GB2537819A

GB2537819A - Calibration fluid container

Info

Publication number: GB2537819A
Application number: GB1506677.2A
Authority: GB
Inventors: Knight Jeremy
Original assignee: Endet Ltd
Current assignee: Endet Ltd
Priority date: 2015-04-20
Filing date: 2015-04-20
Publication date: 2016-11-02
Also published as: GB201506677D0

Abstract

A calibration fluid container 10 for fluid containment, the calibration fluid container 10 comprising a container body 12 formed from at least first and second mutually engagable container body portions 14, each container body portion 14 having an 5 internal surface 18 which defines an inner volume. The inner surfaces 18 of the container body portions 14 define a fluid chamber 38 having a smoothed and passivated contiguous chamber surface when in an engaged condition. The container 10 further comprises a fluid port 32 in fluid communication with the fluid chamber 38, the or each said fluid port 32 having a fluid-flow opening on the internal surface of the respective 10 container body portion 14. A method S100 of manufacturing such a calibration fluid container 10 is also provided.

Description

Calibration Fluid Container The present invention relates to a calibration fluid container, in particular to a sample cylinder for containing calibration gas mixtures for trace elements, ultra-high-purity fluids and samples. The invention further relates to a method of manufacturing such a calibration fluid container and to a method of reducing flow disturbance in a calibration fluid container.

Calibration fluid containers are used to contain fluid samples which can be utilised, for example, in metrology of trace elements, ultra-pure fluids, or fluids placed under extreme temperatures or pressures. The sample fluid in retained inside the calibration fluid container, acting either as a reservoir prior to passing to a sensing instrument, such as a cinematograph, or may be used to calibrate such a sensing instrument.

There are a few challenges to be overcome with respect to adequate calibration of ultra-high-purity gas samples. In the case of corrosive fluids, there can be an issue of contamination or corrosion of the joints of the calibration fluid container, particularly at or adjacent to valves controlling the flow of fluid to the calibration fluid container. This is a particular problem for screw-threaded joints, which typically use sealing compounds or tapes to stop leakage along the screw-thread pathway if the seal is not correctly formed so as to be fluid-tight.

Another concern relating to calibration fluid containers is the problem of sorption effects, including both absorptive and adsorptive effects, on the internal surfaces of the calibration fluid container. In particular, adsorption onto the inner surfaces of substances which are reactive with the fluid to be contained is a serious problem. This is highly significant if the calibration fluid container is to be used in connection with a plurality of mutually reactive substances.

Sorption effects can be minimised by treating the inner surfaces of the calibration fluid container, for example, by passivation of the surface, for example, by electropolishing. This smooths the metallic surface at the micro-and nanoscopic scale, limiting the ability of fluid molecules to adsorb onto the internal surface which could otherwise contaminate ultra-pure gas mixtures.

Sorption effects are also minimised by providing internal surfaces which are as smooth as possible, and smooth internal surfaces also minimise flow disturbance inside the calibration fluid container, leading to a smooth fluid flow through the system.

However, in order to minimise the number of joints required to form a calibration fluid container, the container is typically formed as a cylinder, thereby avoiding corners on the internal surface which increase sorption effects, which is either extruded or spun as a unitary piece of metal, inclusive of the fluid inlet and outlets. This results in an internal surface which is inaccessible from the outside of the cylinder, making techniques such as mechanical smoothing or electropolishing very challenging to perform to an adequate and verifiable standard.

It is an object of the present invention to provide a calibration fluid container which allows for the internal surface of the container to be smoothed and passivated easily, whilst eliminating the problems associated with having screw-threaded joints.

According to a first aspect of the invention there is provided a calibration fluid container for fluid containment, the calibration fluid container comprising: a container body formed from at least first and second mutually engagable container body portions, each container body portion having an internal surface which defines an inner volume, the inner surfaces of the container body portions defining a fluid chamber having a smoothed and passivated contiguous chamber surface when in an engaged condition; and one or more fluid ports in fluid communication with the fluid chamber, the or each said fluid ports having a fluid-flow opening on the internal surface of the respective container body portion.

By providing a calibration fluid container which is comprised of a plurality of container body portions so as to permit access to the internal surfaces of the calibration fluid container prior to assembly, it is possible to smooth and treat the inner surfaces, for example, using electropolishing or applying a passive coating Whilst doing so, it is still possible to maintain a smooth, contiguous surface at or adjacent to the joints, thereby limiting the likely sorption effects that would otherwise result. This beneficially allows for the manufacture of a calibration fluid container which is less likely to become contaminated due to said sorption effects, which might otherwise affect the accuracy of measurements taken downstream of the calibration fluid container, for example. This allows the calibration fluid container to be used for ultra-high-purity fluid sampling.

