C2572 02 Apr-May 06 AW - LP Gas Magazine

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ZINC SPRAYING ZINC – WHITE ELEPHANT OR WHITE KNIGHT? by Scott Ingram, quality manager, South Staffs Industries Ltd Corrosion protection on lpg cylinders has been a bone of contention within the industry for a number of years now, with more emphasis than ever placed on the importance of proactive measures to highlight the signs and prevention of corrosion. No wonder, when you consider that steel cylinders now equate to over 95% of the estimated 17 million cylinders in circulation (source: LPGA technical data 2004). We have all seen cylinders that have been returned from customers, in test, with the only failure being the deterioration of the paintwork – the topcoat cracked in areas that are rusting rapidly. From a cylinder integrity perspective, the cylinder may still be fit for purpose, but the excessive chipping of paint, although only an aesthetic problem, left unabated can, over a period of time, cause the cylinder to fail from corrosion. If you take into account the changes to the latest update of EN 1440 – Transportable Refillable Welded Steel Lpg Cylinders – Periodic Inspection, which states that, for a cylinder to receive a 15 year periodic inspection, the cylinder shall have “a system of external protection against corrosion that is being maintained”, this requirement falls under the responsibility of the REF EN 1439 TABLE 2 owner of the cylinder. WHAT IS CORROSION? How long do we have…? I could write a thesis on this (and many have!) and we would still be none the wiser. Fundamentally, corrosion is defined as “a state of deterioration in metals caused by oxidation or chemical action”. There are various types and causes of corrosion. One of the main types is electrochemical corrosion. This occurs when the metal comes into contact with an electrolyte – a fluid that conducts electricity, such as rainwater or salt spray – and the metal will gradually corrode away. This is the form of corrosion found on lpg cylinders. HOW DO WE CHECK FOR CORROSION? Defects Description Rejection limit Visual checks – cylinder corrosion is predominantly found on the base area of the cylinder or in the shroud area. These are areas that are prone to the trapping of water. This means that, at each fill, every cylinder has to be assessed against a set of criteria by the filling plant operators to establish if any corrosion is evident. Any cylinder showing signs of corrosion is segregated in accordance with the requirements of BS EN 1439 – Procedure for Checking Before, During and After Filling. This states that, prior to filling, the operator will segregate cylinders “which are faulty or defective, e.g. where there is damage to shrouds, carry handles, foot rings or dents, fire damage or corrosion”, and that “the foot ring shall be inspected for visible corrosion”. Types of corrosion, descriptions and rejection limits are listed below: Isolated corrosion pits A pitting of metal occurring in isolated areas When the depth of discrete pits exceed 0.6mm Excessive base corrosion. These requirements are somewhat difficult to adhere to if the cylinder still contains previous coatings. The most efficient way of working is to segregate any cylinder that has lost excessive coating, usually on the foot ring or shroud. These cylinders should then be sent for periodic inspection. Further inspections are then conducted to ascertain the full extent of the corrosion. If the cylinder is deemed fit for an additional 15- year cycle, the corrosion protection system should be reapplied. Any cylinder found with excessive corrosion above the requirements of the table should be scrapped immediately to prevent reuse. Area corrosion General corrosion Chain pitting/ line corrosion Crevice corrosion Reduction in wall thickness over an area not exceeding 20% of the cylinder surface A reduction in the wall thickness over an area exceeding 20% of the cylinder surface A series of pits or corroded cavities of limited width along the length or around the circumference Corrosion in the area of the intersection of the foot ring or shroud with the cylinder When the depth of any pit exceeds 0.4mm When the depth of any pit exceeds 0.2m When the total length of the corrosion exceed 50% of the cylinder circumference and the depth of any pit exceeds 0.4mm When the depth exceeds 0.4mm or if the depth cannot be measured HOW DO WE PROTECT AGAINST CORROSION? When cylinders are manufactured, AND at every periodic inspection interval, each cylinder SHOULD receive the application of a layer of corrosion protection. Corrosion protection is applied in an array of methods, including zinc phosphatebased primers; epoxy based coating; zinc powder; galvanising or metallic zinc spray. The pros and cons of each individual coating material and application method are fiercely debated, but the most common method used at present is metallic zinc spray. Although the metallic zinc 12 LP GAS MAGAZINE APRIL/MAY 2006
