SCC in Chloride contamination. Areas exposed to mist over spray from cooling towers, steam vents, fire water spray systems, deluge systems, areas subject to process spills, ingress of moisture, or acid vapors. Protruding dead legs and attachments, Vibrating systems may loosen the insulation cladding joints, Steam tracing leaks beneath the insulation, Systems with deteriorated coating and/or wrappings, Cold service operating below the atmospheric dew point. Weather Proofing/Mastic Wraps Some of these are covered in case studies.

6 Cold/hot thermal insulation and components: Some of the insulation components inherently cause problem unless enough care is taken. Cladding- It protects the insulated pipe/equipment. Cladding joints form the basis for the leaks into the insulation through any openings. The cladding joint foil many a time creates gap due to wavy stiff end, without closely touching the mating surfaces. Cladding joint sealing materials- some of the sealing materials lose the sealing property over a period of time due to weathering/deterioration. Asbestos felt sealing may not be adequate. Screws-the screwed points are also a potential source for water ingress into the insulation. Some of these screws may seen missing in plant visual audit round. Fiber/powder based insulations retain water. Insulation materials such as mineral wool, glass wool and Ca silicate have some chloride and other salt contamination. Water leaches out these soluble salts from insulation. Vapor retarder, Insulation bonding agents

7 Prevention Design aspects specification is the key to cover all the design aspects of Insulation Materials, cladding, Heat-traced Systems, Protective Coatings and sealing, Shutdown/Mothballing, Quality Control/Quality Assurance and follow. Some examples include: Avoid creating inspection ports. Select where possible insulation systems like Foam glass which hold less water. Old specifications did not call for protective coatings on the pipe/equipment/structural, before applying the insulation. Use coatings to prevent corrosion due to the entry of moisture. CuTI resistant coatings are required for both cold and hot insulation7. Coatings for systems without insulation may not work for systems with insulation

8 Inspection One of the important inspection requirements is to get the metal loss due to CuTI. For this first initial thickness is required. Baseline surveys are best carried out during the construction phase, before applying coating and insulation. This helps in taking corrective actions for components not meeting the specification can be readily done. CuTI is difficult to identify and hence where to start is important. An account of susceptible areas can be used as a guide. Insulated systems are to be reviewed to identify periodic inspection for critical areas to take corrective actions. The review is based on the process and mechanical data. Where possible, remove the insulation on the critical areas for inspection.

9 Inspection DP, Ultrasonic thickness measurements are commonly used, where the insulation is removed. In addition, advanced NDT is also required. For CuTI inspection, Visual examination (for all cases of without/local/full removal of insulation) helps in eliminating misinterpretation with other NDT. If inspection program is planned for multi plant complex, number of insulated lines may be at least one lakh in addition to thousands of equipment. Removing insulation of all these lines even in small lengths, for inspection, would be highly laborious, time taking and cost intensive.

10 Inspection Large lengths of insulation removal mean that there is a maximum possibility of affecting the process. This restricts the inspection rate. Cryogenic insulation removal is not advisable during operation due to ice formation. Hence, techniques to predict the condition of metal beneath the insulation are required without its removal.

Advance NDT : Thermography It is important to inspect insulated pipe work, equipment and structural to identify CuTI/CuFP sites. One can detect hot/cold spots with at least 10 deg.

11 Advance NDT : Thermography It is important to inspect insulated pipe work, equipment and structural to identify CuTI/CuFP sites. One can detect hot/cold spots with at least 10 deg. C temperature differential across the thickness of the Component. It is a remote condition monitoring technique which identifies the presence of moisture through mapped surface temperatures. For some field applications, consider influencing factors such as changes in surface Emissivity, the affects of sunlight heat and other atmospheric effects. Ideally, Thermography should be done before rainy season and repeat at the end of the season and correlate. Thermogram of carbon steel insulated line, showing wet patch

12 Advance NDT : Profile Radiography This technique is used in the plant inspection. Where the process plants use nucleonic gauges, the radiography source radiation interferes with the nucleonic gauge radiation and plants may trip. This problem becomes acute when the plants are adjacent to each other. Also it is a slow technique when many lines are to be done. Taking profile at multiple different angles is useful to catch the area of Interest. Profile radiography to check the wall loss

The amount of radiation received by detector (figure) is converted to an equivalent steel thickness measurement by the instrumentation.

13 Advance NDT : Lixi Profile Lixi profiler, a portable battery operated unit as shown in (figure), uses Gd153 radioisotope source. When detector assembly is placed around pipe, small amount of focused radiation beam penetrates the diameter of the pipe. The amount of radiation received by detector (figure) is converted to an equivalent steel thickness measurement by the instrumentation. Variation in density (thickness) is plotted on a computer screen in real time image. 1. Computer module 2. Uniconnect module 3. Detector module 4.HUD 5. C-Arm Source holder 7. Battery brick

14 Advance NDT : Lixi Profile Applications of Lixi Profiler include: Pipe wall thinning, Corrosion under Insulation (CUI, Pipe Blockages such as Bitumen, Ice, or any another foreign material Wet Insulation Cluster of Internal and external pitting, Wall thickness measurement on insulated or bare pipes w/ or w/o product, Wall thickness measurement on very hot pipes while inservice, Weld Identification on Insulated Piping Systems. The profiler can be used on hot permit system.

