Best Practices in Installing Process Vessel Lining Systems
Managing internal erosion and corrosion of process vessels under arduous service environments is a challenging task. This article explores best practices in installing epoxy lining technologies to minimize the risk of poor application standards.
A lining solution can only be an effective and integral part of the corrosion prevention system if installed correctly. Unintentional mistakes or short cuts taken during the application can have a significant effect on the project cost, lead-time, quality, and the long-term performance of the lining.
Once the lining system is chosen, the vessel should be designed for lining applications in the case of new builds. It is important that the vessel designer and fabricators liaise with the lining manufacturer when possible, ideally prior to completion of the design phase to ensure that the vessel will be designed for the application of a lining system. (Learn more about proper design in the article How to Control Corrosion by Improving Design.)
Poor vessel design can render a vessel or piece of equipment difficult to line, which can lead to potential lining failures associated with misses and poor surface preparation. Some examples include the following:
- Nozzles of small diameter, typically less than 4 inch (102 mm), are difficult to be properly surface-prepared and lined via manual application
- Excessive amounts of internal pipework running in multiple directions can complicate the application process
- Inaccessible boot areas that make the lining inspection process difficult
- Welded internal furniture limiting access to the vessel
All of these design problems may not necessarily be well known by vessel designers, and as such, not be considered “problems.” This is why, once a lining option has been chosen as an integral part of the corrosion prevention system, vessel designers should include the lining manufacturer in the design process and allow them to review, comment and even sign off on final designs before fabrication.
By doing so, nozzles of small diameter can be lined with a custom-built polymer sleeve, fabricated of a corrosion resistant alloy or larger diameter nozzles can be specified.
Application standards-validated training has been introduced by several lining manufacturers in response to many global clients’ requests to address the increasing risks to all parties (global client asset owners, engineering and application contractors and lining manufacturers) associated with poor application standards of lining materials resulting in premature failure.
Nowadays, many of these parties specify the mandatory requirement for competent applicators with demonstrable training and application experience associated with specific manufacturing materials. Properly trained applicators must also provide certification and validation training records, preferably directly from the lining manufacturer.
The value to the asset owner or operator of using validated applicators and directly involving the product’s manufacturer is a demonstrable reduction in the application risk that improves the lining system’s life. This practice can also significantly increase asset reliability, operational time on line, and hence business bottom-line commercial performance.
The value to application contractors in becoming validated applicators is the potential increase in business opportunity, particularly as more asset owners and clients are moving toward the exclusive use of validated applicators.
At least one lining manufacturer has been contacted by global clients to train and validate applicators on material selection, surface preparation standards, climate control and vessel lining via manual and spray techniques. Training shall include theoretical and practical sessions. The trainees shall be tested in their theoretical knowledge and workmanship.
Supervision of Lining Application Projects
Lining application projects should be monitored by qualified coating inspectors (e.g., FROSIO, NACE or equivalent) who can witness and record the achievement of the specification requirements on the quality control documentation. These inspectors shall also have a clear understanding of the application techniques as recommended by the lining manufacturers.
An experienced supervisor who is familiar with the lining product and vessel lining application project delivery can prove to be invaluable in maintaining the project timeline and keeping it on budget.
Application Quality Control
Quality control management is a paramount step to deliver a successful lining application. It implies establishing a set of control measurements to ensure the project achieves an acceptable outcome. (Discover the basics in What is Quality Control?) To manage the quality of an application, several hold points must be set forth.
Hold points are certain points in the application where inspection must be carried out to determine if the application is proceeding as per specification. Upon reaching these points, the application must be held off from continuing until compliance is confirmed and signed off on the quality control (QC) documentation.
Some hold points within the application procedure are associated with the surface preparation process. The ultimate adhesion of the lining to the substrate will be wholly dependent upon the achievement of the surface preparation standards specified in terms of surface cleanliness.
Acceptable cleanliness levels for vessel linings include NACE 2/SSPC SP101 or NACE 1/SSPC-SP52 with an irregular average profile depth of at least 3 mils (75 microns). The verification of the surface preparation specification must be measured and recorded in the QC documentation using appropriate internationally recognized procedures as those described by NACE RP0287.3
In addition to the surface cleanliness of the steel substrate, the levels of internal contamination must also be measured to demonstrate compliance to the specification. The contaminants are typically soluble salts embedded in the substrate. The removal or reduction of the salts to below the specified maximum level is vital to prevent osmotic processes from affecting the long-term performance of the lining. These maximum levels are typically specified by the asset owner and the lining manufacturer.
It is possible that at times the maximum acceptable levels provided by the asset owner are greater than those recommended by the lining manufacturer, in which case both parties should discuss and agree on the actions moving forward. The inspection procedure described by ISO 8502-54 and ISO8502-65 can be employed to measure the substrate soluble contamination level.
Environmental control during surface preparation, application and curing is another critical part of the process. Typical environmental conditions to manage include relative humidity, substrate temperature and air temperature close to the substrate. It is generally recognized that the difference between the dew point and surface temperature must be greater than 5°F (3°C) for equivalent rust bloom protection. NACE 6A192/SSP-TR36 provides detailed information about why and how dehumidification and temperature control can be effectively used to achieve higher quality lining applications.
