Application guide

FRP Effluent and Process Tanks

The tanks that sit between ordinary water storage and aggressive chemical duty. Why an isophthalic laminate is the usual answer there, and what decides whether it is enough.

The middle band, where general purpose is thin and vinyl ester is overspent.

Most resin questions about tanks get answered at one of two extremes. A domestic or institutional water tank is a general-purpose job, and an acid storage vessel is a vinyl ester job. A large amount of real work in Nepal sits between them: effluent holding and treatment tanks, process water in dyeing and textile plants, plating, rinse and washdown tanks, and cooling tower basins. These are permanently wet, often warm, mildly chemically loaded, and expected to last. That band is where an isophthalic laminate is the usual industry answer, and it is the band this page is about.

What manufacturers build

Fabricators in this category build effluent holding and treatment tanks, process water vessels for textile and dyeing plants, washdown, rinse and plating tanks, cooling tower basins and sumps, and the pipework and launders that connect them. Anything holding food, beverage or drinking water is a separate question, because that turns on an approval for contact with the contents rather than on the resin family. The tanks are often sectional or shop-moulded and assembled on site, which means the laminate specification has to hold across many panels made on different days.

Why this material suits the work

ISO Polyester Resin is an isophthalic unsaturated polyester. The isophthalic backbone is the reason it exists: it is described across the industry as more resistant to hydrolysis, the slow attack water makes on ester linkages over years of contact, than the orthophthalic backbone of a general-purpose grade. For a tank that never dries out, that difference is the whole service life. It is not a strength upgrade and it does not make a laminate chemically inert. Samrat FRP Traders supplies and imports this grade for Nepal; the supplier is Samrat Poly Resins, India. Its supplier Technical Data Sheet, SPR-TDS-IPR, is linked from the product page and positions the grade for laminates facing water immersion, chemical service and sustained outdoor conditions; it does not publish chemical-resistance ratings for particular media.

Required resin characteristics

A backbone chosen for hydrolysis resistance, because the laminate never dries out between uses
Predictable wet-out of chopped strand mat and woven roving, since tank walls are built in several passes that all have to bond
Consistency across panels, because a sectional tank is assembled from parts made on different days
A cure system the fabricator controls, so gel time can be matched to panel size and workshop temperature
Chemical-resistance guidance for the actual contents, obtained from the manufacturer rather than inferred from the resin family

Process context

The lay-up itself is ordinary open-mould work. Reinforcement is placed against a prepared and released mould, catalysed resin is worked through it with roller or brush, and layers are built to the specified wall thickness before the panel cures at room temperature and is trimmed. What changes on this class of tank is the specification work before anyone mixes resin. The contents have to be stated properly: what is in the tank, at what concentration, at what temperature, and whether the duty is continuous or intermittent. Many designs then use a resin-rich inner surface against the contents with the structural laminate behind it. Whether that is appropriate here, and what laminate schedule goes with it, belongs to whoever specifies the vessel and to any standard governing it. Catalyst quantities, cure schedules and laminate schedules are not published on this page.

Advantages

Isophthalic is the chemistry the industry specifies for permanently wet service; this grade sits in that family
Room-temperature cure, so no heated equipment is needed for tank panels
The same familiar hand lay-up process as a general-purpose grade, so nothing has to be relearned
A documented alternative exists in both directions: a general-purpose grade below it and vinyl ester above

Common products

Effluent holding and treatment tanks
Process water vessels for textile and dyeing plants
Washdown, plating and rinse tanks
Cooling tower basins, sumps and launders

Common questions

How do I know whether this is an isophthalic job or a vinyl ester job?

By the contents rather than the category. State the chemical, its concentration and its service temperature, and whether exposure is continuous. Mild, dilute and ambient generally sits in the isophthalic band; hot, concentrated or oxidising duty moves the conversation to vinyl ester. Where the answer is not obvious, the manufacturer’s chemical-resistance guidance for the specific grade decides it, not a general article.

Could I just use a general-purpose resin and make the wall thicker?

Thickness does not address hydrolysis. A general-purpose laminate in permanently wet service is exposed to the same slow attack throughout its thickness, and a thicker wall mainly buys stiffness. This is the reason the isophthalic grade exists as a separate product rather than as a premium version of the same one.

Is this suitable for drinking water?

That is a separate question with a separate answer. Potable-water suitability depends on an approval covering contact with drinking water, and it has to name the whole construction including any gelcoat or lining on the wetted face. It does not follow from the acid used in the resin backbone. Ask which standard or certificate is required and we will put that to the supplier.

Where are the technical figures for this grade?

On the ISO Polyester Resin product page, taken from the supplier Technical Data Sheet (SPR-TDS-IPR, Rev. 01, September 2026) with the issuer named. This guide does not repeat them, and the sheet does not publish chemical-resistance data for specific media: for a particular chemical, concentration and temperature, ask us and we will put the question to Samrat Poly Resins, India.

What else do I need besides the resin?

Reinforcement and a catalyst system at minimum: glass fibre mat for the laminate and an MEKP hardener, with a cobalt accelerator where the system calls for one. Whether the wetted face also needs a gelcoat is a design decision for the vessel.

Specifying an effluent or process tank?

Tell us the vessel, what it holds, the concentration and temperature, whether exposure is continuous, and any standard your project names. We will review the grade and the current supplier documentation with you.

Contact Samrat FRP Traders