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Download Technical Bulletin (July 2002)

Stainless steel is widely used in and around swimming pools and performs exceptionally well in most applications. Handrails and other fixtures are strong, durable and look attractive. They are easy to keep clean, and require little or no maintenance for the life of the pool.

However, some common types of stainless steel are not suitable for use in the airspace of indoor pool buildings in certain applications where they are subject to a tensile stress. In these circumstances a phenomenon known as stress corrosion cracking (SCC) can occur, with potentially tragic consequences.

SCC occurs under a unique set of circumstances found in the airspace of indoor pool buildings where the pool is sanitised with chlorine. Research into SCC does not suggest that outdoor pools are affected.

ASSDA has prepared the following advice to assist those who design and manage indoor pools to avoid the danger of SCC.

What is Stress Corrosion Cracking (SCC)?

Stress corrosion cracking causes microscopic cracks in the stainless steel, eventually resulting in failure. It is particularly dangerous because it can cause collapse without warning. It can only affect stainless steel under tensile stress, that is, elements such as fasteners, rods or wires which are supporting a load or from which a load is suspended. Residual fabrication and welding stresses can also cause vulnerability to SCC.

SCC is triggered by attack from corrosive chemicals present in the atmospheric conditions of indoor pools, which can occur even at room temperature.

The SCC failure mode can occur in most metals under particular conditions of stress and corrosive attack. Stainless steels are no exception, and when SCC failure occurs there is no obvious warning.

ASSDA strongly urges pool designers, owners and managers to take preventive action to avoid injury to pool patrons, by not using potentially susceptible stainless steel grades in load-bearing applications in pool buildings.

What Causes SCC in Pool Buildings?

In warm, humid conditions, chlorine reacts with ammoniacal body products to form volatile chloramines. Gaseous chloramines permeate the pool building and are absorbed by condensation in the cooler parts of the building, typically settling on structural components high up in the building's airspace. As the condensation evaporates, chloramines concentrate, becoming more aggressive.

Under these conditions, stainless steel may be corroded, and members in tension may suffer SCC. Catastrophic failure of the member may result, and the load it was supporting may fall. The problem is particularly likely to occur in the newer leisure centre type complexes, where the pool is kept at relatively high temperatures. There is often also intensive use, requiring higher rates of chlorine dosing to disinfect the water.

Where ozone disinfection is the only method of disinfection used, the warnings in this bulletin do not apply as failure by SCC is unlikely. However, SCC may be a threat where a back-up chlorine system is in place.

ASSDA strongly urges pool designers, owners and managers to take preventive action to avoid injury to pool patrons, by not using potentially susceptible stainless steel grades in loadbearing applications in pool buildings.

What is Affected by SCC and How Can it be Prevented?

SCC only happens in the airspace of indoor pools and only where chloramines accumulate on stainless steel elements which are under tensile stress. The vast majority of typical swimming pool components are unaffected. SCC does not affect stainless steel components which are immersed or regularly drenched, or which aren't under tensile stress, such as:
> benches
> pool ladders
> safety rails
> doors and windows.

SCC has not been found to be a problem in these applications. As SCC only occurs under a specific set of conditions, it can be effectively controlled through careful pool design (including ventilation) and stainless steel grade selection coupled with appropriate management of bather load and water conditions.

The grades of stainless steel which are known or suspected to be susceptible to SCC in these conditions are the common "18/8" grades such as 303, 304 and 316. Not enough is known about duplex grades such as 2205 to recommend them in this environment.

The typical fittings at risk are those holding up:

  • light fittings
  • air conditioning ducts
  • signage
  • wall/ceiling panels
  • suspended ceilings.

Stainless steel rigging and bracing are also vulnerable to SCC. All these elements should be specified in grades suitable for safety-critical use, such as 904L or a super-austenitic 6% Molybdenum alloy.

Ongoing measures for avoiding SCC risks include:

  • monitoring and controlling pool chemical levels
  • preventing excessive bathing loads
  • providing good shower and toilet
  • facilities and clear instructions to patrons
  • monitoring and controlling air quality
  • instituting a regular inspection and cleaning program as outlined below.

Inspection and Cleaning Regime

An inspection program should be instituted as a first step. ASSDA recommends that pool owners and managers compile an inventory of stainless steel parts which may be at risk of SCC and engage a qualified engineer to undertake assessment which may include:

  • cleaning
  • visual examination at X10 magnification
  • flexing wires or clips
  • tightening and loosening fasteners.

A dye penetrant test is also an option.

