The aim of AS 1528: Stainless steel tubes and tube fittings for food processing and hygienic applications is to standardise hygienic tube and fittings for use in dairy, food and beverage manufacturing. It has been successful in maintaining the required food safety standards in Australia and New Zealand.
AS 1528 was first issued in 2001 and developed by an ASSDA group of stakeholders in the manufacture, supply, fabrication and use of stainless steel tube and associated fittings in the food manufacturing industries.
Changing industry practice, some existing errors, internal consistencies and expansion of sizes required a revision of the standard. The drafting journey to bring AS 1528 up-to-date began in 2015 and has been a challenge, but its successful outcome is significant for the industry and a testament to everyone involved.
The new edition of AS 1528 was published in four parts by Standards Australia in October 2019:
Part 1: Tubes
Part 2: Screwed tube couplings
Part 3: Butt weld tube fittings
Part 4: Clamp tube fittings
The revision of the AS 1528 suite of standards from the 2001 edition has brought the documents' technical coverage up to current practice and recognised the target industries in which hygienic tube is used. The suite is easier to understand and use, and facilitates verification of product compliance so that it achieves the required hygienic conditions.
What the revision achieved
The 2019 edition achieved all of the original aims, except one (see below). The suite of four standards now presents as a consistent coverage of all the tube and fittings regularly supplied in Australia.
- Addition of a consistent set of pressure ratings across all parts of AS 1528. Useful for designers.
- The wall thickness tolerance for tube has been changed. Previously it was +nil/-0.10mm for all sizes of tube. Widening it out to ±10% brings it into line with most other tube specifications and makes it more economical to manufacture without compromising product quality. It also then matches the tolerances of the fittings in other parts.
- The title now includes 'hygienic applications' in addition to food processing. This recognises the wider range of applications in which these products are already used.
- The reference to duplex stainless steels has been removed. In practice all tube and fittings referenced by these standards are austenitic.
- All tube and fittings can be produced without grit polishing the internal surface. Internal surface finish is specified by measurable roughness for hygiene cleanability.
- Inner tube surface roughness has been set as 0.8µm Ra maximum; this is consistent across all four parts of the standard and is also consistent with US and European specifications. From a gleanability perspective this is adequate. In addition there is now a specified maximum roughness for the inner weld bead, specified as 'Rt'. This is an unusual specification but it does address directly the requirement for cleanability of the remnant weld line.
- For the first time there is a stated limit for inner weld surface heat tint (no more than Level 3 in AWS D18.1M, commonly referred to as 'pale straw'). Again this aligns with US and European standards and much research work promoted by ASSDA and others.
- Consistent working pressures and temperature ranges have been given for all tube and fittings, with the exception of clamp fittings above 152.4mm.
- The range of sizes has been expanded generally up to 304.8mm or 12" diameter, but lesser maximum sizes for certain fittings, depending on market availability. Smaller diameter tubes have also been included as these have some niche applications. Additional wall thickness have been added. It is not anticipated that there will be a sudden move ways from the usual 1.60mm WT and the common OD range, but there were some industry requests for the expanded size range.
- Part 2 covering screwed couplings has been completely restructured. The two fundamental types - RJT and IDF/Trapezoidal - are clearly separated, with all dimensional specifications included in Sections 2 and 3. Section 1 deals with the requirements common to both types.
- Fittings not previously recognised have now been included. This includes both RJT blank hexagonal nut and an IDF blank cap in screwed couplings (AS 1528 Part 2). Butt weld fittings (Part 3) has addition of crosses, equal radius tees and 45 degree tees. In clamp fittings (Part 4) an end cap has now been included.
- The branch lengths of reducing tees and crosses (Part 3) have been clarified. The previous edition have a specification for this dimension that was in some cases contradictory and in all cases confusing. The new requirement is that the branch length, measured as the extension beyond the run surface, is the same as the branch OD.
- Reducers, both concentric and eccentric (Part 3), now include the option of a short extension to enable orbital welding.
- Reducers are now standardised as 'short reducers', with the 'full flow' reducers still specified but in the absence of request the standard type is short.
- New appendices in Part 4 cover a very useful description of clamp conditions for correct installation (App C), specification of grooves for expanded-type clamp liners (App D) and the method for expanding (App E).
- Correction of a long list of typos and inconsistencies in dimensions.
What was not achieved
The New Zealand market is already using AS 1528 and keen to have it branded as their own, but early discussions between the committee, Standards Australia and Standards New Zealand revealed the cost imposed by Standards Australia to make the project a joint cross-Tasman effort was prohibitive. As a result, the project became simply Australia, but the committee was able to co-opt a New Zealand member, and a tube manufacturer active in both Australian and New Zealand was also included as a Drafting Leader. The project therefore included New Zealand input, even though the document is branded Australian. The committee was mindful that there is substantial cross-Tasman movement of tube and fittings, of manufactured processing equipment, of engineering expertise and of food product, so joint output was essential to maximise all-round benefits.
Why this revision was important
The AS 1528 suite is the only fully integrated set of standards to the Australian industry's traditional dimensions for stainless steel tube and tube fittings for hygienic applications.
The Australian food manufacturing industry is critical both because of our high standards for domestic consumption and also as a very significant export earner. Australia has a clean and green reputation that only thrives if we can guarantee freedom from contamination.
All the commonly used and some niche tube and fitting products are covered and all are consistent.
Food manufacturing plant is getting bigger, so this edition includes provision of larger size tube and fittings. The applications are also increasingly diverse, so an expanded range of products is appropriate.
This revision presents manufacturers of tube and fittings with a clear, consistent and measurable standard for these critical products. The standard offers a pathway to economical outcomes for tube and fittings manufacturers, designers, installers and asset owners.
This article was written by Technical Consultant and AS 1528 Committee Chairman, Peter Moore.
This article is featured in Australian Stainless Magazine issue 68, 2020.