Wrapping Tape Coating

Wrapping Tape Coating

We are highly engrossed in providing Wrapping Coating Services in all Over India. These services are widely performed on pipes, to protect them from corrosion, abrasion, chemicals and other elements. Our offered Wrapping Coating Services are highly acknowledged for their timely execution, excellence, reliability, and high-quality. We are well-equipped with the latest tools and techniques, which are required for rendering a high-quality service

wrapping system shall comprise the followings sequences:

(A) Surface Preparations:-

Prior to brush cleaning, all oil, grease on the pipe surface shall be thoroughly removed by flushing with suitable solvent and wiping with clean tags.

Rusted materials surface shall be adequate scrubbed manually with stiff wire brush where ever surface get rusted, prior to application of primer.

Surface shall be completely free from rust, mill scale, grease, weld spatter, weld slag, dirt, dust, oil and any other foreign matter and to be dry at time of application.

Oil and grease shall be removed using an approved solvent. White spirit and paint thinners are suitable solvents. Kerosene shall not be used.

Mechanical cleaning machines shall not employ knives or other tools, which may produce notches or gauges on the pipe surface.

Blast cleaning machines shall be maintained in correct adjustment and replacement tools shall be available throughout the cleaning process.

All weld joints shall be cleaned manually with stiff wire brush/buffing

The coat of primer shall be given as soon as practicable and before detrimental corrosion or recontamination occurs. The cleaned surface shall never be left unprotected overnight.

The cleaning method employed shall not result in thinning of the pipe wall beyond the limits of the pipe specification.

Cleaning shall be carried out immediately before application of the priming coat and shall be to the satisfaction of OWNER. If the outside of the pipe becomes contaminated with any foreign matter.

(B) Application of Primer:-

Immediately after cleaning the surface shall be applied with one coat of primer before application of coal tar or bitumen tape wrapping. The entire surface of pipe should be primed.

The primer shall be applied in a thin layer without runs, sags, drips, holidays (gaps or voids) or other defects.

If any defects may be found in the primed surface, the pipe shall be re-cleaned and primed to the required standard and to the satisfaction of principal/engineer.

No specific time gap between two coats needs to be maintained but after the coat of primer, the coating should before the primer is completely hardened.

The primer shall be suitable for brush or spray application and still form at thin uniform coating with an approximate 40 micrometer dry film thickness according to vendor’s instruction.

Freshly primed pipe shall be properly supported on racks, and allowed to be uncontaminated by moisture, dirt or other foreign matter.

If application is done in cold weather, the surface of the pipe shall be pre- heated until it is warm to touch and traces of moisture are removed and then primer shall be applied and allowed to dry.

Coating and wrapping shall not be started until that section of line has been tested and accepted.

The primer shall be suitable for brush or spray application and still form at thin uniform coating with an approximate 40 micrometer dry film thickness according to vendor’s instruction.

Primer shall be applied at an average rate 0.12 liter per square meter.

(C) Application of Coating (Wrapping):-

The pipe shall be kept on a suitable platform with ease of rolling so that the enamel can be applied manually with brush/spray so that it will spread uniformly on the metal surface.

Immediately, wrap of coal tar as per approved specification shall be applied over the coal tar enamel.

The total, clean, dry prepared surface shall be spirally wrapped with the laminated tape with min 15 MM or as per Specification overlapped using sufficient tension to ensure complete conformability. Any bulges formed at covers may be removed by splicing the tape in site and repress ring.

The inside of the coal tar is heated with burner and is pressed against the metal with hands so that there is no air gap and with required overlap (i.e. 15mm).The coating shall be continuous for the full length of the pipe except 200 mm at both ends of the pipes.

The tape shall be applied with tension controlled provide a uniform, tightly adhesive coating free from wrinkles, puckers, void, or break.

When the wrapping shall be performed “AT SHOP” or “AT SITE” (when it is necessary to stock the wrapped pipes), an outer wrap shall be spirally wound over a clean dry Primer with 15 mm minimum overlap using sufficient tension to ensure complete conformity. No bulges shall be permitted.

End laps between adjoining rolls of the wrap or between pipe sections shall be a minimum of 150 cm

There after the pipes are lifted by suitable methods and allowed to dry on wooden sleeper/Sand bags. It is done at 2meter distance from digging area.

(D) Handling of Coated Pipe:-

All coated pipes shall be handled in such a way that the coating does not suffer damage.

Coated pipe shall be handled at all times with wide non-abrading slings or belts, or other equipment designed to prevent damage to the coating. All skids used to support coated pipe shall be padded.

Bar cables, chains, hooks etc. shall not permitted to come in contact with coatings. Coated pipes shall be supported at two bare ends cleared from ground either on kids or sand bags.

If the pipeline protective coating suffers damage between the coating and laying operations, the Contractor shall replace or repair the coating to the satisfaction of the OWNER

Pipe shall normally be lowered into the trench immediately after the coating and wrapping has been approved. Where coated and wrapped pipe is supported on padded skids, their number shall be sufficient to ensure that no damage will be caused to the coating and wrapping.

All coated and wrapped pipes which have been supported in any manner on padded skids, or lowering devices, shall be subjected to closed inspection to see that the coating is undamaged before the pipe reaches the bottom of the trench.

Backfilling shall be carried out immediately after the pipeline is lowered into the trench but Contractor shall first obtain the approval by OWNER. If any backfilling is carried out without this approval, OWNER will have the right to require the Contractor to remove the backfill for examination of the coating and wrapping.