Typical indications of SCC are brown stains on the stainless steel but these can be inconclusive. If discolouration is found in a load-bearing, safety-critical location in the complex, samples should be tested for SCC. If a positive result is returned, it may be necessary to replace the affected components.

Expert advice should be sought to establish a course of action. A cleaning and inspection regime should be put in place and scheduled no less than twice a year. Thorough cleaning using plenty of fresh water is needed to remove chloramine deposits.

Simply wiping with a moist cloth is not sufficient. Strict adherence to such a cleaning and inspection regime will reduce the risk of SCC but no assurances can be given that the risk will be eliminated. Cleaning after cracks have commenced will not rectify the damage and components should be replaced immediately with a higher alloy stainless steel or another material.

Important Qualification
The technical recommendations contained in this Technical Alert are necessarily of a general nature and should not be relied on for specific applications without first securing competent advice. Whilst ASSDA has taken all reasonable steps to ensure the information contained herein is accurate and current, ASSDA does not warrant the accuracy or completeness of the information and does not accept liability for errors or omissions.

Download Technical Bulletin (July 2002)

Download Technical Bulletin (Revised June 2012)

Hydrofluoric acid is an aggressive substance used in the stainless steel industry, usually to assist in removal of scale and the chrome depleted layer associated with welds.

Changes in the National Drugs and Poisons Schedules have recently brought hydrofluoric acid (HF) into focus.

Products containing HF in concentrations greater than one percent (1%) now attract a National Drugs and Poisons Schedule 7 listing. In many states this has implications for license and permit requirements. Further information on the background to rescheduling of HF from a Schedule 6 to a Schedule 7 poison, can be found at the National Drugs and Poisons Schedules Committee website.

The implications of this change for people purchasing and using "pickling pastes" (usually incorporating HF at concentrations between 3% and 5%) and other pickling materials containing HF, and for persons selling these materials, are briefly described below on a state by state basis. The descriptions are based on verbal and in some cases written discussion with the departmental office in each state or territory and are not provided as definitive statements on your responsibilities. Also included are contact details for Public Health Authorities in each state. If you use or trade HF-containing products, ASSDA strongly suggests you contact state authorities for further information, licence applications etc.

ASSDA made representation to the National Drugs and Poisons Scheduling Committee which ultimately led to a change in the regulatory requirements in New South Wales. This change is reflected below.

It is likely however that there are conditions which must be met right now to buy or sell HF products in most states. Although in some cases licenses and permits are inexpensive, there is still paperwork to be completed and additional checks to be implemented in organisations handling these products.

Failure to comply with these laws may trigger various legal alternatives open to state authorities. Failure to obtain the relevant license or permit may also have implications for an organisation's insurance cover or other risk management arrangements.

ASSDA urges you to examine your responsibilities and maintain compliance with appropriate laws.

AUSTRALIAN CAPITAL TERRITORY (ACT)
Pharmaceutical Services, Health Protection Service, ACT Government Health

t: 02 6205 1700
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.health.act.gov.au

Sellers or manufacturers of Schedule 7 poisons require a license, issued by the Minister (of Health), to possess a Schedule 7 substance. The current license fee is from $322 per year. Schedule 7 substances must be securely stored at all times and any sales must be recorded in a poisons register.

NEW SOUTH WALES (NSW)
Pharmaceutical Services Branch, New South Wales Health

t: 02 9879 3214
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.health.nsw.gov.au

Purchaser is required to obtain and/or use an "Authority" to buy a Schedule 7 poison unless the substance is intended for non-domestic use (ie. for industrial, commercial or trade purposes). There is no cost to obtaining authority.

NORTHERN TERRITORY (NT)
Poisons Control, Department of Health, Northern Territory

t: 08 8922 7341
www.health.nt.gov.au

Manufacturers and wholesalers require a license and must comply with requirements of the license (which includes rules for storage, sale and record keeping). A retailer also requires a license with similar requirements.
A user requires a legal authority for which there is no fee, but for which there are requirements. For information about fees, authorisations and application forms, contact 08 8922 7341.

QUEENSLAND (QLD)
Drug and Poisons Policy and Regulation Unit, Environmental Health Branch, Public Health Queensland

t: 07 3328 9310
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.health.qld.gov.au

A Schedule 7 poison may only be sold by a person who has been licensed by the Chief Executive Officer to do so.
A licensee must ensure all Schedule 7 poisons are stored in a locked receptacle or storeroom, and keep personal possession of another responsible adult authorised by the licensee.
A licensee must make accurate records of all sales of Schedule 7 poisons. These records may be made in the form of an entry in poisons sales book, or by giving the purchase an invoice that has a unique number. The following details must be recorded:
  • Date of sale
  • Name and quantity or volume of the poison sold
  • Purpose for which the poison is required
  • Purchaser's name and address
  • If the purchaser buys the poison in person - the purchaser's signature
  • If the order was a telephone or written order - a note about the way the order was placed.

