No - a full UBI should replace all of those programs.
Welfare yes.
Social security and government pensions? No.
Those two are retirement programs which are paid for by contributions of a percentage of salary by both the employee and the employer. (In the case of government pensions, the employer is the government entity they work for. Upon retirement, the retiree gets a benefit based on their contributions and wage history. UBI would not replace that.
As an example: Suppose UBI is $2000/month. Your wages are $4000/month, but you contribute 8% to your pension plan (social security is 6%), it really comes out to $3680 (Ignoring taxes and other deductions. Your living income then is $5680/month.
If UBI eliminates your pension (or social security), it will be very difficult to retire as your income will drop from $5680/mo to $2000/mo. Could you live on that? Probably. But your standard of living post retirement would drop drastically.
Unless UBI increases after retirement, it doesn't replace retirement benefits.