A data‑driven guide to picking inhibitors, biocides, and materials that can coexist for years inside cement plant closed loops — without sacrificing reliability or compliance.
Industry: Cement | Process: Closed
Closed‑loop cooling systems recycle the same water, so treatment centers on corrosion, scale, and biofouling control — without the continual water losses typical of open towers. Common corrosion inhibitor families include nitrite, molybdate, phosphates (orthophosphate and polyphosphates), silicates, and organic amines/film‑formers. Nitrite is widely used (effective at moderate chloride, inert to dissolved oxygen) but is biodegradable and can promote microbial growth, which drives frequent biocide “pulses” or bleed‑off (content.ampp.org) (content.ampp.org).
Molybdate works well at low chloride but is costly and faces discharge limits in some regions (content.ampp.org). Phosphate and polyphosphates — and phosphonates like ATMP (aminotris(methylenephosphonic acid), a common organophosphonate) — are broad‑spectrum inhibitors that also help buffer pH; compatibility charts rate these “A” (excellent) with common seal materials (walchem.com). Historically, borate was added as a pH buffer (pKa ~9, the acid dissociation constant) but new health/environment concerns — the EU classifies borates as toxic to reproduction — are driving phase‑out (content.ampp.org). New inhibitor chemistries (phosphate‑free organic blends) are emerging to meet stricter safety and discharge rules.
In practice, these chemistries are delivered as part of corrosion and scale programs, including options such as corrosion inhibitors, dedicated scale inhibitor feeds, and integrated closed‑loop chemicals.
Biocide strategy and dose control
Closed loops typically use non‑oxidizing biocides such as glutaraldehyde, isothiazolinones (e.g., CMIT/MIT blends), quaternary ammonium compounds (QACs, a cationic disinfectant class), and specialty phosphonium biocides, along with occasional oxidizers like chlorine dioxide (ClO₂) or hydrogen peroxide (patents.google.com) (patents.google.com). One industry survey cited glutaraldehyde, isothiazolone and tributyltetradecyl‑phosphonium chloride as top non‑oxidizers, and ClO₂ and H₂O₂ as leading oxidizers (patents.google.com) (patents.google.com).
Non‑oxidizers generally require longer contact time but present no direct corrosion risk; oxidizers like chlorine dioxide kill rapidly but attack many materials. Operators often alternate biocides to prevent resistance and keep total biocide usage moderate. Industry trends point to more biodegradable and less toxic biocides, automated dosing, and real‑time monitoring (e.g., online microbial sensors). In closed‑loop programs, these “measure‑and‑respond” regimes are commonly enabled by metered addition using equipment such as a dosing pump and standard controls sourced from water‑treatment ancillaries. Biocide packages are widely cataloged under biocides.
Metals and corrosion control envelope
Common metallurgy is carbon steel (CS) cast iron/steel, 300‑series stainless steel (SS), copper/brass, and increasingly aluminum alloys, with galvanic couples considered carefully (for example, avoiding copper paired with CS or compensating with aggressive treatment). Inhibitor selection depends on metallurgy: nitrites and molybdates protect CS well, while copper surfaces need azoles (e.g., benzotriazole) or high pH ammonia. Typical closed loops run 35–80 °C and use nitrite/molybdate or proprietary organics for CS protection (content.ampp.org).
Nitrite does not require dissolved oxygen to function (content.ampp.org), which suits de‑aerated loops, but biogrowth can draw it down and force costly water replacement (content.ampp.org).
Elastomers in contact with treatments
Key elastomers include EPDM (ethylene–propylene rubber), Buna‑N/NBR (nitrile rubber), Viton™/FKM (fluoroelastomer), Neoprene™/CR (chloroprene rubber), silicone (VMQ), and specialty FFKM (perfluoroelastomer). Material charts and vendor tables generally rate these as excellent for inorganic inhibitors. For example, a Walchem chemical‑compatibility guide shows sodium nitrate, sodium phosphate, and sodium silicate rated “A” with EPDM and FKM (and PVC/PP) (walchem.com) (walchem.com). The same chart flags only a caution for stressed 316SS surfaces, which it rates “B” for nitrate (walchem.com).