Usually a licensed wholesaler may not sell by retail. However, a licensed wholesaler may sell a Schedule 7 poison by retail to a person who uses the poison in a technical process connected with the person's business, industry or trade. The wholesaler must give the purchaser an invoice that has a unique number and states:

  • Date of sale
  • Purchaser's name and address
  • Name and quantity of the poison sold
  • All records must be kept for two (2) years

The application fee for license to sell a Schedule 7 poison is $265 and the renewal fee is $159. The application fee for a license to manufacture a Schedule 7 poison is $562.50, and the renewal fee is $456.50 a year.

SOUTH AUSTRALIA (SA)
Drugs and Poisons, Pharmaceutical Services and Strategy, Department of Health

t: 08 8226 7100
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.sahealth.sa.gov.au

Wholesalers of Schedule 7 poisons are required to be licensed. The license fee is $171 for 1 year. The license fee to manufacture a Schedule 7 is $255. Please note, fees change on 1 July annually. There are requirements for record-keeping associated with the license. Contact the SA Department of Health for further details and applications.

TASMANIA (TAS)
Pharmaceutical Services Branch, Department of Health and Human Resources, Tasmania

t: 03 6233 2064
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.dhhs.tas.gov.au/psbtas/

Licenses are required by sellers of a Schedule 7 poison and by all purchasers.

VICTORIA (VIC)
Drugs and Poisons Regulation, Department of Health, Victoria

t: 1300 364 545 or 03 9096 1067
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.health.vic.gov.au/dpu/

Manufacturers and wholesalers require a license to trade Schedule 7 poisons. A license to manufacture a Schedule 7 poison costs $695.30 for the first year and $245.60 for subsequent years. Manufacturing the product is defined to include all activities such as preparing for sale, repackaging, relabeling etc.

WESTERN AUSTRALIA (WA)
Pharmaceutical Service Branch, Disaster Management, Regulation and Planning Directorate, Department of Health, Western Australia

t: 08 9222 6883
e: This email address is being protected from spambots. You need JavaScript enabled to view it.
www.public.health.wa.gov.au

Licenses to sell permits to use are required for Schedule 7 poisons. Application for a wholesaler's license costs $600. To apply for a permit to use the product, the cost is $200.
In both cases, separate application forms are required for both the general application for a Schedule 7 poison and a specific hydrofluoric acid application.
In addition, depending on whether the application is for wholesale or use, various requirements must be met and experience must be demonstrated in those applications.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stainless Steel Threaded Fittings

For many years there has not been a Standard to cover the low-pressure stainless steel cast pipe fittings commonly used in Australia and other countries around the world.

These are are commonly termed "150lb" or "BSP" pipe fittings. In most cases the fittings that have been supplied were a mismatch of various Standards.

The fittings were dimensionally in accordance with a number of American Standards, whilst British Standard threads were used. This led to the fittings having threads that in some cases were non-compliant - basically there was insufficient length to accommodate the thread.

ASSDA, through its Technical Committee, identified this problem in the early 90s and through the publication of ASSDA's Technical Bulletin No. 1, highlighted the problems to the Australian market. ASSDA also looked for a mechanism to have these problems rectified.

Continue reading here


HF Acid Scheduling

Hydrofluoric acid is an aggressive substance used in the stainless steel industry, usually to assist in removal of scale and the chrome depleted layer associated with welds. This Technical Bulletin outlines changes to drugs and poisons schedules and state-by-state contacts on the subject.

Continue reading here or download PDF copy.


Airspace of Indoor Pools

Stainless steel is widely used in and around swimming pools and performs exceptionally well in most applications. However, some common types of stainless steel are not suitable for use in the airspace of indoor pool buildings in certain applications where they are subject to a tensile stress.

Continue reading here or download PDF copy.

For many years there has not been a Standard to cover the low-pressure stainless steel cast pipe fittings commonly used in Australia and other countries around the world.

These are commonly termed “150lb” or “BSP” pipe fittings. In most cases the fittings that have been supplied were a mismatch of various Standards.

The comparison of wall thickness of the DN 25 Half Socket , the new (left) and the old (right). The fittings were dimensionally in accordance with a number of American Standards, whilst British Standard threads were used. This led to the fittings having threads that in some cases were non-compliant - basically there was insufficient length to accommodate the thread.