ZINC SPRAYING spray is perhaps not the cheapest option, it can demonstrate proven anti-corrosion properties over time. Each cylinder should be pretreated prior to any application. This basically means the cylinder body is cleaned so that its entire surface is free of any rust/ paint residue, etc, and that a suitable roughened surface is produced in order to accept the application. Shot blasting the entire external surface of the cylinder to the standard of SA 2 _ is most commonly used. After the previous coatings have been removed, we can get a clearer, more decisive view of the base metal. Particular attention should be given at this time to any cylinder crevices (the intersections of the foot ring or shroud with the cylinder). After shotblasting. Following the blast, the cylinders should have all surface areas coated with a layer of corrosion protection. It is of paramount importance to completely coat all corrosionsusceptible areas of the cylinder. Cylinders should be inspected to ensure consistency of coating. A minimum thickness of 40 microns is commonly used. However, some customers specify a thickness of 100 microns in corrosion prone areas. A final/top coat can then be applied, either by painting or powder coating. This seals the zinc coat and is used for cosmetic purposes. WHAT DOES THE CORROSION PROTECTION DO? It is widely known that some cylinders are handled poorly and often damaged due to a lack of operator knowledge. For instance, when a cylinder is being used to tar a roof and the cylinder is empty, the roofer often throws the cylinder off the roof, thus causing damage to the cylinder’s integrity, frequently dropping onto the shroud area or base ring. Often, the only damage found on a cylinder is the chipping of the top coating. Any paint chipping off the cylinder will result in water penetrating behind the coating. This has the potential to cause corrosion. Without corrosion protection, the steel shell of the cylinder is now susceptible to all adverse operating and weather conditions and will deteriorate quite rapidly. This deterioration will undoubtedly mean the cylinder will be returned with excessive corrosion prior to its 15- year periodic inspection being due. With corrosion protection, the zinc will act in a sacrificial manner and prevent the steel shell of the cylinder being exposed. Thus, the zinc coating and not the base metal will corrode over time, reducing the potential for the cylinder failing due to corrosion. This should ensure all protected cylinders will remain in the marketplace until their next 15 year periodic inspection. Zinc spraying. THE COST OF ZINC As mentioned previously, the cost of metallic zinc is high. At the time of writing, the cost of zinc wire has increased by 80% over the last twelve months. However, it should be noted that this still represents a good investment for protecting the longevity of the cylinder. WHAT SHOULD WE DO? n Ensure that all cylinders have corrosion protection applied at point of manufacture and at time of every periodic inspection, and that the thickness of this coat is specified – the usual thickness is a minimum of 40 microns. n Ensure all filling plant personnel are aware of the requirements for checking for corrosion, removing cylinders that do not reach the stated criteria and returning these cylinders for periodic inspection. This will hopefully ensure that both new and existing cylinders will be far less susceptible to corrosion and the life span of cylinders can be prolonged. Contact South Staffs Industries on 0121 522 2373 Integrated Gas Technologies Manufacturer of LPG low presusre regulators & LPG cylinder valve from Cemco South Staffs Industries Ltd LPG cylinder refurbishment and periodic inspection to EN1440:2005. All in accordance with our quality assurance system ISO 9001:2000. Compact Valves & Regulators – 20,21,22 mm Jumbo Valves & Regulators – 35 mm Snap-On Valves and Regulators – 27 mm POL Valves & Regulators Euro-outlet Valves and Regulators Tel: + 45 45 76 99 21 Fax: + 45 45 76 98 21 Email: sales@igt-lpg.com www.igt-lpg.com Zinc-sprayed cylinders for a longer life! For more details, please contact Chris or Steve on 0121 522 2373 sales@southstaffsindustries.com South Staffs Industries Ltd Bloomfield Rd, Tipton Dudley, West Midlands DY4 9EE LP GAS MAGAZINE APRIL/MAY 2006 13
Page 1 and 2: APRIL/MAY 2006 AUTOGAS CONVERSION E
Page 3 and 4: CONTENTS APRIL/MAY 2006 LP GAS THE
Page 5 and 6: If It’s autOGas EquIPmEnt It has
Page 7 and 8: What do you do for the LP gas indus
Page 9 and 10: Tankgas Equipment Ltd Specialist St
Page 11: DIRECTOR GENERAL launch of this at
Page 15 and 16: PRODUCTS Mitsubishi Launches Lpg Cu
Page 17 and 18: AUTOGAS CONVERSION EQUIPMENT NME Pa
Page 19 and 20: AUTOGAS CONVERSION EQUIPMENT Worldw
Page 22 and 23: AUTOGAS CONVERSION EQUIPMENT FROM H
Page 24 and 25: AUTOGAS Reaching Out to Europe Reco
Page 26 and 27: LPGA FOCUS SPRING MEETING REPORT Ov
Page 28 and 29: WORLD VIEW Nigeria Sets Regulatory
Page 30 and 31: TRAINING ABC OF ADR By Henry Laferl

C2572 02 Apr-May 06 AW - LP Gas Magazine

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