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Article # 0033

Equipment and Processes Used at  “Cured in Place Pipe” (CIPP) Wetout Facilities

by

Karen M. Bullard, P.E.

 

 

INTRODUCTION

 

This paper will describe the equipment and processes used at a “cured in place pipe” (CIPP) wetout facility.  This type of facility manufactures liners for the rehabilitation of underground sewer lines and similar piping.  The liner functions as a type of “patch” or replacement piping. The liner is essentially a polyester felt bag filled with liquid un-reacted vinyl ester or polyester resin.  The liner is transported by refrigerated trucks to the customer’s site where steam or hot water is used to initiate the polymerization reaction.  The end product is a tough, secure, patch or replacement pipe of the exact dimensions required by the customer. 

 

EQUIPMENT DESCRIPTION

 

The process equipment at a CIPP wet-out facility generally consists of the following:

 

 

Refrigerated Bulk Storage Tank

 

Resin is provided from bulk storage tanks, totes and/or drums that are kept in refrigerated storage.  In bulk storage, the polyester resin is stored in small (approximately 6000 gallon capacity) fixed-roof refrigerated and insulated storage tanks maintained at approximately 68oF. 

 

Catalyst Mixer

 

A five gallon capacity mixer is generally used to mix powdered and liquid catalyst with styrene.  This type of mixer uses a dispersion blade and is covered during operation.

 

 

 

 

Static Mixing System

 

The static mixing system mixes a metered, constant amount of the styrene/catalyst mixture from the catalyst tank into the bulk resin prior to liner impregnation.  The catalyst tank has a capacity of 15 gallons.  The control system for the static mixer monitors catalyst flow, resin flow, catalyst pressure, position of catalyst valve & resin valves, and resin pressure.  The entire system is enclosed.

 

 

Double Drum Mixer

 

An alternative mixing system that may be used is the double drum mixer.  An air-powered double drum mixer generally has the ability to mix two 55 gallons drums of resin at the same time.  Air-powered rams are used to lift the mixer out of the drums.  These mixers are covered during the mixing process.

 

Vacuum Pump System

 

The liner material is essentially a felt bag with an impermeable outer coating.  A small vacuum pump is generally used to remove any air inside the liner.  A typically-used pump is a single-stage, oil-sealed rotary vane pump.  The vacuum is maintained during the filling of the liner.  Since the liner has been evacuated prior to impregnation and the system is closed, there is a minimal amount of exhaust from the vacuum pump.

 

PROCESS DESCRIPTION

 

A CIPP wetout facility manufactures liners for the rehabilitation of underground sewer lines and similar piping.  The liner functions as a type of “patch” or replacement piping. The liner is essentially a polyester felt bag filled with liquid un-reacted vinyl ester or polyester resin.  The liner is transported by refrigerated trucks to the customer’s site where steam or hot water is used to initiate the polymerization reaction.  The end product is a tough, secure, patch or replacement pipe of the exact dimensions required by the customer. 

 

Since polymerization of the resin does not occur at the manufacturing facility, the only emissions at the manufacturing facility from the production of the patches occur as a result of the mixing and liner impregnation operations. 

 

Preparation of Styrene/Catalyst Mixture

 

The first step in the manufacturing process is the preparation of a catalyst/styrene mixture.  Although the amounts and types of catalyst may vary slightly, in general, a powdered catalyst, a liquid catalyst, and liquid styrene are mixed together.  The powder is added to the liquid styrene to prevent dust emissions and the chemicals are mixed in a covered 5 gallon mixer.  The catalyst is mixed with the styrene to facilitate the addition of the proper amount of catalyst to the resin mixture.  The styrene in the catalyst/styrene mixture reacts with the resin mixture in the final product at the customer site to become part of the polymer matrix.  The styrene is therefore not a solvent, but a reactant in the final product.  Generally, up to 3 batches of the catalyst/styrene mixture (15 gallons total) may be mixed in one hour to fill the hopper of the static mixer.