15 Typical plot for a corroded insulated pipe

Guided Wave Inspection Ultrasonic screening in-service inspection tool to detect general corrosion and wall loss for 100-150

(a) Instrumentation (b) Probe mounting on a small length of pipe where insulation is removed. It is effective for T< 120 deg.

16 Guided Wave Inspection Ultrasonic screening in-service inspection tool to detect general corrosion and wall loss for ft. on either side of the probe. Ultrasonic wave guide for CuTI inspection. (a) Instrumentation (b) Probe mounting on a small length of pipe where insulation is removed. It is effective for T< 120 deg.c. Operator skill is needed. May not detect defects in immediate vicinity of welds. Reliability decreases with length. Signal will terminate at a flange or at second elbow.

17 Advance NDT : Pulsed Eddy Current (PEC) PEC is a noncontact type inspection technique for carbon steel objects, such as pipes and vessels. It can measure % variations in steel thickness through any nonconductive and non-magnetic material between sensor and steel surface such as air, insulation material, concrete, plastics, coatings, paint, sea water, marine growth deposits, oil etc. Electrical current flows through the transmitter coils of probe and generate a primary magnetic field. This field is unaffected by the presence of any non-conducting and non-magnetic material and penetrates undisturbed and magnetizes the top layer of the steel beneath the transmitter coils.

18 Advance NDT : Pulsed Eddy Current (PEC) 1. Magnetization of the Steel 2. Induced eddy currents Generate secondary magnetic field in the receiver coil 3. Diffusion of eddy currents. Onset of fast decay occurs when far surface is reached.

19 Advance NDT : Pulsed Eddy Current (PEC) The current in the transmitter coil is switched off, collapsing the primary magnetic field. The changing magnetic field induces electrical eddy currents in the surface of the steel. These eddy currents generate a secondary magnetic field and induces an electrical voltage, which in the receiver coils. The magnitude of this voltage as a function of the time is referred to as the PEC signal. The PEC signal contains information about the thickness of the steel, as described below. A specimen has a near and a far surface. Initially the eddy currents are confined to the near surface (closest to the PEC probe) but, as time elapses, they travel (or diffuse ) outwards towards the far surface (figure 9). As long as the eddy currents experience free expansion in the wall, their strength decreases relatively slowly.

20 Advance NDT : Pulsed Eddy Current (PEC) However, upon reaching the far surface, their strength decreases rapidly. The moment in time where the eddy currents first reach the far surface is indicated by a sharp decrease in PEC signal, known as transition point (figure 9). The time of the transition point is therefore a measure of wall thickness. For example, the earlier the transition point, the sooner the eddy currents reach the far surface and the thinner the wall must be. In practice, each time a PEC measurement is done; voltage across the receiver coils of the PEC probe is amplified, sampled and digitized by the PEC instrument. This gives a digital record of the PEC signal over 3000 sample moments in time. The digitized signals are stored in a connected computer. Dedicated software is used to analyze the shape of all PEC signals and thereby determine wall thickness.

21 Remaining wall thickness of one leg of Horton sphere Colour code: 85-90%; % Circumferential position at 90 degrees Top side end Vertical Position A B C D Distance between two points is 0.1m Distance between two points is 0.5m Ground side end

22 Case Studies Examples of reasons for CuTI experienced, measures taken. Inadequate design aspects Normally Stiffening rings, platform support rings and Insulated support rings are not provided with drain holes for possible collection of rain water on to the rings. Hence corrosion is often vulnerable. Connected to the process columns operating temperature between 60 to 100 deg.c due to accumulation of Water in the mineral wool insulation support ring. As a corrective action, holes are drilled; apply suitable paint to resist under insulation corrosion applied. Update the specification. Column ring without holes causing corrosion due to accumulation of water in rainy season.

23 Fire proof insulation: In the process column, bottom piping leaked exactly where the pipes crossing the fire proofed skirt, due to long contact with water beneath the fire proofing. Specification is updated to do CuTI paint before fire proofing. Leakage of column bottom pipes in contact with column skirt fire proofing

24 12 O clock clad joints To protect water entry, the clad joints shall be at 6 O clock position The clad joints shown with Arrow in 1 O clock/12 O clock poisons. These should have been at 6 O clock position to avoid direct water entry through the joint gaps. Update the specification.

Deviation from design conditions Different Normally No Flow (NNF) hydrocarbon carbon steel lines or dead legs of varied diameters are hot mineral wool insulated expecting above ambient temperatures.

