Find out about:
what constitutes a pressure vessel (with a focus on pressure vessel hazards),
design registering and design verification of pressure vessels,
and owner responsibilities, including pressure vessel registration as an item of a plant.
Ins and outs of pressure vessel regulation
By: HYDAC National Development Manager for Industrial Hydraulics Ali Nejat.
Mr Nejat is also a mechanical engineer with over 15 years’ experience in the fluid power industry as well as being a certified pressure vessel inspector
What constitutes a pressure vessel?
The first thing that a customer wants to know is whether their vessel is characterised as a pressure vessel.
The standard for pressure vessels is AS/NZS 1200, keeping in mind there are numerous different standards and definitions defining whether a particular vessel is categorised as a pressure vessel or not.
The general definition though is that a pressure vessel is subject to either internal or external pressure, including all its interconnected parts and components, gauges, and other fittings all the way up to the connecting piping.
This is quite broad terminology and doesn’t indicate whether the vessel is a pressure vessel subjected to a few bar as opposed to a vessel which is subjected to a 400 bar pressure.
This brings us to the AS 1210 design code for pressure vessels. This code provides a visual numerical method to define whether a particular vessel is a pressure vessel or not and whether it is to be considered as a controlled vessel or not.
Ultimately, however, it comes down to how hazardous a particular vessel is.
Focus point: how hazardous is the vessel?
All the regulations pertaining pressure vessels are divided into regulations and standards under the Work Health and Safety Act. Regulations revolve around Work Health Safety Regulations and standards around approved codes of practice and those applicable to pressure vessels.
Health and Safety Regulations at WorkSafe and WorkCover websites provide the governing rules in sections focused on fishing vessels. Then there is an array of different standards governing pressure vessels, with the first and foremost being AS/NZS 1200 – a standard that sets out some basic requirements and good practice for the design, material, manufacture, examination, testing, installation, conformity assessment, and other factors applicable to pressure vessels.
And then, as already mentioned, there’s AS 1210 which sets out the requirements for welding, pressure testing, and material in the form of a design code.
This provides a pressure vessel designer with information as to what material to select from a particular standard, thickness calculations, safety factors and other design-related subjects.
AS 4343 sets out guidelines and numerical methods to calculate the hazard level of a pressure vessel in parameters such as pressure (design pressure and not operating pressure), desired temperature, vessel volume in terms of pressurised fluid or substance contained, and the area in which the vessel is located.
The standard sees location at a refinery as a major hazard because an explosion will not only pose a threat to the vessel but other parts of the plant via a ripple effect. Also, a pressure vessel buried in the ground is seen as less dangerous than a pressure vessel situated in a refinery.
AS 4343 delineates the different substances that can be contained by a pressure vessel, with a vessel subject to pressurised water being less hazardous than one subject to a corrosive and potentially lethal substance or operating at a lethal temperature.
Also important are pressure vessel inspection standard AS/NZS 3788 and quality assurance around manufacturing procedures standard AS 3920.
Design registering of pressure vessels
All pressure vessels distributed by HYDAC are design registered.
As to pressure resources that don’t have any compliance in place, it all comes down to their hazard level and whether or not design registration is required.
In this regard there is a national occupational health and safety (OHS) standard by the name of the NOHSC:1010. Schedule 1 stipulates that a pressure vessel of a higher hazard level of A, B, C, D out of five different categories (A,B,C,D,E) must have its design registered and the hard stamp holder’s design registration information on that vessel.
Typically the registration process is executed prior to the manufacture of the vessel because first and foremost it is important to ensure that the design is in fact compliant with the requirements of a particular code chosen as the design code.
Design and design verification of pressure vessels
The designer of a pressure vessel in Australia would first ensure that the vessel’s material, its thickness, diameter and safety devices etc. are in accordance with AS 1210.
Following this they would set out the basis of their calculations on an engineering drawing, which would typically entail writing down the design code of the vessel, its hazard level, design pressure and volume level among other design parameters relating to procedure.
AS 3920 gives a certified quality company such as HYDAC permission to execute the design verification, which is an essential part of the design registration process. This standard permits the design verification internally for pressure vessels with hazard level C and D. Anything higher such as A or B requires engaging a third-party independent design verifier for design verification.
In this regard the design verifier gets the desired code – AS 1210 – and the customer’s calculations and drawings, which they cross-reference. If the customer has done a good job in designing the vessel in accordance with the standard they award him a certificate of conformance or a design verification certificate.
The drawing and verification certificate are then sent to a regulatory authority such as WorkSafe or WorkCover for cross-checking in order to obtain a design registration certificate with a registration number (unique reference) on it.
The mandate for these authorities is only an engineering review, with their primary task being to ensure that someone in Australia can be held accountable for the design of the pressure vessel and its verification.
All the parameters from design pressure to design temperature together with the registration number are hard stamped on the body of the pressure vessel. From there the vessel can be manufactured, with all necessary information stamped onto it. In this way a customer can know that the vessel they receive is fully compliant.
An accumulator purchased from HYDAC with a compliant design can be likened to a car: as the car can’t be driven on the road until it has a registration plate so too the accumulator can’t be used until it has been registered as an item of the plant.
Some states such as Victoria made exemptions some years ago which make it unnecessary to register an item of a plant.
Typically though the owner of a plant or the owner of the pressure vessel has to get a pressure vessel registered as an item of the plant through obtaining documentation such as the manufacturer’s data report and design registration letter for online portals such as WorkSafe.
This makes for full traceability and transparency from a vessel’s identification number to its exact location – in fact everything that pertains to it.
HYDAC ensures that all its pressure vessels come complete with the required regulatory documentation.
The real work happens once the owner takes possession of the vessel in that they have to tick many boxes from knowing the item of the vessel to ensuring that planned registration and commissioning inspections as well as routine inspection have been completed. And it doesn’t stop there, with other inspections necessary further down the track.
They have to ensure that they have the correct document archiving processes in place for inspection and that they engage procedure inspectors at recommended intervals for periodic inspections to make sure the vessel is intact.
If the owner is confident about the procedure they can opt to do inspections on their own, keeping in mind that they will be held responsible for the integrity of that particular vessel.
The responsibility also lies with the owner to ensure that the vessel does not impose any risk to life or property.