Compatibility with biocides is more challenging. Oxidizers (chlorine, chlorine dioxide, peroxide) attack many rubbers. Only Viton (FKM) and PTFE are reliably “suitable” for seals in chlorine dioxide environments; Buna‑N/NBR and many other elastomers are not recommended (efunda.com) (efunda.com). In practice, chlorine‑based oxidizers or high oxidizer levels lead to specifications with FKM (Viton) or even PTFE for O‑rings and gaskets. EPDM is generally good with non‑oxidizing biocides (isothiazolones, glutaraldehyde) and strong alkaline buffers, but it can degrade with strong organic solvents or high aromatics. Silicone rubber has poor chemical resistance overall (especially to acids and many organics) and is rarely used in industrial loops. Nitrile/Buna‑N tolerates oils and some acids, but compatibility charts often rate it poorly on chlorinated solvents and ketones (efunda.com) (efunda.com), so exposure to halogenated biocides or high‑temperature glycols is avoided.
Plastics and fluoropolymer choices
Most plastic pipe and valve internals in these services are polypropylene (PP), polyvinyl chloride (PVC/CPVC), PVDF (Kynar®, also listed as PVF2), or PTFE (polytetrafluoroethylene). These are inert to almost all closed‑loop chemistries: Walchem’s data show PVC and PP rated “A” for phosphates, silicates, nitrates, sulfites, and related treatment ions (walchem.com) (walchem.com). PVDF and PTFE have even broader resistance (PVDF’s typical maximum service temperature is about 150 °C; beyond the needs of most closed loops). Nylon and other polyamides are not used in hot loops due to water absorption and hydrolysis. For aggressive treatments (especially oxidizers or acids), fluoropolymers (PVDF, PTFE) or Teflon‑lined components are preferred. Where practical, EPDM/FKM seals and PVC/PP/PVDF plumbing are selected for chemical resilience.
In harsher oxidizing conditions or where housings and accessory components must resist chemical attack, some users favor polymer or composite hardware, a choice that aligns with the use cases served by specialized housings such as a PVC‑FRP cartridge housing.
Material compatibility highlights
EPDM (EPR): Excellent with water, chlorides, silicates, phosphates, and strong alkalis (nitrite, molybdate, etc.); good with oxygenated organics. Not suitable for oils, hydrocarbons, ketones. Sensitive to ozone.
FKM (Viton): Excellent broad chemical resistance, including chlorine dioxide and organic solvents (except very strong ketones). The best choice for oxidizers and hot water loops (efunda.com).
Nitrile (Buna‑N): Good for hydrocarbons and neutral water; rated poorly on oxidizers (e.g., ClO₂, [70†L13‑L19]), ketones, and strong acids. Suitable if no aggressive organics or halogens are present.
Neoprene (CR): Similar to nitrile; moderate acid and chlorine resistance, but generally less robust than EPDM or Viton.
Silicone (VMQ): Very poor resistance to most chemicals (except very weak solvents); avoided in cooling loops.
Plastic (PVC/CPVC, PP): Good for most inhibitors (nitrates, phosphates, silicates, bisulfite) (walchem.com). PVC/CPVC not recommended for strong oxidizers or high temperature (>60 °C typically).
Plastic (PVDF, PTFE, PFA): Highly inert. Rated “A” with virtually all closed‑loop chemistries (walchem.com). Used for unusually corrosive conditions.
Example: Compatibility guides rate sodium silicate (common in carbon steel protection) as “A” for EPDM and FKM, and sodium nitrate likewise “A” on EPDM/FKM (walchem.com) (walchem.com). In contrast, chlorine dioxide is only “suitable” on Viton or PTFE (efunda.com), while nitrile would fail rapidly (efunda.com). These data‑backed charts are consulted when matching a candidate inhibitor/biocide against each gasket or plastic.