ASSDA, through its Technical Committee, identified this problem in the early 90s and through the publication of ASSDA’s Technical Bulletin No 1, highlighted the problems to the Australian market. ASSDA also looked for a mechanism to have these problems rectified.

Typical DN 25 Hex Nipples - adopted thread length (as indicated by dimension marking) compared to the recommended length. ISO 4144 "Pipework - Stainless Steel Fittings Threaded in Accordance with ISO 7-1"

After investigating the alternatives it was decided that International Standard ISO 4144 could be the conduit to rectifying the problems. ISO 4144 in its 1979 form covered most of the committee’s concerns, but it did not allow for cast fittings - only wrought stainless steel.

After correspondence with the Australian and International Standard bodies, it was ascertained that ISO 4144 was due for revision, which presented a golden opportunity to have the standard rewritten to cover all of the Technical Committee’s concerns.

ASSDA was invited to represent Australia on the committee established to review the Standard and actively took part in the full process of its revision. Not all of the Committee’s recommendations were accepted. Finally, in early 2003 the new Standard was published.

What has been achieved?

The major improvements that have been adopted in the new Standard are:

a.    The use of castings as well as wrought materials.
b.    All cast fittings are to be properly heat-treated by solution annealing.
c.    The reduction in dimension, a more economical fitting.
d.    The thread standards allowed have been clearly defined.
e.    An introduction of pressure-temperature ratings for application of the fittings.
f.    The inclusion of eight new types of fittings into the Standard.
g.    The inclusion of DN 100 (4”) fittings.

Now that ISO 4144:2003 allows for the use of castings, Australia finally has a Standard that covers the products that have been in common use for many years.

The requirement that all castings are to be fully heat-treated will alleviate some of the corrosion problems that have been encountered in the past.

The dimensions of the fittings have been revised dramatically, thus giving a lighter and more economical fitting.

The wall thickness is the major dimension that has been reduced and it can be reduced by a further 20% if the fitting is made from wrought material.

ISO 7-1 sealing pipe threads are to be used on all fittings. The external and internal threads are to be tapered, but the internal threads may be parallel. The only exception to this is the threads on the Unions and their mating nut, which are allowed to have a variety of parallel threads.

Pressure temperature ratings for application of fittings have been specified (refer to Table 1).

Table 1 - Pressure-Temperature Rating

Some fitting types supplied into Australia were not covered in the old ISO 4144 Standard.

Eight new types have been included in the new Standard: these are 90° Reducing Female Elbows, Reducing Female Tees, 45° Equal Female Elbows, 90° Male x Female Elbows, Crosses, Reducing Nipples, Male x Female Unions and Male x Male Unions.

With the inclusion of the DN 100 (4”) fittings, the Standard now has a comprehensive range of products.

Some Disappointments with the New Standard

In the new Standard, apart from some minor editorial errors, there are two points of concern to the ASSDA Technical Committee.

Firstly, the new wall thicknesses that are stated as minimum could lead to a product being supplied that may not meet the expectations of the customer.

Even though the Standard allows for thin wall product, such thin walled fittings could be subject to distortion during the threading process or during installation. Care must be taken that this does not occur.

The second concern within the Standard is the length of the minimum external thread that has been adopted. The title of ISO 7-1 is “pipe threads where pressure tight joints are made on the threads”.

The minimum length specified can accommodate a thread that seals if it is manufactured to close tolerance. Care is required in manufacture to achieve this outcome.

Although it was recommended to the International Committee that it accept external thread lengths that could accommodate a thread at both ends of the tolerance range, the Committee did not adopt these recommendations.

Table 2 highlights the external thread lengths that were adopted compared to the external thread lengths that were recommended by Australia.

Table 2 - External Thread Length Comparisons
Conclusion

ASSDA believes minimum thread length is a concern to all suppliers and users of these fittings and care should be taken in their selection.

If mating fittings do not seal on the threads and interfere with the washout they may leak.

It is recommended that fittings should only be sourced from reputable and experienced manufacturers and supplied to ISO 4144:2003.

Overall, the Standard is a considerable improvement on what was available, and with care in the selection, the end user will be in a more certain and much safer environment than in the past.

Credits

This article was written by Kim Burton, Group Supply Manager of Prochem Pipeline Products Pty Ltd and an ASSDA Technical Committee member. ASSDA also acknowledges the contribution of Technical Committee member Peter Moore, Technical Services Manager of Atlas Specialty Metals, in the development of this article.


Download Technical Bulletin (April 1997)

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