Chemical Compatibility Chart for Pumps: What the Grade and the Temperature Actually Mean

A compatibility chart is only as useful as the reader's understanding of what a letter grade means. This article explains how to read the ratings in our matrix of 37 media against 13 materials, what those ratings are based on, and where we publish the lower number on purpose.

Once you know how the temperature beside each grade is defined, you can screen a duty point yourself — and you will stop being misled by charts that look more certain than they are.

What does the letter grade mean?

A is excellent, B is good, C is conditional, and X means we will not rate the material for that medium.

A C rating always carries a caveat — a velocity limit, a stress-relief requirement, a total-acid-number or sulfur threshold — and the caveat travels with the report. A dagger symbol marks a cell where our sources disagree, and we publish both positions rather than pick one silently.

X is the rating people misread most often. X does not mean the material fails on contact. It means we decline to rate it, because our sources do not support a positive grade, or because the surrounding conditions would decide the outcome and we cannot see those conditions from a duty point.

A plant engineer with the full service description can still reach a different conclusion. Our chart is a screening boundary, not a corrosion prediction.

What does the temperature next to the grade mean?

In our chart, tmax is the temperature at which the rating fails for that specific medium. It is not the material's temperature limit.

This is the single most useful thing to understand about the whole table, and it explains a number that otherwise looks like a mistake. Stainless 316L is rated A at 200°C (392°F) for crude oil and A at 120°C (248°F) for clean water.

Same alloy, same chart, two different numbers. The alloy did not change; the chemistry that defeats it changed.

That distinction is why the temperature travels with the grade instead of sitting in a separate column. Published charts that put a single letter against a material at ambient temperature and then add "derate at higher temperature" are leaving the actual decision to the reader.

In chemical service the interesting band is usually 60–120°C (140–248°F), and that is exactly the band a single ambient-temperature letter is silent about.

Why the temperature band changes with the medium

Because the failure mode changes with temperature, and the mechanisms do not share a curve.

Stress-corrosion cracking is a threshold phenomenon. For sodium hydroxide up to 50%, our matrix rates carbon steel B at 50°C with a stress-relief caveat. Below the threshold the material behaves; above it, residual stress decides the outcome, and that is a fabrication question rather than a materials question.

Oxidising agents behave differently again. For sodium hypochlorite up to 15%, our matrix rates 304, 316L, duplex and Hastelloy C-276 all as X, and puts titanium, PP, PVDF and PTFE ahead. Chloride plus an oxidiser attacks stainless in a way that no amount of grading up the alloy fixes.

Passive films can be a feature. Carbon steel is rated A at 40°C (104°F) for sulfuric acid at 93–98% in our matrix — not because carbon steel resists sulfuric acid, but because the concentrated acid builds and maintains a protective sulfate film. We do not rate the same material for the 50–80% band at all.

Dagger (†) marks a cell where our sources disagree. We do not bold or colour the passing grades, because we do not rank materials.

Three of those rows contradict what most people expect.

Hydrochloric acid is not a stainless-steel application. In our matrix, 304, 316L, duplex 2205 and Monel 400 are all X. The passing answers are the nickel-molybdenum alloy Hastelloy C-276 at 60°C, and the non-metallics — PP at 60°C, PVDF at 80°C, PTFE-lined at 120°C.

Some general references list Monel for hydrochloric acid. Our compilation does not, and we publish the conservative grade rather than split the difference.

Concentrated sulfuric acid is not automatically the harder problem. Dilute sulfuric acid is. Carbon steel gets an A at 40°C for 93–98% acid under four stated conditions, while 304 is X at the same concentration and both 304 and 316L are X below 50%. Concentration is the variable, not the acid's reputation.

Sodium hypochlorite defeats every stainless we carry. If your plant chlorinates cooling water, the wetted material question is not a corrosion allowance question. It is a different material family.

Where the ratings come from, and how much weight they carry

You are owed a straight answer about provenance, because it determines what the chart can be used for.

The matrix is a multi-source compilation built in 2026 by cross-checking pump-maker chemical resistance tables, specialty-alloy producer data and pump material selection guides, taking the conservative grade wherever the sources did not line up.

For most cells, the individual source behind the grade is not recorded on a per-cell basis. That is a limitation we state rather than hide, and it is why the chart is presented as our screening boundary instead of as an industry consensus.

Seven cells carry a named source and are recorded individually.

The remaining cells are compiled and are being re-checked one at a time. When a cell is re-verified against a manufacturer's published data, we update the tool and the date on this page together.

