Key points
Process Plants are coming under more and more commercial pressure. Reduction in spend without affecting quality or performance is playing a major role in the day to day running of many sites. The implementation of a rupture disc stock rationalisation programme is proving to be a cost-effective way of improving efficiency while reducing long-term costs and future-proofing the plant.
Elfab Limited share its 80 years’ manufacturing experience and discuss the real benefits of rupture disc stock rationalisation to the modern process plant.
Reduce rupture disk stock holdings by 65% without increasing long-term cost
Leading rupture disc manufacturer, Elfab Limited, has over 80 years’ experience in the pressure management industry, supporting major industry players in maintaining a safe process environment across the globe.
Over this time, Elfab has developed industry-leading products to help implement a stock rationalisation program that has long-term sustainability and real benefits to the customer.
In this article, Elfab discusses the common issues experienced across a range of industries and explain how a rupture disc stock rationalisation program can help overcome such problems and improve process conditions – all while reducing overall spend.
The problem
Most industrial plants in the UK and Europe were built between 1960 and 1980 and were expected to operate for no more than 40 years. However, many are still operating today – several years past their expected life span.
Over time, process conditions within ageing plants can change dramatically. Even very small differences in process settings has resulted in plants holding an unnecessarily large variation of Rupture Discs onsite, or operating with product that was not specified or designed to operate under the current conditions.
As a result companies have found themselves holding an unnecessarily large amount of stock, or replacing rupture discs at a more rapid rate due to the design no longer being suitable for the way the plant is being operated.
Consequently, the risk of hazard and human error increases, as well as the complexity of stocking a large range of rupture discs with varying burst pressures and temperatures within disc specifications.
As process plants have been changing, rupture disc manufacturers have also been developing. Over the past 40 years, rupture disc technology has changed significantly. Manufactures have developed rupture disc solutions with superior technical features that if used correctly could irradiate many of the issues these aging plants are experiencing.
Elfab, shares its experience in working with major process plants and discusses some of the common findings that are leading to unnecessary overspending and high inventory levels.
Operating with out-of- date technology
Plants can be operational for a number of years without the need (or the chance) to introduce any new technology. They simply run on the technology that was available at the time of commissioning.
Over the past 40 years rupture disc manufacturers have significantly enhanced the performance characteristics of their rupture discs but companies have not always taken advantage of these developments.
Where once a single rupture disc specification was only suitable for a single location the development in tolerances and operating ratios may now allow companies to group similar product together.
Companies are commonly making purchases off datasheets written 40 years ago and not reviewing whether a more modern solution is now available, this can lead to a build-up of unnecessarily high stock levels, potential for obsolete stock, higher purchasing costs and inefficiencies in how the process operates.
Furthermore, in many instances operating conditions have changed significantly leading to a “creep” away from the intended functionality. Using a rupture disc that was designed for different process conditions can cause the product to fail early and incur higher and more frequent reordering levels or pose a danger to the plant, which should not go unaddressed.
Lack of global site data
Procurement systems have often been setup to identify each individual rupture disc as a separate item with its own part code and separate stock level, without recognising that one specification may be suitable for use in multiple locations.
Setting the system up in this way can lead to the purchase of additional stock when the system indicates that one of these parts requires replenishment, despite a suitable part being located elsewhere in the stock system.
Reliance on MRP Stock Levels
Relying on the data within a company’s MRP system can have a major impact on stock levels and unnecessary overspending as the system is only as good as the quality of information within it. In many cases, product is re-ordered without checking whether the product has been used.
In-house MRP systems automatically produce purchase orders when stock levels reach a pre-determined level. In some plants, a replacement unit is ordered as soon as one is used, this system does not allow the plant to benefit from economies of scale, as no discount is being offered by the supplier due to the low volumes being purchased.
Consequently, Stock controllers have been purchasing products to replace low stock levels without checking levels of demand or accuracy. Spare parts are being kept in stores that are no longer used or required, but simply because the company’s in-house system indicates that levels are low.
Lack of forward planning
Products are often purchased without long-term planning. A buyer may not be aware of future demand or potential requirement that the plant may have, and often only consider what is required at the time of ordering.
All rupture disc manufacturer’s offer quantity sensitive pricing, making it as cost effective to buy three rupture discs as it is to purchase a single unit. Rupture disc manufacturers recommended at least one spare rupture disc to be held in stores and a second is available as a backup during installation.
Too frequently only one disc is purchased which significantly increases costs and higher frequency of purchasing the same part.
Advantages of Rupture Disk Stock rationalisation Programmes
Today’s advanced rupture disc technology means that products have greater technical capabilities to suit a wider range of applications and installation points. Individual rupture discs can now offer a single disc solution for various process conditions which can eliminate up to 65% of previously problematic stock variation while significantly reducing long-term spend.
Rationalisation programs not only enhance stock management but overhaul the site with the latest rupture disc technology enabling significant processing efficiencies at the same time as cost reductions.