Ideally, the smoothed and passivated chamber surface may have a roughness of less than or equal to 0.40 microns, and more preferably has a roughness of less than or equal to 0.25 microns.

The smoothness of the chamber surface is critical in minimising flow disturbance and sorption effects, and the lower the surface roughness, the better.

The first and second container body portions may be provided as end cap container body portions, outlet said fluid port being provided in each of the end cap container body portions. Preferably, the or each said fluid port may be integrally formed as one-piece with the respective container body portion.

By providing two distinct end caps, each having either a fluid port, there is a definite fluid pathway defined through the volume of the calibration fluid container, allowing the calibration fluid container to be positioned in-line with an existing pipe manifold, for instance, whilst minimising the overall disturbance to the fluid flow therein. The two end caps could be directly engaged to create a fluid chamber having a relatively small volume.

In a preferred embodiment, there may comprise at least a further container body portion interposed between the first and second container body portions, said further container body portion having a further internal surface which is smoothed and passivated to define in part said fluid chamber.

A central container body portion or portions intermediate the end caps may be used to provide the majority of the internal volume of the calibration fluid container. It will be apparent that identical end caps could be used for a plurality of different sample cylinders, with different central container body portions being utilised in order to alter the dimensions of the calibration fluid container as a whole. This modularity advantageously reduces the overall cost to manufacture a plurality of containers of different internal volumes.

The internal surfaces of the container body portions may be mechanically smoothed prior to passivation, may be electropolished, and/or may be covered with a passive coating, such as a silicone-based coating.

Because the container body portions are separable, allowing access to the internal surfaces, machine tools can access the internal surfaces so as to be mechanically smoothed. The exposure of the internal surfaces of the container body portions prior to assembly of the final calibration fluid container allows for treatment of the internal surfaces. An expected use would be to passivate the internal surfaces in a manner which would not otherwise be possible for a calibration fluid container having a unitary container body, for instance, by the use of electropolishin2 or application of a passive coating.

An engagement interface of each container body portion may be formed as a flat perimeter surface, mutually co-operable with a corresponding engagement interface on another container body portion, the engagement interfaces being suitable for welding, preferably orbital welding. Similarly, an exterior end of the or each fluid port distal to the fluid chamber may be formed as a flat perimeter surface being suitable for welding, preferably, orbital welding, with which may be associated a fluid-control valve. In a preferred embodiment, the container body portions may be devoid of screw-threaded engagement portions, and/or the inner surface of the fluid chamber may be devoid of a screw-thread.

By providing clean, flat surfaces on the container body portions which are mutually compatible, it is possible to ensure that the components can be cleanly welded to one another, ensuring that the joints between component parts are robustly held together without leaks, whilst also maintaining a contiguous overlap between the inner surfaces of the container body portions which mi2ht otherwise increase adsorption of undesirable molecules. Providing a calibration fluid container which is completely welded together, the potential for fluid escape pathways through screw-threads is advantageously eliminated.

Optionally, there may further comprise a welding alignment element associated with at least one of the container body portions, which may have a square or rectilinear profile.

By providing welding alignment elements which allow the various container body portions to be clamped or otherwise gripped during the welding process, a calibration fluid container can he very accurately welded, for example, by orbital welding, whilst still readily maintaining a smooth cylindrical inner surface, which limits the sorption effects on the internal surface of the calibration fluid container.

The calibration fluid container may be provided in the form of a kit of parts, or may be provided as a fully-assembled unit.

According to a second aspect of the invention, there is provided a method of manufacturing a calibration fluid container with an inner surface of a fluid chamber being devoid of a screw-thread, the method comprising the steps of: a] providing a calibration fluid container, preferably in accordance with the first aspect of the invention; b] smoothing and passivating the internal surfaces of the container body portions; c] bringing the container body portions into contact at engagement interfaces thereof; and d] welding the engaged container body portions to one another to form a calibration fluid container.

By welding adjacent container body portions together to form a calibration fluid container, it is possible to eliminate many of the undesirable qualities associated with screw-threaded engagement, such as through incorrectly or incompletely engaged components. This is a particular issue where co-operating screw-threaded components arc over-tightened with respect to one another, since this can damage the screw threads and lead to fluid escape pathways from inside the calibration fluid container.

