The AS 1528 integrated suite of standards (Stainless Steel Tubes and Tube Fittings for Food Processing and Hygienic Applications) was released for public comment last month. Chairman of the FT-027 Committee, Peter Moore, has kindly provided the below commentary for ASSDA Members to summarise the significant changes proposed in the revision of AS 1528 parts 1 to 4, dated 2001. The commentary is designed to be read in conjunction with the draft standards open for public comment, which close on 4 January 2019 (deadline extended from 26 December 2018).

To access the draft standards and submit comments, please click on the following link (you will find the links to the AS 1528 draft standards towards the the bottom of the table):


It will request you to log in to the 'Standards Hub' by either using your existing public or committee login. If you do not have one, it is simple to register and create a public user account. You do NOT have to separately get the draft(s) from SAI Global. Instructions on how to comment are provided upon log in. Please note, comments for each four parts of the AS 1528 standard must be submitted separately.

Commentary is provided as below.

All Parts

  1. The title now includes “hygienic applications” in addition to food processing. This recognises the wider range of applications in which these products are now already used.

  2. The reference to duplex stainless steels has been removed. In practice all tube and fittings referenced by these standards are austenitic.

  3. Inner tube surface roughness has been set as 0.8µm Ramaximum; This is consistent across all four parts of the standard and is also consistent with US and European specs. From a cleanability perspective it was believed this is adequate. 

  4. Consistent working pressures and temperature ranges have been given for all tube and fittings, with the exception of clamp fittings above 152.4mm. 

Part 1 (Tube)

  1. The main change is the wall thickness tolerance. This was previously set at +0/-0.10mm, a highly unusual and unnecessarily tight tolerance. Opening the tolerance out to the more usual ±10% gives the tube manufacturers more scope for economical strip purchase without compromising application or fabrication; This tolerance matches those of the matching fittings.

  2. The range of standard sizes has been expanded down to 6.35mm and up to 304.8mm OD (12”) and wall thicknesses established as standard now include a range from 0.9mm to 3.0mm, not just a single WT (previously 1.6mm for all sizes except for 2.0mm at the previously upper OD of 203.2mm). It is not anticipated that there will be a sudden move away from the usual 1.6mm and the common OD range, but it was believed that there is some industry need for the expanded size range.

  3. A small change has been made to clarify the length tolerance.

  4. There is now a specified maximum roughness for the inner weld bead, specified as an “Rt”. This is an unusual specification and the committee is particularly interested in any viewpoints on this.

  5. For the first time there is a stated limit for inner weld surface heat tint. Again this aligns with American and European standards and much research work.

Part 2 (Screwed Tube Couplings)

  1. The main change is a complete re-structuring to make the standard more easily referenced. 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.

  2. Guides for expanding both types are retained, but the guide for welding was considered redundant as this is adequately covered elsewhere and has been removed.

  3. An RJT blank hexagonal nut has been added, as has an IDF blank cap. 

  4. All dimensions and particularly tolerances have been reviewed and many have been revised for consistency.

  5. Two alternative designs are given for orbital welding of welded-type liners.

Part 3 (Butt Weld Tube Fittings)

  1. The range of sizes has been increased up to 304.8mm for the products where these are in fact now available.

  2. Nominal wall thicknesses for these larger sizes now include the options for 2.0, 2.5 and at the top end 3.0mm.

  3. The standard makes it clear that bends are supplied with straight-end extensions as standard, and other fittings are supplied without. The opposite options are set as available but only “if requested”.

  4. The branch lengths of reducing tees and crosses have been clarified. The previous edition gave a specification for this 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.

  5. Cross fittings, equal, reducing and pulled, have been added. 

  6. Equal radius tees have also been included for the first time.

  7. 45° Tees have also been added for the first time.

  8. Y-pieces have had their dimensions corrected (an error in the previous 2001 edition) and now more comprehensively dimensioned.

  9. “H” dimensions – a measure of the overall height of the fitting – have been included for the first time. This dimension is very simple to measure without complex metrology equipment and may be of more use in the real world than centre-to-end dimensions.

  10. Reducers, both concentric and eccentric, now include the option of a short parallel extension to enable orbital welding.

  11. Reducers are now standard as “short reducers”, with the “full flow” reducers still specified but in the absence of request the standard type would be short.

  12. Reducer dimensions are now fully detailed in a table.

  13. A full review of dimensional tolerances has resulted in a comprehensive tolerancing table.

Part 4 (Clamp Tube Fittings)

  1. An end cap has been added.

  2. The range of sizes has been increased up to 304.8mm and down to 6.35mm for the products where these are in fact now available.

  3. A “Type A” groove detail has been included for 6.35 mm to 19.05 mm OD fittings.

  4. A “Type C” gasket has also been added for these very small sized fittings.

  5. New appendices 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).

Thank you for your support of ASSDA, and we encourage all those involved to contribute your feedback and expertise in the review of the AS 1528 suite of standards.

If you require assistance or have any questions, please do not hesitate to contact our Technical Specialist Graham Sussex directly: 
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