PROCEDURES

What Advance Preparation Is Necessary Before Going Out To Inspect Coating Or Lining Work? The inspector of the painting of some equipment in...

What Advance Preparation Is Necessary Before Going Out To Inspect Coating Or Lining Work?

The inspector of the painting of some equipment in a fabrication shop may not be as complex an activity as the inspection of the lining of the containment vessel in a nuclear power facility; however, the same basic principles will apply.

The inspection of any coating or lining system should be a planned function. Before the inspector goes out to inspect coating or lining work, the following preparations is necessary:

• Assemble and study al pertinent documents

• Verify that all the required instruments are available

• Organise an inspection plan

What Types Of Documents Should Be Assembled And Studied?

The inspector should familiarise himself with the surface preparation and coating or lining application requirements, and the characterised of the material being applied. The following documents should be assembled and thoroughly studied.

• Specifications(including all amendments and pertinent appendices)

• Applicable codes and standards

• Manufacturer’s published instructions

• Suppliers coating or lining procedures.

What Equipment Us Required To Perform An Inspection?

The specifications will define the required inspection tests and the acceptable instruments for the performing the inspection. Depending upon the materials being applied, the specifications requirements may very from one coatings inspection to another. The following is a list of the most frequently inspection instruments.

• Pictorial surface preparation standards (SSPC – VIS 1 or accepted euqal)

• Surface profile with psychrometric charts or tables.

• Thermometers – air and surface temperature

• Gauges – dry film with calibration standards or shims; wet film thickness.

• Tooke gage

• Flashlight and pocket magnifier

• Holiday detector 

• adhesion tester

What Is the Importance of Organising an Inspection Plan?

An inspection plan allows the inspector to organise, in a chronological sequence, the inspection activities he is required to perform. On some projects, inspection plans are mandatory and are already planned function for the inspector. However, if an inspection plan is not mandatory and has not been furnished, the inspector should prepare his own inspection plan. An organised inspection plan, even for the smallest job, will make one a more efficient inspector.

What Type of Information Should be Included In an Inspection Plan?

The information that should be included in an inspection plan will vary depending on the material being applied and the nature of the work. The following is information that should be included in every inspection plan:

• inspection plans

• codes, standards, specifications and procedures

• surface preparation inspection

• final applied coating inspection

What Inspection (Hold) Should Be Included In The Inspection Plan?

As discussed above, the inspection (hold) points will be depend upon the coating and lining material applied and the type and nature of the work. The inspection points listed below should be considered as basic for the most work; however, additional inspection points may be added if necessary.

• Prior to the start of the work

• Immediately following the surface preparation

• Immediately prior to the coating or lining applications

• Following the application of each coat

• Following the curing of the coating or lining.

• Final inspection and sign-off, in accordance with the project requirements.

What Should Be Inspection Activities At These Inspection Points Included?

• The first inspection (hold) point should follow the pre-surface preparation inspection, during which the supplier will have identified grease of oil deposits, metal imperfections (such as scabs, delimination, and metal damage), inaccessible areas and so forth. Dew points and surface temperature readings should be taken just prior to allowing surface preparations to proceed.

• An inspection (hold) point following the completion of surface preparation is mandatory. This will verify that the degree of cleanliness specified has been achieved according to the definition of the SSPC standard specified and that the required profile has been created.

• The inspection (hold) point prior to the coating or lining applied would be a repetition of the previous inspection point; however; this inspection point is established to make certain that the metal has been thoroughly cleaned of blast residue and has not been re-contaminated by oil, containments such as flash rusting, sweat marks, inspection markings and so forth. The inspector may wish to include dew point and relative humidity checks at this points, as well as checks for the metal temperature required for coating or lining application.

• During application, ambient conditions and wet film thickness readings should be monitored. This may not be a required inspection (hold) point for the inspector, but the applicator should be monitoring these conditions.

• An inspection (hold) point following the application of each coat is required to check the dry film thickness against that specified and to determine id each individual coat is suitable to receive the net coat. Such imperfections as over-spray, pinholes, lack of adhesion, insufficient film thickness, etc., should be corrected at this point. Drying/curing time versus temperature and humidity should be confirmed.

• An inspection (hold) point following curing of the completed coating or lining system will verify the final dry film thickness and will include a visual inspection of the coating or lining, a holiday check should be made and any imperfections noted for repair. The degree of cure can be determined either from the retained records of curing temperatures, from hardness tests using the acceptable methods and instruments or even in some cases, by indentation with the thumbnails.

• The final inspection (hold) point will verify any touch-up repair work that was found to be necessary and will be final check for full compliance with the specifications.