The passivation may be achieved by using electropolishing, and/or by forming a passive coating on the internal surfaces, such as a silicone coating which is applied to the internal surfaces. Optionally, there may further comprise a step subsequent to step d] of leak-testing the welding.

Since the internal surfaces of the container body portions are exposed prior to assembly of the calibration fluid container, it is possible to smooth and treat the internal surfaces, in particular to achieve passivation of the internal surfaces. This advantageously limits the degree to which sorption of undesirable molecules onto the internal surfaces can contaminate the fluid sample, which could feasibly result in undesirable reactions or inaccuracies creeping into measurements in a fluid pipe manifold which contains the calibration fluid container.

During step d], the welding may be performed via orbital welding. Additionally or alternatively, there may be a further step c] of providing at least one fluid-control valve engagable with the or each fluid port; and step f] of welding the engaged fluid-control valve to the or each fluid port. During step f], the welding may be performed via orbital welding. The method may also thither comprise a step g] subsequent to step f] of providing a cap element engagable with the or each fluid-control valve to protect the valve during transit.

Orbital welding of the joints between the container body parts ensures an even weld, resulting in minimal interference with the internal surfaces of the calibration fluid container during the assembly process. By also welding the fluid-control valves to the calibration fluid container, it is possible to further mitigate the deleterious effects associated with having screw-threaded engagement, whilst also providing a means of isolating the fluid chamber within the calibration fluid container; this feasibly allows each container to be transported having an inert fluid contained within the fluid chamber, reducing the likelihood of contaminative interaction with, for example, atmospheric gases. A cap element serves to further protect the valves in transit.

According to a third aspect of the invention there is provided a method of reducing flow disturbance in a calibration fluid container, preferably in accordance with the first aspect of the invention, the method comprising the steps of providing a multi-part container having inner surfaces which are smoothed and passivated to define a contiguous fluid chamber, at least one of the container parts having one or more fluid ports in fluid communication with the fluid chamber, the or each said fluid port having a fluid-flow opening on the internal surface of the respective container body portion.

By integrating the fluid ports of the calibration fluid container, rather than providing inwardly projecting fluid flow tubes, it is possible to minimise the disruption to effective fluid flow within the container, whilst also simultaneously minimising the sorption effects at the fluid port entrance to the fluid chamber.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a plan view of one embodiment of a calibration fluid container in accordance with the first aspect of the invention; Figure 2 shows a cross-sectional view through a central longitudinal plane of the calibration fluid container of Figure 1; Figure 3 shows a plan view of the calibration fluid container of Figure 1 in an assembled condition; and Figure 4 shows a diagrammatic representation of a method of manufacturing a calibration fluid container in accordance with the second aspect of the invention.

Referring firstly to Figures 1 and 2, there is shown a calibration fluid container, indicated globally at 10, for the containment of fluid samples, in particular ultra-high-purity fluid samples. Examples of such fluid samples might extend to high temperature or pressure acids or alkalis, explosive gases such as hydrogen or methane, or highly toxic and corrosive gases such as chlorine or fluorine. Calibration fluid containers therefore need to be able to withstand the rigours of transporting a wide-variety of such fluids.

The calibration fluid container 10 has a container body 12 which comprises a plurality of container body portions 14 interengaged to form the assembled container body 12. In the depicted embodiment, there are three container body portions 14: a central container body portion 14a and first and second end cap container body portions 14b.

It will be appreciated that the provision of three container body portions 14 is sufficient to create an elongate calibration fluid container 10 as depicted; however, any number or shape of mutually interengagable container body portions 14 could be provided. For example, only the first and second end cap container body portions 14b could be provided so as to create a far shorter calibration fluid container, or multiple central container body portions 14a could be provided so as to lengthen the calibration fluid container. The embodiment of the calibration fluid container 10 as depicted is therefore for illustrative purposes only.

The central container body portion 14a is formed as an elongate cylindrical tube 16 formed from a suitably unreactive metal, such as stainless steel, and has a, preferably cylindrical, inner surface 18a of uniform diameter along its longitudinal extent. The inner surface 18a of the central container body portion 14a thereby defines a cylindrical volume 20a therein.