(E) Inspection of Wrapping Pipe:-

After application of tape coating, visual inspection shall be carried out for uniformity without any wrinkle, irregularities and over lapping width.

Visual inspection shall ensure that the coating is continuous, that the overlap is correctly maintained and that there are no wrinkles in the tape.

All coating shall be subjected to 100% visual inspection and 100% inspection with an electrical holiday detector before being lowered into the trench.

Thickness of the coal tar enamel coating shall be measured with the digital thickness gauge. Minimal acceptable thickness shall be 4mm or as per Specifications.

Testing of Wrapping by Holiday Test :-

The holiday detector shall be used to check that there is a continuous coating over the pipe surface, particular attention being given to bends and to areas where the tape has been spliced or repaired.

Holiday detection shall be carried out only in dry weather conditions.

Inspection for holidays are carried out on all buried field and shop components prior to back filling. All field joint coated areas to be tested & free from contaminants such as sand, grease and moisture. It shall be performed on completely finished coatings.

Prior to back filling, all wrapped pipe shall be holiday tested using an approved holiday tester set at 5KV per mm of tape thickness to a maximum of 15KV.

The holiday detector shall be of an approved type and the operating voltage and setting shall be determined by a method approved by OWNER.

The holiday detector settings shall be checked at least twice per day, while it is in use.

The calibration report for the Holiday detector will be submitted for review before carrying out Holiday detector testing

Testing Voltage:-

The applied output voltage of the holiday detector shall have a spark discharge of thickness equal to at least twice the thickness of the coating to assure adequate inspection voltage and compensate for any variation in coating thickness. The electrode shall be passed over the coated surface at approximately half the spark discharge distance from the coated surface only one time at the rate of approximately 10 to 20 nd min.

The edge effects shall be ignored. Excessive voltage shall be avoided as it tends to induce holidays in the coated surface thereby giving erroneous readings.

Test Voltage (IS 15337)
Thickness of Coating Test Voltage, Max
2 mm 5KV
3 mm 8-10KV
4 mm 10-12KV

The electrical equipment used to test tape wrapping shall be a portable, low amperage, adjustable voltage, pulse type holiday detector. It shall be furnished with a coil spring electrode or, a suitable brush type electrode. The primary input wattage shall not be higher than 20 W and the minimum pulse at crest voltage shall be 20 per second.

The wrapping machine shall be equipped with an overlap control device properly adjusted to provide the following minimum overlap under all conditions.

Testing Voltage:-

The Visual inspection of the wrapped and coated is carried out to see that the overlap is correctly maintained and there are no wrinkles, voids, blisters, pinholes, open seams, entrapped air or any other defects likely to cause failure of the coating.

The electrode of the holiday detector, which is in the form of a coil spring, is put on the surface of the coated pipe

The voltage of the holiday detector is set by the operator using the adjustable knob.

At no point of time the voltage will be allowed to go beyond 15000V. To ensure proper inspection voltage the equipment shall be grounded properly and the voltage adjusted in accordance with the instructions of the equipment manufacturer.

After the voltage adjustment the electrode shall be passed over the taped surface one time only at the rate of approximate 15 m /min. If the electrode shall be passed over the coated surface, the current to the electrode should be immediately cut off to avoid damaging the coating.

The location of the holiday should be marked using chalk/crayon. That 3” on either side of defective portion of the tape is to be cut opened and removed and fresh tape of that size or slightly larger than that is to be applied using the same application procedure.

The report for the above test will be documented as per approved format.

Precaution:-

It is not intended that the holiday detector should be used to reveal pin holes and minor faults in the inner tape wrap. Such defects would not normally show up on the holiday detector with the specified coating system, unless the voltage was set at a level, so high, that it would be likely to damage the coating.

At no time, shall the holiday detector be permitted to remain stationary around a coated pipeline with the operating voltage switched on.

All defects, whether discovered visually or by means of the holiday detector, shall be clearly and indelibly marked.

To ensure continuity between the brushes or rings, a short circuit test shall be carried out at regular intervals to determine the efficiency. If brushes are used, these must be cleaned every day.

Repair of Wrapping Coating:-

All defects in the coating shall be made good immediately after their detection.

In the time of holiday test if any defective work is found, remove the wrapping and coating to the required extend from those areas by using a sharp knife. Then heated enamel shall be applied manually over the area following the procedure described above and inner and outer wrap applied.

The Contractor shall be responsible for the complete cost, including cost of materials, of making good all defects caused by incorrect storage, handling, application, erection and testing of the protective coating or caused by incorrect construction of the pipeline.

In the event of numerous defects in the coating, OWNER shall have the right to order the whole coating to be stripped, the pipe cleaned and another coating provided, applied and tested in accordance with this specification at the Contractor’s expense.

Holiday or localized defects in the inner tape wrap shall be repaired by the following procedure:

(a) Strip off outer wrap from affected area, after ensuring that completed coating on either side is properly secured to prevent the outer wrap from unraveling.
(b) Strip off inner wrap and primer from the affected area and thoroughly clean the pipe surface.
(c) Re prime in accordance with this specification.
(d) Apply patch of inner wrap not smaller than 150 mm x 150 mm (6″ x 6″).
(e) Test for continuity of repaired inner wrap with holiday detector before replacing outer wrap.
(f) Replace outer wrap and secure firmly.