Once applied to the surface, the lining integrity must be checked visually and by using appropriate inspection equipment to check for defects (holidays or pinholes). Procedure described by NACE SP01887 should be followed. Likewise, the total dry lining thickness must be quantitatively assessed to ensure that the minimum and maximum average measurements are not below or above specified minimum and maximum thicknesses, respectively. Internationally recognized inspection techniques described in SSPC PA 28 should be followed. Any defects or areas below or above the specified thickness limits may compromise the lining and lead to premature failure when the vessel is in operation.
No project runs perfectly. Situations arise that require deviations or a non-conformance to the specification. A non-conformance indicates a problem that should be addressed with corrective action. It is a sign that some steps of the lining application process did not meet the specification due to local circumstances.
All the aforementioned hold points can constitute non-compliance if corrective actions are not taken and the application proceeds. A non-conformance can be identified via inspections prior, during and after completion of a lining application. The procedure should include immediate actions to stop further non-conformance. In these cases, a noncompliance report must be logged that, at a minimum, includes the following details:
- Name of project and vessel number
- Clear description of the non-conformance
- Details of the companies involved with the non-conformance including the company writing the non-conformance, the affected company and the company responsible for correcting the non-conformance
- Suggestive corrective actions to be taken
- Clear description of the corrective actions actually taken
- Signatures of all parties involved in the lining application work
Provided that quick informed decisions are made at the site through effective communication between all the parties involved in the project, these deviations should not adversely affect the project schedule.
Asset owners and operators in the oil and gas industry are always very concerned about the life cycle costs of installing and managing lining corrosion protection strategies. The main problem is that maintaining a vessel upon completion of the lining process implies shutting down the whole plant process or part of it, steaming out or chemically cleaning the vessel and inspecting the vessel after access is gained.
The costs associated with maintenance shutdown and start-up, just to cite a few, is enormous. Several conversations between the author and asset owners have revealed that their actual inquiry is this: “How can I ensure the lining remains in good condition after installation without gaining access to the vessel for inspection purposes?”
It is the opinion of the author that the corrosion strategy should include regular non-destructive testing (NDT) from the outside of the vessel for directly monitoring any further damage or to indirectly monitor conditions that might lead to further damages. Although such NDT readings do not provide details regarding the condition of the linings, they can be progressively taken and comparatively analyzed.
For example, if a point wall thickness reading taken one year after the vessel was lined shows no difference from the same point measurement taken before the vessel was lined, that is a qualitative indicator that the lining is still protecting the wall from the surrounding environment. This type of in-service monitoring prevents the need for unnecessary shutdown and start-up procedures and the excessive associated costs.
There is a need for further development of NDT technologies to enable on-line monitoring of the lining and its bonding to the substrate via external inspection techniques. This would definitely add value to the use of lining alternatives as an integral part of any corrosion prevention programs.
In conclusion, there are numerous strategies to manage erosion and corrosion and maintain the integrity of process equipment during its design life. Ultimately the system selected by the equipment owner should offer the following benefits:
- Lower maintenance costs, reduced downtime
- Improved efficiency and safety
- Simple maintenance procedures
- Extended machinery and equipment design life
Vessels can be lined for protection against corrosion and erosion. Where the operating conditions permit and the correct procedures are followed, advanced organic linings can offer all the above benefits, thereby significantly reducing the life cycle cost of the asset.
Linings can be subjected to pre-qualification tests to provide demonstrable evidence of their fitness for service in the oil and gas industry. The application of a lining solution is a critical stage in its delivery.
By training the application contracting company in the use of best application techniques, using certified supervision and implementing quality control procedures during the application, application risks can be reduced, increasing the asset’s reliability, operational on-line time, and successful performance.
- NACE No. 2/SSPC-SP 10, “Near-White Metal Blast Cleaning” (Houston, TX: NACE International).
- NACE No. 1/SSPC-SP5, “White Metal Blast Cleaning” (Houston, TX: NACE International).
- NACE RP0287-2002, “Field Measurement of Surface Profile of Abrasive Blast-Cleaned Steel Surfaces Using a Replica Tape” (Houston, TX: NACE International).
- ISO 8502-5:1998, “Preparation of Steel Substrates before Application of Paints and Related Products – Tests for the Assessment of Surface Cleanliness – Part 5: Measurement of Chloride on Steel Surfaces Prepared for Painting (Ion Detection Tube Method)” (Geneva, Switzerland: ISO).
- ISO 8502-6:2006, “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” (Geneva, Switzerland: ISO).
- NACE 6A192/SSPC-TR3, “Dehumidification and Temperature Control During Surface Preparation, Application, and Curing for Coatings/Linings of Steel Vessels, and Other Enclosed Spaces” (Houston, TX: NACE International).
- NACE SP0188-2006, (formerly RP0188) “Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates” (Houston, TX: NACE International).
- SSPC PA 2, “Procedure for Determining Conformance to Dry Coating Thickness Requirements” (Pittsburgh, PA: SSPC).