On the external surface 22a of the central container body portion 14a is provided a welding alignment element 24a, which is here integrally formed with the external surface 22a of the central container body portion 14a, but could be releasably engagable therewith. The welding alignment element 24a is formed having a square or rectilinear profile for simple retention within a clamping device to enable steady welding, and a plurality of screw-threaded apertures 26 are also provided to both facilitate clamping and permit attachment of the assembled calibration fluid container10 to other objects.

Each of the end cap container body portions 14b is formed as a, preferably cylindrical, block 28 which is capped at one end by an outer wall portion 30, through which extends a fluid port 32, which can act as either a fluid inlet or fluid outlet, and is open at its other end. At the open end, the perimeter 34 of the cylindrical block 28 is flat and smooth, and is complementarily shaped to the perimeter 36 of the cylindrical tube 16 of the central container body portion 14a. The two perimeters 34, 36 thereby form an engagement interface with one another Whilst a fluid port 32 is illustrated at either end of the calibration fluid container 10, it will be appreciated that any appropriate fluid port to the inside of the calibration fluid container 10 could be provided. A single tube, acting as both fluid inlet and outlet could be provided, or a plurality of fluid inlets and/or outlets could also he provided.

The inner surface 18b of each end cap container body portion 14b at the open end is formed so as to flushly match the shape of the inner surface 18a of the central container body portion 14a, the walls of the inner surface 18b of the end cap container body portion 14b converging to form an internal dome adjacent to the outer wall portion 28, from which the fluid port 32 extends. The inner surface 18b thereby defines a capped cylindrical volume 20b.

As with the central container body portion 14a, there is a welding alignment element 24b affixed to the external surface 22b of each end cap container body portion 14b, within which are again provided a plurality of screw-threaded apertures 26. The threads can be seen in the cross-section of Figure 2. The welding alignment element 24b similarly has a square or rectilinear profile.

The complete modular calibration fluid container 10 is assembled as shown in Figure 3; one end cap container body portion 14b is engaged at either end of the central container body portion 14a. The combined inner surfaces 18a, 18b of the central container body portion 14a and end cap container body portions 14b are complementarily shaped so as to form a smooth, contiguous inner surface 18 for the calibration fluid container 10 as a whole, indicated by the dashed fines in Figure 3.

The inner surface 18 defines a fluid chamber 38 of the calibration fluid container 10, the volume of which is defined by the sum of the volumes 20a, 20b of the container body portions 14. This volume is preferably devoid of screw-threads, and is both smooth and passivated; this limits sorption onto the surface. whilst also reducing surface roughness which might disturb or interfere with fluid flow within the fluid chamber 38.

To secure the container body portions 14 so as to form the calibration fluid container 10 in its assembled state, the container body portions 14 are welded together along the respective perimeters 34, 36 of the individual central or end cap container body portions 14a, 14b. As the illustrated calibration fluid container 10 is largely cylindrical, the central or end cap container body portions 14a, 14b can be held in place using the welding alignment elements 24a, 24b and then orbital welded about the perimeters 34, 36. The container body portions 14a, 14b could feasibly be initially held in place using screw-threaded engagement prior to welding, but it is preferred that the container body portions 14 include no screw-threaded portions, with the exception of the screw-threaded apertures 26. Alternatively shaped calibration fluid containers 10 may need to be welded using different welding techniques, however.

The assembled modular calibration fluid container 10 therefore defines a complete fluid chamber 38 which has only two welded joints 40, and two fluid ports 32 leading therein, acting as fluid-flow openings into the fluid chamber, in case, a fluid inlet and a fluid outlet. In this instance, the fluid chamber 38 is substantially prolate.

The advantage of the calibration fluid container 10 as described over unitarily-formed sample cylinders is that, prior to assembly, the internal surfaces 18a, 18b of the central and end cap container body portions 14a, 14b can be mechanically smoothed, using physical machining tools, and subsequently passivated to limit the effects of sorption. This passivation would primarily be achieved using electropolishing, which involves the insertion of the container body portions 14 into an electrolyte to electrochemically smooth the internal surfaces 18a, 18b, the container body portion 14 acting as an anode in the electrochemical cell. Ideally, the internal surfaces 18a, 18b are smoothed so as to have a surface roughness of less than 0 40 microns, and preferably less than 0.25 microns, in order to minimise sorption effects.

Additionally or alternatively, the passivation could be achieved by the application of a physically and/or chemically inert, passive coating to the internal surfaces 18a, 18b, such as a silicone-based coating. One example of such a coating might. be a silicone-based coating such as SilcoNert 2000 RTM available from SilcoTek, 225 PennTech Drive, Bellefonte, PA 16823, USA; other similarly inert coatings are available. Other means of passivation of a metal surface will be apparent to the skilled reader, and the above-mentioned techniques do not represent an exhaustive list.

