How much colour change is normal after two years?

Answer: ΔE 9.3 on an orange lid and 4.6 on a grey shell are the medians. Report visible parts at ΔE 3, replace at ΔE 6, and stop once grade 2 chalking appears.

How many outdoor years does 1000 h of xenon cover?

Answer: About 2 years, or 21 months with the 0.9 factor for a humid bank, and only at 0.51 W/m² and 65 ℃ black panel.

How often should the gasket be replaced?

Answer: A new strip reads 28% compression set, the exposed ones 34%, leaving 6 points before the 40% limit, so 24 to 30 months is typical.

What if a bracket bolt has seized?

Answer: Soak it in penetrant for 12 h, then work it under 6 N·m instead of forcing 21 N·m. An insert that spins means the bore has cracked.

Does algae need clearing at every visit?

Answer: No. While the drains flow, algae never reach the lip, so 90 days is enough, plus one pass after a flood when silt loads run 5× higher.

Hydrology Case: Hydrology Monitoring Case

Quick answer: A hydrology case left on a river bank for 18 months reached ΔE 6.8 on its orange lid, against only 5.9 after 1000 h of xenon light.

The first evidence after 18 months
UV ageing in xenon hours
Long immersion and wet-dry cycling
Galvanic corrosion at the bracket
Algae, silt and annual service
FAQ

1. The first evidence after 18 months

Twelve hydrology case units were split in two: six bolted to concrete piers 1.6 m above normal water with lids tilted 15° south, six kept indoors as controls. After 18 months the exposed orange lids read ΔE 6.8, the grey shells 3.1 and the controls 1.2, taken at D65 and 8° with five points per shell.

Months	Orange lid ΔE	Grey shell ΔE	60° gloss	Shore A
0	0	0	100%	72
18	6.8	3.1	68%	76
24	9.3	4.6	54%	78

ΔE 3 is the first line for visible parts, where the eye begins to separate two same-colour faces, so 6.8 means lid and shell read as two colours. The grey shell ran at half the rate, because orange pigment absorbs weakly at 340 nm and UV reaches deeper.

2. UV ageing in xenon hours

The xenon test runs the ISO 4892-2 cycle, 102 min dry plus 18 min spray, 0.51 W/m² at 340 nm and 65 ℃ black panel. At 1000 h the orange lid read ΔE 5.9 against 6.8 outdoors, inside the usual ±15% band, so 1000 h converts to 2 years and a humid bank takes a 0.9 factor.

Hydrology case sample open on grey backdrop, egg-crate foam in the lid, cut compartments holding a flat black unit and coiled cables

The stabiliser package decides whether that conversion holds. Dropping HALS from 0.3% to 0.15% pushed ΔE from 6.2 to 11.4, while raising the UV absorber from 0.25% to 0.35% recovered only 1.1.

Wall thickness consumes stabiliser too. Thinning the lid from 3.2 mm to 2.8 mm removes 12% per unit area and lifts ΔE at 1000 h from 5.9 to 7.1.

Three thresholds apply: ΔE 3 to report a visible part, ΔE 6 to replace a structural part, and ISO 4628-6 grade 2 chalking to replace at once.

3. Long immersion and wet-dry cycling

River level swings 2.4 m a year, the lower edge of each shell sits 0.5 m above the highest flood mark, and 90 to 120 days fall in the splash zone with 1 to 3 wet-dry cycles a day. The first part to fail is the gasket groove, where water cannot drain and the EPDM strip sits at 25 ℃ to 33 ℃ all year.

Part	Material	24 h uptake	State at 18 months	Limit
Shell	Modified PP	0.03%	No swelling	None
Lid rib	PA66-GF30	1.8%	Bulge 0.2 mm	Above 0.5 mm
Gasket	EPDM 70 A	0.6%	Set 34%	Above 40%
Insert	Brass	—	White corrosion	When seized
Bracket	Q235, 65 μm zinc	—	Down to 48 μm	Below 40 μm

Compression set is the comparable figure: a new strip reads 28% after 72 h at 70 ℃, the exposed units 34% at 18 months against a 40% limit, and squeeze falls from 25% to 18% in two years.

Water enters by three routes: a gasket lip lifted 0.1 mm by silt, a blocked drain backing water 2 mm over the lip, and an insert that separates 20 μm from the shell after 60 thermal cycles.

4. Galvanic corrosion at the bracket

The bracket joint is the detail reports skip: hot-dip galvanised Q235 at 65 μm, a 304 stainless M8 bolt, and a PA66-GF30 shell loaded through a brass insert. Once a wet film links all three, the 0.15 V between stainless and brass drives a cell that consumes the insert.

Hydrology case units on a stepped wood display plinth, black and orange upright trolley cases behind, black flat cases in a row in front

At 18 months the bores held white zinc salt mixed with copper green, threads had seized, and breakaway torque had risen from 8 N·m to 21 N·m. Two inserts spun with the bolt and tore 0.4 mm cracks, so those units were scrapped.

Three fixes: 316 inserts, molybdenum disulphide grease on the bolt, and a 1 mm nylon washer to break the couple. Torque is then capped at 6 N·m and checked every 12 months, still holding 5.5 N·m at the fourth teardown.

5. Algae, silt and annual service

The lid channel is 3 mm deep with one 4 mm drain hole at each corner, and river silt runs 0.05 to 0.3 mm, so one flood can block two holes. Water standing 3 days is enough for algae to sheet across the channel and the gasket lip.

Never clean it with a wire brush. A scratch deeper than 0.1 mm across the 0.8 mm lip becomes a leak path worse than the algae; use a soft brush, then a flush to confirm the drain empties within 10 s.

Service task	Interval	Tool	Pass mark
Clear drains	90 days	4 mm pin	Empties in 10 s
Clean groove	90 days	Soft brush	No grit
Check squeeze	180 days	Caliper	≥18%
Teardown threads	12 months	Torque wrench	≤6 N·m
Re-measure ΔE	12 months	Colour meter	≤6
Measure coating	24 months	Coating gauge	≥40 μm

Three lid openings across 12 screws make 36 teardowns; grease after each and the fourth should rise by no more than 1 N·m, flagging seizure earlier than any visual check.

Conclusion

Match each service action to a design number and the life of a hydrology case becomes predictable. Drains every 90 days answer a 3 mm channel and 0.3 mm silt; squeeze checks every 180 days answer 34% set against a 40% limit; thread teardowns every 12 months answer a 0.15 V couple and 21 N·m of seizure. Three things belong on the drawing: HALS at 0.3% or above, 316 inserts, and 25 μm of coating margin. Do those and the sheet drops from six tasks to four, cutting a visit from 2.5 h to 1.5 h.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.