Installation of Pig Closures

Initial  Installation

The initial installation of the Pig Closures should strictly abide by these rules:

The pig closures and equipment, their inside diameter should be consistent, clearance should be average, the clearance tolerance between the maximum and minimum ≤1.0 mm, and the unfitness of the butt joint should meet the standard of GB150.4-2011 Form 1. When the wall thickness of the connection conforms, it will take the thinner one to calculate.

Before the closure of the equipment barrel, the welding form must be confirmed:
1) If taking two-side welding, it needs to remove the head cover (2.1 Headcover dismount);
2) If taking one-side welding, it needs to remove the seal only.

Welding and welding distortion control

It can distort due to fabrication, welding, and subsequent post-weld heat treatment (PWHT), which is minimized.
The following recommendations should be followed to minimize this risk:
Make sure the unfitness gap is coincidental, and tolerance should be ≤1.0mm between the maximum and minimum.
The unfitness of butt weld should meet GB 150.4 Form 1. If the wall thickness conforms, take the thinner one to calculate.
The welding sequence of symmetrical welding must be adopted, which is very important for controlling welding deformation.
Using the small electrode and low-current multilayer welding to control the welding distortion can cause the head cover to be unable to open or close. Very important.
The welding parts on the equipment should be as far away as possible from the girth weld between the quick-opening blind plate and the equipment cylinder. 

PWHT recommendation

Take the local heat treatment (take the heat treatment special heating track)

If it must take the bulk heat treatment, it should use rock wool, aluminum silicate, or other heat preservation to protect the seal face.

The technology for heat treatment should be carried out generally by ASME VIII or GB150.4 8.2.

Before PWHT, remove all the seals. After PWHT, lightly emery cloth (smooth finish paper) the closure hub sealing face and smear the grease, glycerine, or anti-corrosive grease.

Painting

Before painting, you should prepare for the below tasks:

Twine both sides of the hand wheel and screw with plastic cloth.

Keep out the oil hole and welding groove.

Remove the safety pin, safety screw, and connection plate, and position the hand wheel.

It is essential to do the above preparation before painting! It can avoid affecting the assembly’s accuracy and performance, prevent sandblasting and paint from entering, and make the product’s appearance beautiful

Headcover restoration

Operation of Pig Closures

Before attempting to open the closure, check that the vessel isolating procedures have been fully adhered to and drained.

Rotate the button of the safety interlock device and turn it on. Then, if there is still pressure, we must stop it right now. Recheck the atmospheric valve and blow down valve. Wait until the equipment is completely drained.

Rotate the button of the safety interlock device and turn it on. Then, if there is still pressure, must stop it right now. Recheck the atmospheric valve and blow-down valve. Wait until the equipment is completely drained.

Maintenance of Pig Closures

Maintenance activity

If there are some problems with opening or closing:
1) remove the protection mask and lubricate all the turning points;
2) Check whether the components are deformed or not; 3) During the procedure, pay attention to the screws, which must be fastened without being loose.

When storing it, avoiding the sealing surface and the fitting surface is important, it can prevent the seal elements from damaging and aging and increase the service life.

Seal replacement

Should it be necessary to remove the door seal from the closure, this can be achieved simply by picking the seal out of the groove with a flat-bladed tool under the seal lip, making sure the seal and the seal groove are not damaged.

With the seal removed, the seal groove should be wiped clean of all loose impediments and corrosion deposits. A thin layer of Silicon-based grease should be applied to the seal groove before replacing the seal.

To fit the seal, first press the seal at 12 o’clock and 6 o’clock; the seal should then be fitted at 3 o’clock and 9 o’clock. Don’t put back the seal, and the U-type seal should be facing outside.

Hint: Lubrication of the seal groove will assist in this operation and general seal replacement to prevent corrosion.