What Codes And Standards Should Be Included In the Inspection Plan?

The inspection will usually list the codes or standards that will apply to a particular material and its application. These standards may be ASTM standards or procedures for various test methods, SSPC standards for cleanliness, the SSPC procedures for measuring dry film thickness (SSPC – PA 2), or others. These standards or procedures are listed in the inspection plan for the inspector’s reference.

What Inspection Activities should be Included In the Inspection Plan?

The following inspection plan example covers the application of an epoxy phenolic amine or amine adduct cured coating. This particular coating systen may be used as a protective coating or as a lining. All specifications the inspector might encounter may not require all the points of inspection shown in this particular inspection plan. The information shown can serve as a guide for the inspector in writing an inspection plan for the specification he is working to.

The inspection plan lists a chronological sequence of inspection activities to be accomplished during the coating or lining application. It begins with the activities the inspector should consider prior to the start of the actual coating work and continues through surface preparation and coating application. Each page lists the activity to be performed, the standard or procedure to be followed, where appropriate, the inspection criteria, and a reference to the paragraph in the specification that applies to that activity.

When performing the required inspection activities, each phase of the work is inspected, before proceeding with the next phase. I this way, any defects disclosed by the inspection are corrected to specifications, and re inspected, before proceeding with the next phase. For example, after the surface has been prepared, it is inspected. If any deficiencies are found, they are corrected and the surface is reinspected before proceeding with the application of the first coat. The same procedure is followed for each phase of the work.

The first page of the inspection plan (as in Fig.) deals with the materials to be used for the work. This includes the coating or lining itself, any touch-up or repair materials, thinners and cleaners, and the abrasives to be used to prepare the surface. The inspector must verify that the correct coating or lining materials have been supplied. Material mix-ups are very infrequent on fieldwork; however, in shop application where a shop may warehouse many different coating or lining materials, it is a distinct possibility. The shelf life of a coating or lining material is the length of time it is normally considered to be usable from the time of its manufacture. The inspector must verify that the material is within its shelf life and will remain within in shelf life during the course of application. Often times, the specification will have a shelf life differing from that shown by the manufacturer. The shorter of the two should be used. This is usually a problem on small jobs; but on a job that may extend over long periods of time, the material can run beyond its shelf life prior to completion of the work.

Coating and lining material must be properly labelled. Containers with missing or illegible labels should be set aside and discarded. All coating and lining material should have legible batch numbers printed on the label. These batch numbers are extremely important in identifying a material in the event of trouble. The batch number is usually a several-digit number, occasionally consisting of letters and numbers. The inspector should record all batch numbers in his reports, before the containers are opened and before paint has run down and obliterared the numbers.

Dented containers do not have to be rejected unless the dents are so  sever that the containers have leaked or the contents have been exposed to the atmosphere. If leakage or exposure has occurred, the material must be rejected. Such materials must be segregated and removed from the jobsite.

The storage temperature of most coating and lining material will usually be specified either in the specification or by the manufacturer himself. Usually, a maximum and minimum allowable storage temperature will be indicated. Touch-up or repair material may not always be identical to the coating or lining material being applied.

The material should check the abrasive to be used for surface preparation, if abrasive blasting is specified. The specification will not normally specify a particular abrasive by name, but only the required degree of cleanliness and the profile; however, the supplier’s procedure will often identify a specific product. The abrasive should be clean and dry and of a proper size to produce the required profile. Steel shot or grit must be free of oil, and sand must be free of clay or other contaminants. The grit size on flapper wheels and sanding discs should also be checked where they are specified for use in power tool cleaning that will not be followed by abrasive blasting.

This page (fig.) begins a check on the equipment the applicator or inspector will use, or which should be on hand. The environment control equipment, if required, should be capable of maintaining the specified relative humidity, temperature and dew point. The spray application equipment and brushes or rollers being furnished by the applicator should be as recommended by the manufacturer or as stated in the accepted supplier procedures. One very frequent cause of poor coating of lining application is the use of incorrect or worn out sprat equipment. Also, the use of brushes with the incorrect bristles or the uses of rollers with the wrong nap and core material are frequent causes. The blotter test used to check the air supply for oil containments is mentioned, together with the rquired frequency of testing. 

The inspector should have required inspection equipment available on hand and properly calibrated. (Fig.)