What that means in practice: use the chart to eliminate materials, and to find the media where the answer is not a metal. Do not use it as the final material selection for a purchase order. A pump manufacturer's published data for a specific model outranks a generic matrix, ours included.

What does the chart deliberately leave out?

Three things: hydrofluoric acid and oleum, sulfuric acid in the 80–93% band, and anything above the 150 °C cap on fluoropolymer lining. All three are design decisions, not omissions.

Hydrofluoric acid and oleum are not rated. Both always go to a human.

With hydrofluoric acid the reason is the consequence of a wrong answer as much as the chemistry. HF causes deep-tissue injury and attacks glass and silicates, so the material question extends beyond the pump.

Public content suggests Monel or PTFE-lined construction for HF. We hold a human handover instead. This is not a case we cannot answer; it is a case where the responsibility boundary sits with a specialist, and we say so.

Sulfuric acid between 80% and 93% is deliberately left open. The protective film on carbon steel forms at high concentration and does not survive in the middle band. Rather than interpolate between two buckets that behave differently, we send that band to a human.

PTFE and FEP lining is capped at 150°C (302°F) across the entire table. That cap is ours. Fluoropolymer linings are catalogued to higher figures — at least one European specialist publishes 180°C — and our table stops at 150°C as a screening line rather than as the limit of the material.

What readers assume, and what the ratings actually say

When does this go to a human?

Seven boundaries cause most of them: hydrofluoric acid or oleum, sulfuric acid between 80% and 93%, caustic above the rated concentration band, end-suction duty past 150 m (492 ft) of head or 400 m³/h (about 1,760 gpm), a duty above 151 °C where no cell is rated, and any medium outside the 37 in the library.

The tool returns a report automatically for roughly 31% of duty points. The other 69% end in a handover.

• Hydrofluoric acid, or oleum / fuming sulfuric acid
• Sulfuric acid between 80% and 93%
• Sodium hydroxide above the rated concentration band
• More than 150 m (492 ft) of head on a single-stage end-suction pump
• More than 400 m³/h (about 1,760 gpm) on an end-suction pump
• Above 151°C where no material cell is rated for the medium
• Any medium outside the 37 in the library

A handover is the intended output, not a failure. It carries the duty point to the manufacturer's engineering team with the boundary that triggered it.

Common questions about the chart

Is this an industry standard? No. It is a conservative, multi-source screening matrix built for this tool, with seven individually sourced cells and the rest compiled. Standards bodies publish material specifications; they do not publish a cross-medium pump material chart.

Why does the same alloy get different temperatures in different media? Because the failure mechanism is medium-specific. A caustic solution causes stress-corrosion cracking at a temperature threshold. A hypochlorite solution attacks the passive film. A concentrated acid may build one. One number cannot describe all three.

Can I use the temperature as a design margin? No. Leave the margin to the manufacturer's engineering team. Our number tells you where our rating stops, and picking a duty point just below it is not the same as designing to it.

What if a manufacturer's data sheet contradicts this chart? Follow the manufacturer's data sheet. It is specific to a model, a lining thickness, a seal arrangement and a test method. Ours is generic.

Do you rate gaskets, O-rings and seal faces? No. We select pump type and wetted material. Seal and elastomer selection is specified by the manufacturer's engineering team, and we name that boundary in the report.

What this article does not cover

Note that corrosion allowances, design life, velocity limits and NPSH margins are outside this article. It covers material screening by medium and temperature only. The seven sourced cells are listed above; every other cell in the matrix carries the same provenance limitation, stated once rather than repeated 481 times.

Where the next constraint sits

A material screen is one gate and the pump type is another, and the type is decided first — a duty that cannot be pumped by any of the families here never gets as far as the alloy. Chemical Pump Selection Guide: Risk, Medium and Duty Point — in That Order runs that order and shows how viscosity, solids and shear sensitivity move the family before the material is opened up.

The figure that gets mistaken for a material boundary most often is the 500 cP switch, which is where the recommendation changes rather than where a machine stops working. Centrifugal vs Positive Displacement Pumps: What the 500 cP Line Really Means sets out that gap.

Two adjacent duties are decided by the fluid rather than by the material screen, and both sit one step further along this route: Molten-Salt Pumps: Why Temperature Decides the Machine, Not Pressure (what a melting point does to a machine when the fluid is only liquid because it is kept hot) and Liquid Hydrogen Pumps: What the −253 °C Duty Demands (what a heat leak does when the fluid is close to its boiling point).

Sources