What jacketing should go on an outdoor chemical storage tank in Texas sun and rain?
Use stainless steel, not aluminum, with corrugated sheet on the shell and gored stainless on the heads, at the gauge and finish the plant specification calls for, held with stainless bands and wire and sealed at every opening. Put a rigid insulation such as phenolic under the top head so people can walk on it without crushing it, and lap every seam so water runs off instead of in.
Chemical storage tanks often sit outside on a pad, where the insulation and jacket take Central Texas sun, rain and the occasional hard freeze. When a chemical spill gets into the insulation, the whole system has to come off and go back on.
That is the job we priced this fall: one acid storage tank at an industrial plant in Central Texas, a mid-size vertical tank with dished heads top and bottom. We insulated two similar tanks at the same plant in 2020. This post is what both jobs taught us, written for plant engineers, maintenance managers and the contractors who work for them.
Why stainless, and why corrugated
Aluminum jacketing is the default on a lot of outdoor piping. It is the wrong choice on a chemical tank. Acids and caustics attack aluminum, and a splash or a drip from a fill line will eat through it. Stainless steel holds up far better, and most plant specifications for chemical areas call for it. If the chemical is aggressive, ask the owner's engineer whether 304 or 316 stainless fits the service.
On this shell we use corrugated stainless to match the sister tanks beside it. The 2020 tanks got smooth stainless. Corrugated has real advantages on a tall shell:
- It is stiffer. The ribs resist dents and oil-canning when a ladder or tool leans on it.
- It hides small dents. A smooth sheet shows every mark in full sun.
- It goes on fast. Sheets wrap the shell in rings and flex around the curve.
Gauge matters. The plant specification on this job calls for .020 inch stainless on the shell and .032 inch smooth stainless on the heads. Suppliers stock different gauges and finishes, and the tanks you are matching may have been built to an older specification. Check gauge and finish line by line on every jacket quote, against both the specification and the tanks next to it.
The heads are the hard part
- Gored stainless top head, cut in pie-shaped gores, dozens per head, crimped and screwed at each seam.
- Rigid phenolic insulation under the top head, pre-formed to the dished shape so it holds up underfoot.
- Shell jacket lapped over the head jacket at the top seam, so rain runs down and off the tank.
- Corrugated stainless shell jacket over fiberglass, installed in rings with the upper sheet lapped over the lower one.
- Stainless bands with wing seals around the shell.
- Sealed cut-around at every nozzle, manway, clip and lug, caulked to keep water out.
- Bottom head and legs, the lowest and most awkward work on the tank.
A dished head is the slowest part of a tank to insulate and jacket. On this tank, 28 of about 41 cut-arounds are on the two heads: manways, nozzles, handrail posts and pipe-support clips on top, and outlet nozzles and the four legs below. On the 2020 tanks, the heads took about half the labor.
The top head also gets walked on. Operators climb up to reach the manways and nozzles. In 2020 the heads were fiberglass under the stainless, and the fiberglass crushed underfoot. This time we specified rigid phenolic heads, pre-formed to the dished shape, so the gores lie flat and stay flat. The shell keeps fiberglass, at the thickness the specification calls for. That was 2 inch on the 2020 tanks and on this one.
Under the jacket, stainless wire holds the insulation: rings and radials on the heads, wraps on the shell. Every screw is stainless with a sealing washer, and every cut-around is caulked. On an outdoor tank, any water that gets in ruins the insulation.
Removal comes first on a spill job
When acid gets into the insulation, the old system is wet, corrosive and a waste stream. Before anyone prices it, settle three things:
- Who profiles and hauls the waste. On a chemical spill this is usually the plant's waste contractor, and the plant's environmental team decides how it is packaged.
- What PPE the removal crew wears. Removal is acid work: chemical suits, gauntlet gloves, splash goggles and a face shield, and respirators for a fit-tested crew. Installation, after the tank is cleaned and released, usually goes back to normal site PPE.
- What happens if the tank fails its inspection. After removal, the plant checks the tank and anything on it, such as existing heat trace. That can take a day or so, or it can find a problem that needs a repair crew first. Ask your contractor to price removal and installation as separate lines, so a failed inspection does not stall the whole contract.
Existing heat trace usually stays in place. We protect it during removal, and the plant decides whether it needs repair.
What drives schedule and price
- The heads. Count the openings and attachments on each head. That count drives labor more than square footage does.
- Gore fabrication. Gored heads can be bought from a jacket fabricator or cut in our shop before we mobilize. We price both ways at the specified gauge and compare.
- Material lead time. Pre-formed phenolic heads ship about 2 to 3 weeks after order. Order them at award, or the crew waits.
- Access. A tank this size needs a scaffold ring around the shell. Rental runs in 28-day periods, so quote the full duration up front. In 2020 a second rental period became a dispute.
- The bottom head. On this tank it sits less than 2 feet off the slab at its lowest point. Low, awkward work is slow work.
- Duration. In 2020 a crew of 2 to 4 insulated and jacketed two tanks from mid-July to late August.
What to send for a quote
- The tank drawing, or the nameplate diameter and height
- Photos of the existing jacket, heads and openings
- The plant insulation specification, including jacket gauge and finish
- What happened to the old insulation, and who handles the waste
- Whether scaffold is by the plant or by us
- The window the tank can be out of service
Frequently asked questions
Can I use aluminum jacketing on a chemical tank?
We do not recommend it. Acids and caustics attack aluminum, and a small drip can corrode it through. Stainless costs more but lasts, and most plant specifications for chemical areas require it.
Corrugated or smooth stainless on the shell?
Either can meet a plant specification. Corrugated is stiffer and hides small dents. Smooth is common on heads and small vessels. On a repair, we usually match the tanks next to it.
Why are the tank heads insulated with a different material?
People walk on the top head, and fiberglass can crush underfoot even under a stainless jacket. Rigid phenolic, pre-formed to the dished shape, holds up and keeps the gores flat.
Written by Chris Kelley from Bilt Rite Insulation's chemical-tank work at a Central Texas industrial plant in 2020 and 2026. Field detail from Ruben Zamora, BRI superintendent, who walked the tank and planned the system.