In what state is the expansion joint delivered? Mistaken pre-tension and tie rod status, on-site installation will go wrong

Find out first: What exactly does the "delivery status" of the expansion joint mean?

It's not simply the four words "do a good job of packing" and it's done. The delivery status of the expansion joint is a complete set of technical definitions: whether the bellows is pre-deformed, where the tie rod nut is locked, whether the direction of the guide tube is correct, how to protect the flange sealing surface, and whether the transportation tool is assembled or disassembled. These details are bundled together, which determines whether you can hoist and weld directly after receiving the goods, or you have to squat on the site to do a bunch of pretreatments first.

Two days ago, I met a customer and received a batch of general-purpose corrugated expansion joints. I opened the wooden box and welded it. Halfway through the welding, it was found that the bellows was crushed to death, and the tie rod was still locked tightly-the manufacturer issued the transportation protection state, which should have loosened the nut and adjusted the pre-deformation before installation. And the result? As soon as the welding heat comes up, the bellows bulges directly. Who takes the blame? The delivery status was not clearly written in the contract, so the manufacturer sent it in the safest way, and no one understood it on the spot. The final construction period was delayed for one week.

What are the common delivery states?

Free Condition, Pre-Stretched/Pre-Compressed Condition, With Limit Tie Rod Condition, Overall Delivery and Part Delivery。

• Free state: The bellows has no artificially applied displacement and the length is equal to the design length. Most general-purpose corrugated expansion joints are sent by default, because they are safest and are not afraid of accidental collisions during transportation.
• Pre-stretched/pre-compressed state: According to the cold tightness of the pipe, the bellows is pre-elongated or compressed for a section, and then locked with tooling. It is commonly used in corrugated expansion joints in power station industry, or straight pipe pressure balance expansion joints that need to absorb large displacements.
• State with limit tie rod: The tie rod nut is locked to limit the bellows from shaking during transportation. But there is a pit here-some tie rods are for transportation protection, and they must be disassembled after installation; Some tie rods are working components, such as the tie rods of external pressure single axial expansion joint and double hinge transverse expansion joint, which are used to restrain axial force or distribute transverse displacement. If you dismantle them, you will have a big problem.
• Block Delivery vs Part Delivery: Small calibers are usually delivered as a whole; Large diameter thick wall expansion joints or non-metallic expansion joints may be shipped separately and reassembled on site. When the parts are delivered, flange bolts, gaskets and fabrics have to be counted separately, and one less is troublesome.

Why does the manufacturer send free state by default? Because the free state has the widest adaptability surface, the site can be adjusted according to the actual cold tightness value. However, some working conditions must be pre-deformed: for example, the design temperature of the pipeline is 500°C, the installation temperature is 20°C, and the thermal expansion is very large. If the bellows is not pre-stretched during delivery, the bellows may be pushed to the limit after operation, and the life will be greatly reduced.

How is pre-stretching and pre-compression achieved? Is the tie rod disassembled or not?

By tie rod nuts, or special tooling. The manufacturer uses a jack or screw to pull the bellows to the specified displacement before leaving the factory, and then locks it with a tie rod nut. On delivery, the tie rod has a lead seal or a yellow warning label that says "loosen nut before installation" or "strictly prohibited removal". But you must not just look at the label, you must look at the structure.

How to identify? Remember one thing:There are usually only one or two transportation protection rods, which are slender and directly connected to the flanges or connecting pipes at both ends, and the bellows cannot move at all after the nut is tightened; Working tie rods tend to be multiple uniformly distributed rods with spherical washers or spherical bearings that allow the bellows to generate lateral displacement.Take a practical example: the tie rod of the transverse expansion joint of a compound hinge. If you remove it, the hinge structure will lose its constraint, and the transverse displacement will twist the bellows. However, the short tie rod that comes with the general corrugated expansion joint from the factory, if it is not disassembled after installation, the expansion joint cannot be deformed at all, which is equal to a rigid short tube.

How to check the delivery status during acceptance?