 

The catalyst/styrene mixture is added to the hopper of the static mixer and the closed-loop mixing begins as the resin is pumped from the bulk tank or totes.  If it is the beginning of a production day, or if a batch of a different composition is beginning, a small amount of the catalyzed resin may be purged from the system to assure product quality.  In general, the maximum amount of waste generated in this manner is two gallons/day.  This waste is placed into a 55 gallon drum fitted with a spring-loaded pressure relief valve in the bung hole.  A small sample (20-30cc) may also pulled from the drain tube of the mixer at the beginning of the batch to test the gel time of the mixture.  

 

Resin Impregnation of the Liner

 

The liner impregnation process begins as the resin is pumped from the storage tank through the mixing tube where the static mixer continuously adds the catalyst/styrene mixture in the appropriate amount.  The catalyzed resin mixture is pumped into long felt bags, which are kept under vacuum to prevent air from entering the patch material and to facilitate the even impregnation of resin into the felt.  The felt itself is coated with an impermeable polyurethane coating.  As a result, most of the emissions that occur from the mixing and filling processes are exhausted through the vacuum system. 

 

The liners are impregnated with resin on a conveyor bed.  The nozzle for the static mixer hose is placed into a small slit which is cut through the outer polyurethane coating of the liner.  This nozzle may be sealed to the liner with duct tape and then the initial “slug” of resin is added to the liner.  The liner is then rolled forward on the conveyor, passing through the pinch rollers which push the resin down the liner, leaving the appropriate amount of resin in the product for the diameter and application of the liner.  In general, the impregnated liner will be loaded continuously into a refrigerated truck.  If the length of liner requires more resin than what is dispensed with the initial slug, a new slit is cut in the liner at the appropriate location and another slug is added. 

                                                                                   

Repair of Slits in the Liner

 

The vacuum system draws a vacuum through a slit made at the end of the liner to which a vacuum cup is attached.  When a liner is fully impregnated with resin, the vacuum hose is removed from the slit and a patch is applied to the resulting hole in the felt liner.  To repair the hole, THF is generally used as an adhesive-like material.  A small amount of THF is painted on the hole and a polyurethane patch is applied.  The THF solvent causes the polyurethane coating on the bag and the patch material to become soft enough to bond together in a secure patch.  The same process may be used to repair the slits at the top of the liner that are cut where the nozzle adds the resin. 

 

Double-Drum Backup Mixing System

 

As a backup system or for smaller jobs, a double-drum mixer may be used to mix resin and catalyst.  In this process, the lids are removed and the mixer impellers lowered into the drums of resin.  The drums are then covered and the resin is mixed.  Then, the catalyst is added, the drums are covered, and the catalyst is mixed into the resin.  After the resin is mixed, an air-powered diaphragm pump is used to pump the resin into the liner.  The rest of the process remains the same as described above for the static mixing and liner impregnation process.

 

Cleaning

 

At the end of a production run, the injection nozzle and any other equipment that may have been in contact with the resin material is wiped down with a small amount of acetone.  The static mixer may be equipped with a pressure canister that allows cleaning of the injection nozzle with about one gallon of acetone under air pressure.  The nozzle may be inserted into an enclosed 55 gallon drum to collect the acetone/resin mixture as it is discharged from the nozzle.  A small amount of acetone may also be used to clean the catalyst mixing and the double-drum mixing equipment.

 

Biography 

Karen M. Bullard, P.E. is an Engineering Partner and the President of Bullard Environmental Consulting, Inc.   She has over 13 years experience in environmental engineering, compliance, and permitting.  She worked for the Texas Commission on Environmental Quality (TCEQ) for four years as an Air Permit Specialist in the Coatings and Combustion Section, where she developed a thorough understanding of the governmental procedures and policies in Texas.    Karen has a Bachelors of Science Degree in Chemical Engineering from the University of Texas at Austin.

Karen M. Bullard, P.E. No. 88449

Final Edition Completed June 28, 2007 from Previously Composed Material

 

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