Design checklist for long‑term compatibility
1) An effective program inventories all wetted materials. The list spans metals, elastomers, and plastics (pipes, exchangers, pumps, sealants, O‑rings, coatings). For each, chemical‑resistance charts are checked to ensure proposed chemicals rate “Good/Excellent” (A/B) for each material (walchem.com) (walchem.com), avoiding known bad combinations (for example, nitrile exposed to chlorine‑bearing biocides, which are listed as not recommended: efunda.com) (efunda.com).
2) The inhibitor program matches the metallurgy. Where carbon steel and copper coexist, both ferrous and non‑ferrous protection are included (for example, nitrite/amine plus an azole). Chemistry that would poison the installed metals is avoided (for example, fluoride or chloride oxidizers vs. bronze). pH buffers (amine or phosphate) maintain the metals’ safe zone. Certain inhibitors (nitrite) require residual monitoring because they are depleted over time (content.ampp.org).
3) Elastomer seals follow the chemistry. Loops treated with oxidizing biocides or high‑pH amines are typically paired with FKM/Viton or EPDM seals rather than Buna‑N. Chart data show only Viton/PTFE are chlorine‑dioxide compatible (efunda.com). With glutaraldehyde or THPS (tetrakis(hydroxymethyl)phosphonium sulfate, a phosphonium biocide), EPDM is usually acceptable, with verification via soak tests on sample O‑rings if needed.
4) Pipe and valve materials reflect the risk. Plastic‑lined or polymer piping (PVC, PP, PVDF) is used for corrosive chemistries; even CPVC can handle common inhibitors. For metallic piping, 316SS is protected by molybdate/silicate if chlorides approach 50 ppm. Where aluminum is present, chlorides are managed carefully, with sacrificial anodes or dual‑metal inhibitors considered.
5) Chemistry is monitored and controlled. Regular testing tracks inhibitor levels (for example, nitrite at ≥200 ppm) and biocide residuals. Excess acidity or oxygen ingress accelerates attack even on “compatible” materials. Oxygen is mitigated with degassing or scavengers (e.g., hydrazine or sulfite) if the loop is tight and oxygen intrusion is possible (content.ampp.org) (content.ampp.org).
6) Regulatory compliance is checked. Indonesian and local environmental limits (e.g., KLH/BLH rules) on discharge metals or toxic biocides apply; while closed loops ideally avoid discharge, blowdown or purification may produce waste. Prohibited chemicals (for example, heavy‑metal chromates) are avoided, and SH&E concerns around borate are considered (content.ampp.org).
7) Mechanical design reduces risk. Dead legs and crevices, where biocides may stagnate, are minimized. All components (valves, sensors) are rated for the maximum chemical concentrations. For pumps, elastomer diaphragms are specified as compatible with the chosen program per manufacturers’ chemical guides.
8) Documentation and testing are formalized. Before commissioning, compatibility is verified by immersing representative seals and pipe samples in the proposed full‑strength treatment solution for an extended period. Manufacturer datasheets and MSDS’s are included in the design review. Material lists are updated whenever the chemical program changes.
9) Ongoing inspection is routine. Periodic leak/failure checks of seals and corrosion monitoring (coupon or probe) are scheduled. Even “A‑rated” materials can swell (changing compression set) or erode at elevated temperature. Trends in pressure drops and leak rates are tracked as early warnings of incompatibility.
Example checklist entry: “Inhibitor: sodium nitrite (200 ppm). Check tubing seals: EPDM (OK), Buna‑N (marginal – avoid). Biocide: DMDA/FAD (Quat). Materials: EPDM proofed by charts, no nitrile present – OK. CIP: flush and re‑test O‑rings after 1 month.”
Source‑backed selections and system reliability
Across inhibitors and biocides, the recurring theme is materials matching. Walchem’s compatibility data underpin selections for nitrates, silicates, phosphates, and sulfites (walchem.com) (walchem.com), while elastomer choices in oxidizing regimes follow efunda’s guidance on chlorine dioxide (efunda.com) (efunda.com). Industry analyses frame the corrosion control envelope and operational realities — including 35–80 °C operating ranges, nitrite’s oxygen independence, and biocide dosing trade‑offs — with detailed context from AMPP and application reports (content.ampp.org) (esmagazine.com) and technology surveys (patents.google.com) (patents.google.com).