• nameplate: Model, nominal diameter, pressure, displacement, factory number. Focus on whether there is a label "pre-stretch xx mm" or "cold tightness xx mm".
• Certificate of Conformity: Material, welding process, inspection date. Compare the contract to see whether the bellows material is 304 or 316L. Don't find the wrong delivery after a few days of rust.
• appearance: Whether there are bruises, scratches and pits in the bellows, whether the flange sealing surface is bumped, and whether the direction of the guide tube is consistent with the medium flow direction (the direction of the arrow must point to the medium flow direction). Flexible products such as non-metallic expansion joints and rubber compensators also depend on whether the fabric or rubber has wrinkles and cracks. They are easier to deform during transportation, so they must be laid flat or hung, and cannot be stacked.

Whether the tie rod nut is loose is also a key check item. If the nut is loose during transportation and the pre-deformation amount runs away, you have to measure the actual length of the bellows and compare it with the installation length marked on the nameplate. If the difference exceeds 5mm, don't hard install it, contact the manufacturer to readjust it.

Relationship between delivery status and installation status

Don't think that you can weld it directly when you receive the goods. Especially for corrugated expansion joints used in power station industry, pipelines often have strict cold tightness requirements. For example, the main steam pipeline has a designed cold tightness value of 30mm. When the manufacturer delivers the goods, it is pre-stretched by 20mm. When the ambient temperature changes during on-site installation, you may have to pull another 10mm. If there is no adjustment allowance reserved at the time of delivery, or the tie rod has been locked to the limit, then the scene is blind.

Look at the cold tightness table of the design drawing first, then measure the actual length of the arriving expansion joint, and then correct the cold tightness value according to the installation temperature. This process is called "secondary cold tightening". Some expansion joints have adjustment marks when they leave the factory, such as engraving lines on the tie rod to tell you how much displacement each turn of the nut corresponds, which is for the field micro-tuning.

Status of delivery clause written into the purchase contract

To avoid scrambling, these five articles must be clearly written in the contract:

• Delivery status: free state or pre-stretched/pre-compressed state, what is the amount of pre-deformation in mm.
• Nature of tie rod: whether it is a transportation protection tie rod (removed during installation) or a working tie rod (strictly forbidden to remove), and whether there is any mark.
• Shipping protection: with or without additional support, anti-collision wooden frame, bellows sheath.
• Packing Method: Wooden Case, Naked Package, Pallet. If the large-diameter thick-walled expansion joint is naked, the outside of the bellows must be wrapped with a protective pad, and the bolts on the flange surface should be coated with rust-proof oil.
• Storage period: Non-metallic expansion joints and rubber compensators are stored for more than 6 months, the rubber may age and must be turned over or deflated; If metal expansion joints are stored outdoors for more than one year, check the bellows for rust.

Don't bother, these terms would rather be written in detail than slapped on the head on the spot. And guess what? Many procurement disputes, finally check the contract, it says "delivery according to the manufacturer's standard"-what is the manufacturer's standard? Of course, people come by the most hassle-free.

Attached: Common delivery status comparison table

• Free stateApplicable to universal corrugated expansion joint and rotary compensator; Delivery length = design length; The site needs to be adjusted by itself.
• Pre-stretched state: Applicable to corrugated expansion joints and straight pipe pressure balance expansion joints for power station industry; Delivery Length> Design Length; Retest according to the requirements of cold tightness on site.
• Pre-compressed stateApplicable to working conditions with large axial compensation requirements; Delivery length
• With limit tie rod (transport protection): Suitable for long distance transportation; Must be loosened and removed before installation.
• With working tie rodApplicable to external pressure single axial type expansion joint and double hinge transverse type expansion joint; It is strictly prohibited to remove, but the nut can be adjusted to adjust the displacement distribution.
• Overall deliverySmall-diameter expansion joint, metal hose; Install as soon as it arrives.
• Parts deliveryLarge diameter non-metallic expansion joint, rectangular expansion joint; It needs to be assembled on site, and the parts list should be checked.

In what state the expansion joint is delivered, this question should not be remembered on the day of arrival. Before signing the contract, throw the real needs of your site to the manufacturer-free state or pre-stretch, how to deal with the tie rod, and the packaging is not in place. It is much more reliable to say it once than to call for help when you arrive at the scene.