The calibration fluid container 10 may be supplied in its complete form, or as a kit of parts to be welded together. However, it may also be provided inclusive of one or more fluid control valves, such as the ball taps 42 illustrated in Figure 3. These taps 42 would typically have a passivated inner surface for use with aggressive fluids which might otherwise corrode the mechanisms of the taps 42, and are capable of either activating or deactivating flow control to the calibration fluid container 10. More complicated valves, which provide a degree of flow modulation, could also be considered, and many types and form of valve are known in the art.

In this instance, the taps 42 have a flat perimeter inlet 44 which is mutually compatible with an outer perimeter 46 of the fluid ports 32. This allows the taps 42 to be welded to the fluid inlet or outlet of the calibration fluid container 10, preferably using orbital 30 welding, which removes the need for screw-threaded connectors, which may otherwise result in leakage or contamination of the joints.

In a preferred method of forming the assembled modular calibration fluid container 10, indicated globally as 5100 in Figure 4, the container body parts 14 are provided at step S110. The internal surfaces 18 of each container body part 14 are then physically smoothed at step S120. Each container body portion 14 may then have its internal surface 18 passivated at step S130, preferably by a combination of electroplating and coating with a silicone covering, such as SilcoNert 2000 RTM. This renders the internal surface 18 highly resistant to sorption effects.

Once the internal surfaces 18 have been passivated and are ready to be connected, the respective container body portions 14 are brought into engagement at step 5140 at their perimeters 34, 36. At this point, the container body portions 14 can be held in place via the welding alignment elements 24a, 246, and the container body portions 14 can be welded at step S150 at the perimeters 34, 36, preferably via orbital welding to create a secure and uniform weld.

Depending on how the modular calibration fluid container 10 is to be provided, fluid-control valves 42 may be provided, which can also be welded in place at step S160 so as to be in engagement with the fluid ports 32 forming the fluid inlet and outlet.

Once the calibration fluid container 10 is fully assembled, the quality of the welding can be tested at step S170, with the joints 40 being leak-tested. If fluid-control valves 42 have been provided, then, prior to transit, it may be preferable to attach protective cap ekments at step S180 to the outwardly-facing ends of the fluid-control valves 42. The cap elements can be attached, releasably or otherwise, to the container body 12 in order to prevent accidental dislocation of the cap elements.

As previously discussed, there is no specific requirement for a cal bration fluid container to be formed as a cylinder, although a cylindrical or prolate inner surface which is smoothly curved will limit the potential for sorption to occur whilst minimising fluid-flow disturbance inside the fluid chamber. Consequently, it is generally accepted that from the perspective of manufacturing efficiency, the calibration fluid container should be externally cylindrical, thereby utilising the minimum amount of material to form the container. It will be apparent that any shape or arrangement of container body portions could be utilised in order to create the assembled calibration fluid container.

The present method of manufacturing a calibration fluid container also does not necessarily have to be used to passivate the internal surfaces of the container body portions. Any action which might need to be performed to the internal surface of the container prior to assembly would feasibly benefit from such a method of construction. For example, it may be desirable to etch the internal surface, or chemically activate the surface for catalytic uses.

It is therefore possible to provide a modular calibration fluid container for a fluid, in particular an ultra-high-purity fluid, a container body of which is formed from a plurality of discrete container body portions which are mutually engagable. This beneficially allows the user to treat the internal surfaces of the calibration fluid container prior to assembly, for example, allowing for the internal surfaces to be passivated with respect to sorption effects.

Furthermore, the container body parts may be welded together in such a manner so as to remove the need for screw-threaded joints, which can lead to routes for fluid egress, weakening the joints of the calibration fluid container and increasing the risk of sample contamination.

The words 'comprises/comprising' and the words 'having/including' when used herein with reference to the present invention arc used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity. described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.