By investing in the latest technology, the plant will be able to run at maximum operating conditions without fatiguing the disc or affecting its life span.
Reduced stock variation
To introduce a successful stock rationalisation program and to allow customers to make significant stock reductions, advanced, reverse-acting, rupture disc technology must to be introduced across the process plant.
Traditional, forward-acting or graphite, rupture disc technology had limited technical characteristics, commonly manufactured with >10% tolerances and >80% operating ratios it was understandable why such stock variation was needed.
The characteristics of the latest reverse-acting rupture disc technology boasts advanced 3% tolerances with 97% operating ratios, the real driver behind the success of stock rationalisation.
By rationalising the plant through the capabilities of advanced rupture disc technology combined with greater flexibility across a wider material choice enables stock holdings to be greatly reduced, which in turn allows for significant cost savings.
One disc will be able to suit a larger amount of locations resulting in a much smaller stock catalogue. This enables multiple part types to be grouped together and replaced by one product part type that is technically capable for the combination of various process conditions.
A real reduction in stock value seen by customers who implement a stock rationalisation program in this way is typically 50-65%.
Purchasing Cost Reduction
Commonly rupture discs are purchased on a 3:1 ratio for each location (one disc and two spares). As all products supplied are quantity sensitive, large costs can be incurred when purchasing in such small numbers.
By undertaking a rationalisation scheme and replacing multiple outdated design with a 3% tolerance rupture disc, greater quantities of the same disc can be ordered to cover more locations around the plant, enabling procurement to benefit from lower purchase prices through economies of scale.
Furthermore, rather than hold two spare discs for every location, a small number of spare discs can be held in stores that will suit multiple locations therefore reducing the stock holding even further.
Future proofing
By implementing a rationalisation programme, all discs will be manufactured using the latest reverse-acting rupture disc technology, which boast tighter tolerances and operating ratios, smooth surface finishes and increased vacuum and cyclic resistance.
As well as a reduction in stock such advancements in performance characteristics can significantly improve the lifespan of the product, reducing long-term costs through a reduction in spares orders. With the most technically superior rupture disc designs being tested to over one million life cycles, reverse acting technology has significant benefits over traditional forward acting technology.
Reducing the risk of Human Error
By rationalising the plant and reducing the variation, the number of transactions subject to potential error will decrease. A reduced number of different disc specifications simplifies purchasing processes and leads to fewer mistakes being made.
This simplification is also of benefit to plant maintenance technicians and reduces the need for training, as staff will only need to know how to install one type of rupture disc. Overall, costs are reduced and installation quality improves.
How to implement a successful rupture disk rationalisation programme
In order to implement a rationalisation programme successfully, there are certain aspects which need’ to be addressed internally to the plant to benefit from the advantages that a rationalisation scheme has to offer.
Key areas for consideration are:
Material Standardisation
Rupture disc material selection has traditionally been dependent on the individual process conditions of each unique application. By standardising on material choice and opting for a material that suits every installation point, this will allow for combined purchasing going forward.
By implementing this strategy, it will simplify the reordering approach as all tag locations will have a standard material specified compatible with the individual process conditions. Research has shown that Hastelloy rupture discs offer superior stability across temperature ranges, with a drift < 5% vs graphite >35% for temperatures of up to 200˚C.
Reconfiguration of Process Conditions
Rupture disc rationalisation can have a significant impact if process conditions are streamlined across the plant. Most process plants require no more than a +/-5% tolerance for the rupture discs, reviewing conditions in line with rupture discs offering 3% tolerances can reduce the number of different disc types that are required to cover the site. If similar processes can be brought in line with one another, then two or more different tag locations can be addressed with one pressure relief solution.
Change of Buying Habits
Rather than purchasing only what is required at the time, future demand forecasts should be taken into consideration to benefit from discounts for higher quantities. This will allow the purchaser to acquire the discs at a reduced unit price and save costs going forward.
Introduction of a Contractor Procedure
Contractors on site have traditionally bought what they deem to be the best product for their specification and budget, without contacting the plant owners. This has resulted in a lack of consistency through the plant, with discs from different manufacturers being installed.
By creating a standard procedure and catalogue for contractors, they will only procure items from the plant owner’s preferred supplier. New sections of the plant will be designed in accordance with the standard conditions already in place on the plant.
Conduct a site survey with the rupture disc manufacturer
Conducting a site survey it’s the most effective way to ensure all tag locations are identified and the most realistic cost savings can be offered. Such a survey will ensure that any issues with future obsolescence is irradiated, future proofing the site.
Manufacturers can undertake the survey with a representative of the plant to ensure the correct data is gathered and analysed prior to rationalisation. This will eliminate any errors in the rupture disc register that might have occurred since the plant has been running.
By looking over the data and combining tag locations with similar burst pressures and sizes, reduced list of rupture discs can be compiled. Manufacturers can then propose a site wide solution.
