Winterising an IBC in Central Texas

What actually happens in a hard freeze

A full 275 gallon container holds about 2,300 lb of water. Water has an enormous specific heat capacity and an enormous latent heat of fusion, which is a technical way of saying that a full container is a large thermal battery. In a two-day event at 20 °F with no wind, the bulk of that water does not freeze. A skin forms, the top few inches go slushy, and the core stays liquid.

The parts that do freeze are the ones with a large surface area relative to their volume: the valve body, the outlet neck, any pipework, and anything sitting in a pump housing. Those freeze within hours, not days. And unlike the bottle, they are rigid — a brass or stainless valve body does not expand to accommodate ice, it cracks.

What February 2021 actually broke

We were asked to assess a lot of damaged equipment in the weeks afterwards, and the pattern was remarkably consistent across sites. Out of roughly 200 containers we looked at:

Read the last three rows. Three percent of bottles failed in the sidewall, and nearly all of those had a fold in them already. The container is not the weak point in a Texas freeze; the fittings are. That is good news, because fittings are cheap and preventable.

The checklist

Two days out

• Decide, per container, whether it is in service or out of service through the event. There is no useful middle state.
• Out of service: drain completely through the valve, leave the valve open, leave the lid loose. An empty container with an open valve cannot be damaged by ice.
• In service: top it up. Thermal mass is the whole defence.
• Disconnect and drain every hose. Coil them indoors.
• Drain and store pumps. A primed pump left outdoors is the most expensive item on this list.

The day before

• Insulate the valve. A jacket, a wrap, even a bucket of straw taped over it — the valve is the part that breaks.
• Heat-trace any run of pipe you cannot drain, and confirm the circuit actually works before you need it.
• Leave headspace. A brim-full container has nowhere for a surface skin to expand into, which is exactly how the eleven percent of top-radius failures happened.
• Move anything you can into a building. A container in a warehouse is a non-problem.

During

• Do not run a pump against a frozen line. That is how you turn a $40 problem into a $600 one.
• Do not apply direct flame or a heat gun to HDPE. It softens near 175 °F and it will deform long before the ice moves.
• If you must thaw a valve, use warm — not hot — water poured over a wrapped valve body, patiently.

Design choices that make this easier

If you are specifying a new installation in this climate, four decisions make freeze season almost boring.

1. Put the draw point at the bottom and slope every run back to it. A system that drains by gravity in ninety seconds gets winterised properly, because nobody has to be conscientious about it.
2. Use a jacketed or insulated valve enclosure from the start. It costs a few dollars and it removes the single most common failure.
3. Specify unions either side of anything you might need to remove. Pumps come off in two minutes or they do not come off at all.
4. Site the array against a south-facing wall if you can. In Central Texas, a wall with a day of sun on it is worth several degrees overnight.

Our own array survived 2021 because somebody walked out on the Saturday and opened eight valves. That is the entire technology.