All such affected lines are replaced with new lines and CuTI resistant paint was applied before insulation. But these lines did not have any flow, experienced only ambient temperatures.

25 Deviation from design conditions Different Normally No Flow (NNF) hydrocarbon carbon steel lines or dead legs of varied diameters are hot mineral wool insulated expecting above ambient temperatures. But these lines did not have any flow, experienced only ambient temperatures. Pipe wall thinning as much as 50% in 15 years of time under insulation. All such affected lines are replaced with new lines and CuTI resistant paint was applied before insulation. But these lines did not have any flow, experienced only ambient temperatures. One such PSV upstream line was mineral wool insulated as per Line Designation Table (LDT), but remained at ambient temperature. Mineral wool insulated lines as per LDT but remained at ambient T-used intermittently during plant shutdowns, for commissioning/ decommissioning. CuTI on intermittent service line Corroded insulated PSV upstream line due to ambient temperature

26 Heat traced lines to maintain the liquid temperature and hence insulation was used. Electrical heat traced lines, found corroded in-service. These lines were audited/reassessed and found that the tracing is not required. So the electrical tracing was disabled. So this 2, Sch. 40 Carbon steel line carrying fuel gas experienced ambient temperatures leading to corrosion under mineral wool insulation. Remedial action done included replacing the corroded length, removal of heat tracing and application Paint to resist Corrosion under Insulation. Insulation removed for inspection. Electrical heat tracing is disabled. Corrosion noticed under insulation.

40 carbon steel lines for benzene service.

27 Similarly Steam tracing line leaked and corroded the pipe under mineral wool insulation as steam tracing is not activated on 6 Sch. 40 carbon steel lines for benzene service. CuTI on steam tracing inactivated line Abuse of insulated lines as some personnel walk on them

28 Corroded cladding Direct water entry is possible through the cladding damages. Corroded insulation cladding. GI sheet performs poorly as a cladding material.

29 Cladding joints sealing material life. Sealing material works for some time. After that, due to dry up cracks or fall off, the joints are exposed. Well before monsoon, these joints are to be inspected and rectified in the problem areas. Another problem noticed is that the cladding ends should not have wavy pattern to have proper sealing. If found, they have to be smoothened / straightened. Clad joint sealant with proper sealing Clad sealing. Mark 1 is the asbestos sealant and Mark 2 shows the absence of sealing on top allowing the possibility of any contamination / ingression.

30 Exposed insulation Exposed insulation at the ends of the lines, supports etc. due to improper or incomplete or no cladding Incomplete installation of insulation. Incomplete provision of insulation. Cladding cover is missing.

Influence of neighboring plants. Insulated Stainless steel type 304 lines are vulnerable for cracking. Make up water to De-aerator T 60 deg.c. These lines are prone to failures as exposed to neighboring continuous plume from cooling tower fan exhaust and steam leakages and contamination.

31 Influence of neighboring plants. Insulated Stainless steel type 304 lines are vulnerable for cracking. Make up water to De-aerator T 60 deg.c. These lines are prone to failures as exposed to neighboring continuous plume from cooling tower fan exhaust and steam leakages and contamination. Corroded lines were replaced and provided with SS foil before insulation. SCC on stainless steel line

Leakage of steam tracing leaks External corrosion of a pipe

redone during maintenance Improperly done cladding.

32 Leakage of steam tracing leaks External corrosion of a pipe and flange joint / fasteners at the break of mineral insulation due to leaky steam tracing. Maintenance Insulation and cladding improperly done / not redone during maintenance Improperly done cladding. No sealing also for clad joints Inadequacy in Insulation of Piping supports CuTI Deposits in the Support Lugs

Corrosion of piping supports Piping support corrosion is a frequently noticed problem under insulation. They have to be inspected closely and take corrective actions.

33 Corrosion of piping supports Piping support corrosion is a frequently noticed problem under insulation. They have to be inspected closely and take corrective actions. In case of new plants, adequate focus has to be given in specification preparation to minimize the problem. In the field, they have to be maintained with a close watch. Another example of corrosion under insulation of a 2" carbon steel pipe near bottom welded support. The support pipe covered under the piping insulation is also found corroded and perforated.

34 a) Open inspection pocket b) Improperly fitted Inspection pocket RECOMMENDATIONS: Insulation system is designed and done as per international norms, codes and standards. Learn from others problems, conduct necessary audits and take precautions by the owner users for the assets.

35 Recommendations Insulation system is designed and done as per international norms, codes and standards. Learn from others problems, conduct necessary audits and take precautions by the owner users for the assets.

36 Acknowledgments The author thanks the organizers for accepting the paper for presentation.

CUI (CORROSION UNDER INSULATION) MECHANISM THEORY AND PRACTICE

CUI (CORROSION UNDER INSULATION) MECHANISM THEORY AND PRACTICE Prepared By: Mohammed AbuALRub SAFCO Reliability Dept. December 10, 2015 CONTENT Introduction CUI PhenomenaMain components of the cold insulation