PSSR 2000 · Pressure systems

Blowdown vessel examination under PSSR

Independent examination of your blowdown vessel under a Written Scheme of Examination, by a competent person under PSSR.

Every time a steam boiler blows down it dumps scalding, pressurised water and sludge, and the blowdown vessel takes that shock, cools the water and vents the flash steam safely to atmosphere. The repeated thermal and pressure shock wears it from the inside, which is why it is examined alongside the boiler.

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  • Independent and impartial
  • Competent engineer surveyors
  • Reports issued promptly
Serves the boilerTakes the hot, pressurised blowdown from your steam boiler
Flash steamVents to atmosphere through a vent that must stay clear
Written schemeExamined as part of the steam boiler system
Certified reportA written report of examination, within 28 days
Pressure equipment we examine

Why your blowdown vessel needs PSSR examination

A blowdown vessel receives the bottom blowdown from a steam boiler, the hot, high-pressure water and sludge driven out to remove the dissolved solids that would otherwise damage the boiler. Inside the vessel the pressure drops, part of the water flashes to steam and vents to atmosphere, and the cooled water and sludge settle and drain away. The blowdown enters through a tangential inlet, and the swirling, flashing discharge erodes the shell at that point over time.

The vessel is part of the steam boiler installation and is examined under PSSR alongside it, to the written scheme that covers the boiler system. The examination looks hardest at the inlet and its wear plate, at the vent that must always be able to clear the flash steam, and at the shell for the thermal and pressure fatigue that repeated blowdowns bring. We examine it independently and report to the scheme.

Shell and welds
Tangential inlet
Inlet wear plate
Vent to atmosphere
Dip pipe and water seal
Drain and outlet
Isolation valves
Nameplate and SWP
How it works

How we examine your blowdown vessel

A competent engineer surveyor examines the vessel inside and out, with the inlet and its wear plate the first concern, because that is where the flashing blowdown erodes the steel. The vent is checked so it can always clear the flash steam and the vessel cannot pressurise, the dip pipe and water seal are checked, and the shell and welds are examined for the cracking that thermal and pressure cycling cause.

  • 1

    Get in touch

    Tell us the boiler and its blowdown vessel, and whether a written scheme for the system is in place.

  • 2

    On-site examination

    A competent engineer surveyor examines the vessel inside and out, the inlet, vent and shell, to the scheme.

  • 3

    Your report

    You receive a written report of examination, any defects and timescales set out, within the statutory window.

Why businesses choose SEIS

  • Independent and impartial: we examine the vessel, we do not supply or service it
  • Competent engineer surveyors used to steam boiler plant and PSSR
  • Internal and external examination of inlet, vent and shell, not a walk-round
  • Certified reports issued promptly, the next examination date flagged
What we examine

Blowdown vessel: what a thorough examination covers

Tangential inlet and erosion

The inlet where the flashing blowdown enters and swirls, examined for the erosion that wears the shell away at that one point faster than anywhere else.

Inlet wear plate

The wear plate fitted inside at the inlet to take that erosion, checked for condition and security, because once it is gone the shell itself is in the firing line.

Vent to atmosphere

The vent that carries the flash steam away, checked so it is clear and adequate, since a blocked or undersized vent is what lets a blowdown vessel pressurise dangerously.

Shell and welds

The shell and welds examined for the cracking and fatigue that repeated thermal and pressure shock bring, the slow damage of every blowdown over the years.

Dip pipe and water seal

The dip pipe and the water seal that keep cooler water in the base to temper the next blowdown, checked so the vessel does its cooling job and the discharge stays safe.

Drain, outlet and isolation

The drain, outlet and isolation valves checked for condition and security, including the protection that stops one boiler discharging into another during maintenance.

Scheme and certification

How it works, and what you receive

A blowdown vessel is part of the steam boiler installation, and where that system is in PSSR scope it is examined to the written scheme that covers the boiler, under Regulation 8 and Regulation 9. It is examined to the intervals the scheme sets, alongside the boiler and its mountings. After each examination you receive a written report on the condition of the vessel, with any actions and timescales, issued within twenty-eight days.

Step oneA Written Scheme of Examination, certified before use
To schemeExamined to the intervals the scheme sets
28 daysA written report, issued within the statutory window
IndependentWe examine it, we do not supply it

You receive a report on the condition of the system and its safety devices, with any actions and timescales set out clearly.

Full statutory cover

Part of our full PSSR inspection service

Blowdown vessel is one of the many kinds of equipment we cover. We inspect the full range, across every sector, as an independent provider, one item or a whole site, anywhere in the UK.

See our full PSSR inspection service
Other services

Other statutory inspections we carry out

Many sites run more than one regime. We can examine all of it, under one independent provider.

LOLER inspectionThorough examination and certification of lifting equipment and accessories. PUWER inspectionInspection of work equipment against the five PUWER duties, with a written record. LEV testingLEV thorough examination and test of your extraction systems.
PSSR FAQs

Blowdown vessel examination: common questions

Does a blowdown vessel need a PSSR examination?
As part of the steam boiler system, yes. The blowdown vessel takes hot, pressurised blowdown and flash steam from the boiler, so it is examined under PSSR to the written scheme that covers the system. You can read the duty in the HSE guidance on the Pressure Systems Safety Regulations.
Is it covered by its own written scheme, or the boiler's?
The written scheme for the boiler system should cover the blowdown vessel as part of that system, because it forms part of the pressure system the boiler serves. Regulation 8 requires that scheme before the system is operated. Our guide to PSSR explains what the scheme has to contain.
What wears out a blowdown vessel?
Erosion and thermal shock. The flashing blowdown swirling in through the tangential inlet erodes the shell at that point, and the repeated cycle of hot, pressurised discharges fatigues the shell and welds, which is why the inlet, the wear plate and the welds are examined closely.
Why does the vent matter so much?
Because the vent is how the vessel stays safe. A blowdown vessel relies on venting the flash steam freely to atmosphere rather than on a relief valve, so if the vent is blocked or undersized the vessel can pressurise. The examination checks the vent is clear and adequate for the flash it has to pass.
How often should it be examined?
To the intervals the written scheme sets for the boiler system, so it is normally examined alongside the boiler. The competent person sets and reviews those intervals on the duty and condition of the plant.
Who is competent to examine it?
A competent person with the training, skills, experience and knowledge for steam boiler plant, independent of its operation. Our engineer surveyors examine boilers and their blowdown vessels together and report to the written scheme.
Can you examine it at the same time as the boiler?
Yes, and that is usually the sensible approach. The blowdown vessel is part of the boiler system, so examining it during the same shutdown keeps the plant on one scheme and one set of dates rather than two.
Do you examine blowdown vessels across the UK?
Yes. Our engineer surveyors travel to boiler houses and plant rooms nationwide and work around your shutdown. Call 0330 043 8191 to arrange a visit for the boiler and its blowdown vessel together.

Is your blowdown vessel due an examination?

Talk to an engineer surveyor, get a quote and book your inspection anywhere in the UK.

0330 043 8191 Request a quote