The final items on this page of the inspection plan reference the pre-inspection of the surface prior to the start of abrasive blasting. The inspector may and should assist in the pre-inspection; however, it is the applicator’s responsibility of either accept of reject the surface as being suitable for surface preparation and coating or lining application. Surface preparation (Fig.) includes the removal of grease or oil deposits, in accordance with the requirements of SSPC-SP-1, “Solvent cleaning” prior to the start of abrasive blasting. The blasted surface must conform to the specified deree of cleanliness of the SSPC standards profile. The inspection plan not only indicate what is required but what publications and instruments are to be used to verify of the flotation test used to determine if steel shot or grit is oil-free is stated.

The protection of surface and equipment not to be blasted or coated is listed at the end of the second page (Fig.) covering surface preparation. In actual practice all necessary masking or protection should have been accomplished and inspected prior to the start of any abrasive blasting.

The final step of surface preparation, prior to the application of the coating or lining, is to thoroughly clean of all dust or other contaminants. The inspector must verify that the surface is free, not only of the dust and unacceptable embedments, but of sweat marks and oil contamination from air tools and from the operating mechanism of spiders or sky climbers. He should be alert for imperfections in the base material that have been revealed by the surface preparation.

When the surface has been accepted for the application of coatings or linings, the materials to be applied should be brought from storage to the work area in unopened containers (fig.). The containers should remain closed until just prior to mixing. Under no circumstances should the applicator attempt to measure or mix partial containers. Only complete, pre measured units should be mixed. Some applicators may attempt to proportion a small quantity of coating material for touch-up rather than use a full 5-gallon container, to save on material. Most coating or lining manufacturer will supply materials in 1-gallon, or smaller, containers for this purpose, along with the appropriate amount of catalyst or hardener. Components of a two- or three- component material should be mixed separately and in the proper order, in accordance with the manufacturer’s instructions.

Induction time is the period during which the mixed material is allowed to begin the reaction, prior to being applied.  If induction time is required, this will be noted in the coating or lining manufacturer’s literature. This material aids in coating or lining vertical surface, since after ingestion, a material will tend to hang and not run.

Temperatures of the individual components of a coating or lining and the temperature of the mixed material should be verified during mixing if this is required by the specifications or the procedures.

The specified number of coats, the timing of these coats, time and temperature of any force that may be required, and touch-up are covered in the inspection plan, as shown in above (Fig.)

Wet film thickness readings may be required as the coating or lining work proceeds; however, with most coatings or linings, it is necessary to check the dry film thickness of each coat as soon as it has dried sufficiently. Coatings and linings applied too heavily are susceptible to inadequate curing and to the trapping of solvents, and may later blister or peel. Coatings and linings are also applied in multiple coats to minimise the possibility of pinholes penetrating to the substrate. Whenever possible, multiple coats of contrasting colors to minimise the possibility of the skips or thin areas.

The drying time between coats is of almost importance. If a coating or lining is applied too soon over the previous coat, solvents may trapped in the underlying coating or the underline coat may be lifted or otherwise adversely affected. 

Where force curing of a coating or lining is required, the final curing temperature must be carefully monitored and the temperatures recorded. Remember, the temperature specified is usually the substrate temperature and this can vary greatly from surface to surface, depending upon the configuration of the object being cured and on the method and equipment being used to effect the curing. Tank bottoms setting on concrete slabs or on sand beds, tank saddle supports, and reinforced sections around openings or brackets are all notorious heat sinks. When force curing a lining, the temperature is normally raised in measured increments (for example, a 40 –degree rise in temperature every 30 minutes) until the desired temperature is reached and maintained for the required period of time.

The final page of the inspection plan ( Fig.) covers the determination of the dry film thickness of the applied coating or lining in accordance with the requirements of SSPC-PA 2, in this instance 12 to 18 mils, and states the acceptable thickness or runs or sags.

The inspector is required to make an inspection of the coated surface for coating or lining imperfections, such as overspray, major runs or sags, drips, blistering, pinholes, any loss of adhesion, inadequate cure, etc. any such imperfections must be corrected.

Where the coating application is to be used a lining or in severe chemical services, a holiday test for pinholes or other film discontinuities will normally be required. The method of inspection is covered in specific procedures that are available for using holiday detectors. Any holidays, pinholes or other imperfections revealed by this test must be marked with grease-free chalk or other suitable means and must be repaired and re-inspected.

The inspector should train himself to look for the inaccessible areas that are difficult to blast or coat such as brackets, or behind pipes, inside channels, etc. The coating of structural steel in a fabricator’s yard may be pretty straight forward, but the lining of a tank interior can be much more complicated. Look for imperfections of the large, flat surfaces. Be curious, Don’t accept the premise that, “Since the coating on the wall of a tank looks good, the inaccessible or difficult areas are also good.” Rust running down a tank wall after six months in service will be a testament to an incomplete inspection.