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Inspecting the Overhead Travelling Crane
This article is the second in a series on overhead cranes. In part one, I discussed the details of overhead crane inspection. This week I will provide a quick review of the inspection and testing requirements for overhead traveling cranes. This includes gantry cranes that are commonly found in shops across Alberta and Canada.
Overhead cranes fall under OH&S “Part 6: Cranes, hoists and lifting devices” and you can find a Work Safe explanation of the code here: http://work.alberta.ca/documents/WHS-LEG_ohsc_p06.pdf. OH&S directs everyone to CSA C22.1 and C22.2 for electrical components. It also references CSA B167-96 for design, maintenance and inspection. In this article, I will focus primarily on the items covered in CSA B167-96 since this covers much of the work Sparta is involved in.
If you think you need an inspection, don’t hesitate to contact us and schedule an inspection.
The design of overhead cranes can be a fairly complex endeavor and describing it fully would require a lot of detail and explanation. However, there are few key points that get decided during the design phase that have impact on the end user and are worth being aware of.
The first point worth noting is the classification of crane. The class of the crane is determined based on the operating conditions and duty load and ranges from A1-A8. Aside from the impact this has on engineering (specifically when selecting grades of steel and designing for fatigue), this classification of the crane also dictates the intervals of inspection and maintenance. The majority of the overhead cranes in most industries will be classified as regular to light duty and be grouped in A1-A3 classes. Some noticeable exceptions are foundry cranes and scrap yard cranes that use magnets. If this information isn’t provided by the original manufacturer, a qualified person can help define it.
Most companies won’t get involved in fabricating overhead cranes but if the opportunity arises the fabrication (in Canada) needs to be done according to CSA W59 in a CWB shop. That is to say that you need qualified personal follow a qualified procedure constructing the crane. W59 also lists the post fabrication inspection requirements. It is also helpful to have some form of quality program such as ISO: 9001 in place to maintain a high quality product.
After the crane has been designed, built, and installed, the next section to worry about is testing and commissioning. To commission a crane, you will need verification that a professional engineer has reviewed the design and installation of the supporting structure, and that there is a stamped certification to accompany the crane. Testing is to be done in accordance of ISO 4310 and is meant to test functionality of the crane.
Testing will include:
(a) all motions;
(b) limit switches at full speed;
(c) limiting and indicating devices;
(d) all circuits, controls, interlocks and sequence of operation;
(e) each crane motion, holding brakes and travel brakes with the hook carrying
-rated capacity – during these tests the specified speeds are to be attained, provided the power supply to the crane is as specified, and
-125 percent of the rated capacity – during this test the specified speed need not be attained but the crane must show itself capable of dealing with the load without difficulty.
It is also required that the maximum deflection while under load is verified to match that of the design data that comes from the steel construction handbook. It is required to be L/600 or L/300.
After proper testing and verification the crane is now ready for regular service. Ongoing maintenance and inspection are now required to follow the intervals laid out in B167.
The inspection requirements are split into operational inspections and periodic inspections. Operational inspections occur at the beginning of each shift from ground level by an internally qualified person.
Work Safe Alberta says (http://work.alberta.ca/documents/WHS-LEG_ohsc_p06.pdf) the following which is adapted right from the CSA code:
The operational inspection must include, but not be limited to, the following:
(a) all operational functions;
(b) leakage in line, tanks, valves, pumps and air or hydraulic systems;
(c) deformed, worn or cracked hooks;
(d) hook latches;
(e) hoist ropes;
(f) limit device(s) for function; Occupational Health and Safety Code 2009 Part 6 Explanation Guide 6-50
(g) function labels for operator control;
(h) all brakes.
Any defects found in this inspection must be corrected by a qualified person. Periodic inspections occur on intervals based on the service class but the majority of cranes will require annual inspections. Periodic inspections are required to be done by someone with a substantial amount of crane experience (usually third party) and it is a much more thorough look at the crane’s safety. Inspectors will require a minimum of 10,000 hours of experience related to the overhead crane industry or be directly supervised by a professional engineer in order to perform the inspection. Periodic inspections differ from operational inspections in that they also require an inspector to do the inspection from elevated position rather than just from the ground.
A periodic inspection includes everything the operating inspection requires in addition to looking for structural problems, wear, deformation and cracks among other things. Both operational and periodic inspections are required to be documented and stored in the log book.
Anytime a crane sees an unexpected loading scenario that is outside of its defined parameters we call this a misadventure. For overhead cranes, a misadventure could be an overload from too much weight on the hook, a high dynamic load applied from the crane in a number of ways including load shifting, collision on the hook or many other things. B167 doesn’t specifically have a section for misadventures but does have all the information spread over a few different sections. The code suggest that if your crane is subjected to any of these loading scenarios that you immediately put the crane out of service, perform a periodic inspection, and consult with an engineer.
Occasionally, the need arises to overload a crane in a planned way. In my experience this usually happens for installation or during a special project outside the normal scope of business. If this is the case, it is recommended that you consult and engineer before exceeding the rated capacity of any crane.