Claims

Claims 1. A calibration fluid container for fluid containment, the calibration fluid container comprising: a container body formed from at least first and second mutually engagabk container body portions, each container body portion having an internal surface which defines an inner volume, the inner surfaces of the container body portions defining a fluid chamber having a smoothed and passivated contiguous chamber surface when in an engaged condition; and one or more fluid ports in fluid communication with the fluid chamber, the or each said fluid port having a fluid-flow opening on the internal surface of the respective container body portion.
2. A calibration fluid container as claimed in claim 1, wherein the smoothed and passivated chamber surface has a roughness of less than or equal to 0.40 microns.
3. A calibration fluid container as claimed in claim 2, wherein the smoothed and passivated chamber surface has a roughness of less than or equal to 0.25 microns.
4. A calibration fluid container as claimed in any one of claims 1 to 3, wherein the first and second container body portions are provided as end cap container portions, a said fluid port being provided in each of the end cap container body portions.
5. A calibration fluid container as claimed in any one of the preceding claims, wherein the or each said fluid port is integrally formed as one-piece with the respective container body portion.
6. A calibration fluid container as claimed in any one of the preceding claims, further comprising at least a further container body portion interposed between the first and second container body portions, said further container body portion having a further internal surface which is smoothed and passivated to define in part said fluid chamber.
7. A calibration fluid container as claimed in any one of the preceding claims, wherein the internal surfaces of the container body portions are mechanically smoothed prior to passivation.
8. A calibration fluid container as claimed in any one of claims 1 to 7, wherein the internal surfaces of the container body portions are passivated by electropolishing.
9. A calibration fluid container as claimed in any one of the preceding claims, wherein the surfaces of the fluid chamber are covered with a passive coating.
10. A calibration fluid container as claimed in claim 9, wherein the passive coating is a silicone-based coating.
11. A calibration fluid container as claimed in any one of the preceding claims, wherein an engagement interface of each container body portion is formed as a flat perimeter surface, mutually co-operable with a corresponding engagement interface on another container body portion, the engagement interfaces being suitable for welding.
12. A calibration fluid container as claimed in any one of the preceding claims, wherein an exterior end of the or each said fluid port distal to the fluid chamber is formed as a flat perimeter surface being suitable for welding.
13. A calibration fluid container as claimed in any one of the preceding claims, further comprising a fluid-control valve associated with the fluid port.
14. A calibration fluid container as claimed in any one of the preceding claims, wherein the container body portions are devoid of screw-threaded engagement portions.
15. A calibration fluid container as claimed in any one of the preceding claims, wherein the inner surface of the fluid chamber is devoid of a screw-thread.
16. A calibration fluid container as chimed in any one of the preceding claims, further comprising a welding alignment element associated with at least one of the container body portions.
17. A calibration fluid container as claimed in claim 16, wherein the welding alignment element has a square or rectilinear profile.
18. A calibration fluid container as claimed in any one of the preceding claims, provided in the form of a kit of parts.
19. A calibration fluid container substantially as hereinbefore described, with reference to Figures 1 to 3 of the accompanying drawings.
20. A method of manufacturing a calibration fluid container with an inner surface of a fluid chamber being devoid of a screw-thread, the method comprising the steps of: a] providing a calibration fluid container as claimed in any one of the preceding claims; b] smoothing and passivating the internal surfaces of the container body portions; c] bringing the container body portions into contact at engagement interfaces thereof; and d] welding the engaged container body portions to one another to form a calibration fluid container.
21. A method as claimed in claim 20, wherein the passivation is achieved using clectropolishing.
22. A method as claimed in claim 20 or claim 21, wherein the passivation is achieved by forming a passive coating on the internal surfaces.
23. A method as claimed in claim 22, wherein the passive coating is a silicone coating applied to the internal surfaces.
24. A method as claimed in any one of claims 20 to 23, further comprising a step subsequent to step d] of leak-testing the welding.
25. A method as claimed in any one of claims 20 to 24, wherein during step di, the welding is performed via orbital welding.
26. A method as claimed in any one of claims 20 to 25, further comprising a step e] of providing at least one fluid-control valve engagable with the or each fluid port; and a step f] of welding the engaged fluid-control valve to the fluid port.
27. A method as claimed in claim 26, wherein during step the welding is performed via orbital welding.
28. A method as claimed in claim 26 or claim 27, further comprising a step g] subsequent to step f] of providing a cap element engagable with the or each fluid-control valve to protect the valve during transit.
29. A method of reducing flow disturbance in a calibration fluid container as claimed in any one of claims 1 to 19, the method comprising the steps of providing a multi-part container having inner surfaces which are smoothed and passivated to define a contiguous fluid chamber, at least one of the container parts having one or more fluid ports in fluid communication with the fluid chamber, the or each said fluid port having a fluid-flow opening on the internal surface of the respective container body portion.